FETAL GROWTH AND DEVELOPMENT

OF THE PIG

by

REBECCA LEANN McPHERSON-McCASSIDY, B.S.

A THESIS

IN

ANIMAL SCIENCE

Submitted to the Graduate Faculty of Texas Tech University in

Partial Fulfillment of the Requirements for

the Degree of

MASTER OF SCIENCE

Approved

Chairperson of the Committee

Accepted

Dean of the Graduate School

December, 2003

-•\KNOWLEDGE\ENTS

I would like to thank the members of my graduate committee: Drs. Michael

Galyean. .Tohn McGlone, and Guoyao AVu for their time and contributions to this thesis.

Their guidance and professionalism were greatly appreciated.

I would like to especially thank my advisor, Dr. Sung Woo Kim for the patience

and courtesy shown to me tluoughout my project. It was an honor to work under such an

outstanding scientist w-ho never accepted second best. You opened many new doors to

science I thought never possible and set an example on how to be a knowledgeable,

professional member ofthe scientific community.

I am extremely grateful to the many other individuals who helped considerably

with this project. I would hke to tharijk Edv.'-ard Carrasco, Stanley Harris, and Jerry Smith

for all the help and support they provided at the farm, I would like especially to thank

Sheila Finlay for her help in the collection part of this project. I am also very grateful to

Jeff Dailey for all the computer help he provided me. I want to thank Clay Dehn,

Rachelle Hardage, Lindey Hulbert, Ann McDonald, Anthony Rudine, and Barbara Smith

and for all their additional help, including listening to my many presentations, thank you

for your friendhip and support. Lastly, a special thanlcs goes to Fei Ji for all his help,

advise, and support, it was a pleasure working with you.

This thesis is dedicated to my mother Karen Mcpherson and my imcle Robert

Litter, thank you for all your suppoit.

TABLE OF CONTENTS

ACKNOWLEDGEMENTS ii

LIST OF TABLES v

LIST OF FIGURLS vi

CHAPTER

I GENERAL INTRODUCTION 1

Literature cited 3

IL LITEIL^TURE REVIEW 4

Current knowledge of fetal growth and development In the pig 5

Maternal factors associated with fetal pig development 6

The Uterine environment 10

The placenta ^^

Scope of this thesis 1 -

Literature cited 14

III. FETAL GROWTH IN THE PIG: NUTRITIONAL IMPLICATIONS 17

Abstract 17

Introduction 1"

Materials and methods -0

Results

Discussion 29

Implications 32

Literature cited 46

IV LITTER CHAR.\CTERISTICS AND INTR.\UTERINE LOCATION IN RELATION TO FET.'VL GROWTH .AND DEVELOPMENT IN THE PIG 48

x'Vbstract 48

Introduction 50

Materials and methods 51

Results 53

Discussion 55

Implications 57

Literature cited 71

LIST OF TABLES

Table 3.1 Composition of gestation diet. j j

Table 3.1 The number of gilts used per day of gestation and the number of fetuses collected 34

Table 3.3 Chemical composition, on a percent dry matter basis, ofthe fetal carcass during different days of gestation 35

Table 3.4 Chemical composition, on a percent dry matter basis, ofthe fetal brain during different days of gestation 36

Table 3.5 Chemical composition, on a percent dry matter basis, ofthe fetal GIT during different days of gestation 37

Table 3.6 Chemical composition, on a percent dry matter basis, ofthe fetal heart during different days of gestation 38

Table 3.7 Chemical composition, on a percent dry matter basis, ofthe fetal liver during different days of gestation 39

Table 3.8 Chemical composition, on a percent dry matter basis, ofthe fetal lung during different days of gestation 40

Table 3.9 Chemical composition, on a percent dry matter basis, ofthe fetal placenta during different days of gestation 41

Table 3.10 Chemical composition, on a percent dry matter basis, ofthe

fetal kidneys during diiTerent days of gestation 42

Table 3.11 Weights of fetal tissues (g) on different days of gestation 43

Table 4,1 Litter weiaht variation within dav of gestation 58

LIST OF FIGURES

Figure 3.1 The fetal GIT to fetal weight ratio {%) increased as day of gestation progressed. The fetal liver to fetal weight ratio {%) decreased as day of gestation progressed 44

Figure 3,2 Wliole fetal v/eight increased as day of gestation progressed 45

Figure 4.1 The weights ofthe whole fetus (g) decreased as location proceeded cranial to cervical, when data v/ere pooled in the analysis 59

Figure 4,2 Weights ofthe whole fetus on d 60 of gestation decreased as fetal location proceeded cranial to cervical, when day of gestation was not considered 60

Figure 4.3 Fetal Uver weights (g) by different uterine location on d 45 of gestation 61

Figure 4.4 Fetal GIT v/eights (g) by different location on d 60 of gestation 62

Figure 4.5 Fetal liver weights (g) by different uterine location on d 60 of gestation 63

Figure 4.6 Fetal heart weights (g) by different uterine location on d 60 of gestation 64

Figure 4.7 Fetal lung weights (g) by different uterine location on d 60 of gestation 65

Figure 4.8 Fetal kidney weights (g) by different uterine location on d 60 off gestation 66

Figure 4.9 Fetal liver weights (g) by different uterine location on d 75 of gestation 67

Figure 4.10 Fetal liver weights (g) by different uterine location on d 102 of testation 68

Figure 4.11 Fetal heart weights (g) by different uterine location on d 102 of gestation 69

Figure 4.12 Fetal heart weights (g) by different uterine location on d 110 of testation 70

CHAPTER I

GENERAL INTRODUCTION

In the nineteenth century, Louis Pasteur performed an experiment observing that

flies did not come from rotting meat; rather flies came from other flies that laid eggs on

the meat. With this, he successfully demonstrated to the world that life could only come

from life (Dubos, 1986). This simple observation created a revolution that changed the

way science was viewed. This finding initiated farther studies and enhanced human

curiosity as to how life forms. Now in the twenty-first century, many questions still

remain unanswered conceming how the seemingly complex and intricate process of fetal

growth and development occurs.

Because fhe events that occur during the fetal development process ultimately

influence fiiture growth and development after birth (Allyson et al., 2001), the study of

fetal growth and development is of crucial importance. Gaining answers to three

questions how, when, and why certain developmental events take place, will lead to a

better understanding ofthe fetal development process as a whole. Developing the

answers to properly address these questions, will lead to new innovations in the

explanation and understanding of what is needed to reach optimum fetal and postnatal

growth for both humans and animals.

The purpose of this study was to investigate fetal growth and development in the

pig. With the human population on the rise, it is a pressing concem in the field of animal

production to increase animal output. Because the pig is a litter-bearing animal, with a

high ovulation rate, short gestational cycle, and early age to maturity, it serves as an ideal

food animal. A better understanding of fetal growth and development in the pig, will lead

to better management strategies to reach optimum growth. Therefore, the objective of

this thesis was to characterize fetal growth and development in the pig by: 1) identifying

when major organ development occurs during the gestation period (Chapter III), and 2)

characterizing fetal growth and development as well as fetal weight changes related to

intrauterine location ofthe individual fetuses (Chapter IV).

Literature Cited

Allyson, K. C., N. Stickland, and C. Stickland. (2001). Porcine satellite cells from large and small siblings respond differently to in vitro conditions. Basic Applied Myology, 11:45-49.

Dubos, R . J. (1986). Louis Pasteur, Free Lance of Science (pp. 1-30), DeCapo Press, Cambridge, MA.

CHAPTER II

LITERATURE REVIEW

The domestic pig of today originated from the Eurasian wild boar (Sus scrofa)

(Guiffra et al., 1999). Since their first domestication pigs have had an increasing effect

on economic and social importance in animal agriculture. With over 180 types of pig

found on every continent except Antarctica, and over 377 known breeds, the domestic pig

has many important uses. In today's market the pig is widely used to supply a variety of

meats, leather, and medical products.

The pig also plays a historical role in the United States; one example is the well-

known story that during the war of 1812, a New York pork packer named Uncle Sam

Wilson shipped several barrels of packed pork to U.S. troops. The barrels were each

stamped U.S across the top, thus Uncle Sam was quickly coined.

The importance ofthe pig is evident, not only in its historical role, but as a highly

demanded commodity as well. World pork trade continues to increase as the demand for

pork and pork products increases. In 1999, the United States alone exported a reported

554,000 metric tons of pork valued at $1.2 billion dollars. The Intemational Food Policy

Research Institute predicted that overall world pork consumption will increase by 165

percent from the 74 million metric tons produced in 1993 to an anticipated 122 million

metric tons by 2020 (Pork Board, 2000).

It is clear that pork production has an increasing importance in today's market

place. Ultimately, the total number of live pigs produced each year determines the

profitability of the producer. When determining the number of pigs produced per sow

per year, with the growing need to produce more piglets, it is important to first

understand how the piglet develops in the uterine environment. With an increased

understanding of fetal grow1:h and development, there would be a better understanding of

what is required for optimum intrauterine and postnatal growth. This literature review

covers the current knowledge of fetal pig development and addresses factors that directiy

and indirectly influence fetal growth and development in the pig.

Current knowledge of fetal growth and development in the pig

Though the study of fetal growth and development is not new, much remains

unanswered how this intricate process works. In 1965, Ullrey et al. (1965) used 179

unbom fetuses from various stages ofthe gestation cycle, and 35 newly bom piglets from

19 Yorkshire gilts to study fetal growth and development in attempts to characterize a

"normal" standard for organ weight during gestation. These findings opened the door to

a new wave of developmental research to answer specific questions as to when certain

organ and tissue development occurs. Knight et al. (1977) did fiirther work in

characterizing the placenta and indicated that placental development occurs between d 20

and 30 of gestation.

More recently, Silva et al. (2000) performed a similar study to further investigate

fetal pig development during gestation. This study observed the correlation between fetal

size and total fetal organ weight throughout gestation. It was indicated that the liver,

lungs and kidneys on d 30, 45, and 60 were most affected by day of gestation, and by

total fetal weight. It was further observed that on d 100 of gestation, fetal size did not

influence fetal organ weight. Chemical analysis indicated to the authors that as day of

gestation progressed, the level of DNA, RNA and protein increased in all tissues, but they

were not directly affected by total fetal size. A weak correlation was observed between

fetal weights and uterine location, with those fetuses found at the cervical end having the

greatest tendency to be smaller. These data show that fetal development does not occur

at a uniform rate, and that organ development occurs at different days of gestation.

Rather, the fetal development process is dependent on day of gestation.

With answers beginning to emerge as to when developmental processes occur,

other questions begin to arise to try to answer what factors influence the fetal growth and

development process.

Maternal factors associated with fetal pig development

There are numerous factors that directly or indirectiy influence the fetal

development process. One ofthe most important determinants as to how successfully a

fetiis will develop lies in the hand ofthe matemal factors. Factors such as maternal

genetics, matemal health, and maternal nutrient intake heavily influence and control the

process of fetal growth and development.

Matemal genetics

Genetics has come a long way in improving breed and desired characteristics.

Today there are several variations of genetic selections from which to base breeding

decisions on. Genetic make-up influences several desirable production traits, such as

meat quality, reproductive performance and litter size. Because consumers continually

demand higher quality pork products, the frend for the past 30 yr has been to focus

primarily on growth rate and carcass learmess improvement (Gibson et al., 1998).

It is important to select for those traits that will improve overall performance

values at the neonatal and postnatal development period. However, selection for some

traits, such as reproductive performance, is difficult due to low heritably (Moeller et al ,

2000). Breed characteristics also heavily influences genetic traits. A recent study by

Damgaard et al. (2003) demonstrated when comparing the Landrace and Hampshire

breeds, Hampshire's had lower genetic variance for back fat. Some genetic traits have

been found to compliment other highly desired fraits. Chen et al. (2002) demonsfrated

that selection criteria for leanness also improves growth rate; however, there are those

genetic traits that have negative correlations with other desired traits. Such an example

was implied by Moeller et al. (2000), with a hypothesis that the lack of improved

breeding values for the Hampshire breed might be due to the negative correlation found

between reproductive and carcass traits.

It is a challenging and daunting task to select for those desired industry fraits,

such as increased litter size with a decreased mortality and improved meat quality. When

selecting for an improvement of total litter size and postnatal growth, a higher demand is

placed on the matemal ability to adequately care for the litter, both during the neonatal

and postnatal period (Grandinson, 2003).

Matemal health

The overall health ofthe sow can be defined in several forms. The sow's outer

physical state may hinder her ability to cope with the surroundings. There are several

lameness issues, all of which can adversely affect the sow's ability to produce, either by

compromising her ability to receive enough feed, by influencing her ability to

successfully complete the reproductive cycle, or by decreasing her overall state of

welfare. Shoulder sores, ulcerated granulomas, osteochondritis dessicans, and overgrown

feet are just a handful ofthe lameness found in current sow herd (Merck, 1998). Sow age

and body mass play an important role in the sow's health status before and after the

gestation cycle. Giesemann et al. (1998) observed that when mature sows were

compared to younger sows, sows that were more mature in age had larger, more

mineralized, and thus stronger bones. Mature sows were also found to consume more

feed during lactation and therefore consumed and retained more Ca and P. The amount

8

of feed consumed during the lactation period is critical to the developing postnatal

piglets, as it determines how well the mother will produce colostmm and milk.

Sow body mass can further impact reproductive performance, which will

ultimately be the deciding factor as to how well a fetus will develop, if at all. It has been

reported by Clowes et al. (2003) that sows that had an increased body mass, and lose the

least amount of protein during lactation, had an increased ovarian function and a higher

litter performance at weaning.

The environment that the sow is housed in before and during gestation can

dfrectly influence overall health and thus impact her ability to successfully produce a

viable litter. Heat sfress can cause exfreme distress in a gestating sow. It was observed

in an Iowa State University study that sows not provided with an adequate drip cooling

mechanism suffered from excessively high respiration rates (Honeyman et al., 1999)

which hindered normal physiological function and production. Thermal stress can cause

an otherwise healthy sow to abort, have an increased occurrence of stillbirths, have

reduced ovulation rate, and have reduced milk production (Merck, 1998). The sow's

overall welfare and health state should be taken into serious consideration if optimum

neonatal and postnatal growth is to be achieved at a maximum rate.

Matemal nutrition

The sow's nutrition affects fetal groMfth, as the sow serves as a type of nutrient

reservoir for her developing fetuses; however, it is not currently known whether this

matemal reservoir can properly or adequately supply all ofthe developing fetuses equally

throughout gestation (Mahan and Vallet, 1997). Sow's nutrient requirements for certain

vitamins and minerals can fluctuate during gestation (Mahan Vallet, 1997). Currentiy the

majority of gestating sows are fed one diet once a day for the entire gestational period,

approximately 114 d. The gestation diet is based on maintenance requirements, target

weight gain, and conceptus outcome. It is an increasingly challenging task for swine

nutritionist to devise a proper feeding strategy for the gestating sow. Recent data suggest

that fetal growth increases exponentially during d 50 through 110 of gestation. This

indicates that during early gestation the sow is overfed but underfed during late gestation

(NRC, 1998). It has been observed that sows undernourished for the first few days ofthe

estrous cycle have approximately a 15% decreased rate of fetal survival (Almedia et al.,

1999). Because all phases ofthe reproductive cycle directly influence each other,

nutritionists are faced with devising a plan that allows the sow to successfully support

maximum fetal growth, yet at the same time does not hinder her feed intake during

lactation and thus still allow her to have maximal mammary gland growth (Kim et al.,

1999).

The uterine environment

Though simple looking in appearance, with two homs supplied by a single

branching artery, the utems is acttially quit complex. The utems will house the

developing fetuses in a protective and ideal environment for growth to occur. The

10

uterine fimction influences the growth rate, development, and survivability ofthe fetuses,

by regulating growth factors and needed nutrients. The utems is also responsible for the

production of many growth factors as well as the incorporation of certain nutrients

(Vallet et al., 2002).

Uterine blood flow

The sow is a litter bearing animal that has two uterine homs. Both uterine homs

supply the growing fetuses with a single uterine artery that branches at the base ofthe

homs. The blood supply then travels up the hom to the cranial most extremity where it

begins the process of delivering nufrients to the individual fetuses, via the placental

artery, fraveling down the hom until it reaches the last conceptus at the cervical end

(Merck, 2000). It has been indicated that the concentration of carbon dioxide found in

the arterial blood is an important determining factor on regulating blood flow throughout

the utems ofthe pregnant sow (Hanka et al., 1975).

The placenta

Because the matemal-fetal nutrient link is not direct (Fall et al., 2003), the

placenta serves to support fetal growth by transporting respiratory gases, nutrients, and

wastes between fettis and mother (Reynold and Redmer, 1995). The amount of maternal

nutrients supplied to the growing fetuses determines how well those fetuses will develop

(Bauer et al., 1998). Fetal under-nutrition causes fetuses to develop inadequately and

II

often lead to lighter birth weights (Fall et al., 2003). The placenta serves to not only as a

supply line for matemal nutrients, but it also produces many hormones and their

corresponding receptors (Bauer et a l , 1998). How efficient the placenta is at producing

hormones and fransporting nufrients will also determine how well fetal grov^h occurs.

Placental efficiency can be seen as a characteristic within the Meishan pig. It is known

that this breed has a decreased placental size with an increased piglet weight. This

knowledge suggests that selection based on placental size and efficiency can be used to

optimize piglet weight (Wilson et al., 1999).

Scope of this thesis

The ongoing study of fetal growth and development is important if optimum

neonatal and postnatal development is to be achieved. Gaining a better understanding of

fetal growth and development events that take place within the safe surroundings ofthe

uterine environment will lead to a better understanding of what is needed to reach a more

optimum neonatal and postnatal growth. It is known that there are large weight

variations among siblings within a given litter. Why there is such a variation is one of

many questions yet to be answered. It is further unknown whether the sow receives

enough nutrition during the entire gestation cycle to adequately supply her growing litter

during gestation and after birth, while allowing enough nutrition to adequately support

vital matemal nutrient need. Much still needs to be determined about the fetal growth

and development cycle. Therefore, the purposes of this thesis were to obtain a better

12

imderstanding of fetal growth and development during gestation by 1) identifying when

major organ development occurs (Chapter III); and 2) characterizing fetal growth and

development, as well as weight variations related to intrauterine location ofthe individual

fetuses (Chapter IV). This information will allow for the better understanding of how,

when and why certain important developmental events take place.

13

Literature Cited

Allyson, K. C , N. Stickland, and C. Stickland. (2001). Porcine satellite cells from large and small siblings respond differently to in vitro conditions. Journal of Basic Applied. Myology, I I , 45-49.

Almeida, F., and G. Foxcroft. (1999). Physiological mechanisms mediating embryonic survival in pigs. Advances in Pork Production, Alberta Pork Research Centre. 10 (Absfr.).

Bauer, M. K., J. E. Harding, N. S. Bassett, B. H. Breier, M. H. Oliver, B. H. Gallaher, P. C. Evans, S. M. Woodall, and P. D. Gluckman. (1998). Fetal growth and placental function. Journal of Molecular Cell Endomology 140,115-120.

Chen, P., T. J. Baas, J. W. Mabry, J. C. M. Dekkers, and K. J. Koehler. (2002). Genetic parameters and trend for lean growth rate and its components in U.S. Yorkshire, Duroc, Hampshire, and Landrace pigs. Journal of Animal Science, 80, 2062-2070.

Clowes, E. J., F. X. Aherne, A. L. Schaefer, G. R. Foxcroft, and V. E. Baracas. (2003). Parturition body size and body protein loss during lactation influence performance during lactation and ovarian function at weaning in first parity-sows. Journal of Animal Science, 81, I517-I528 (Abstr.).

Damgaard, L. H., L. Rydhmer, P. Lovendahl, and K. Grandison. (2003). Genetic parameters for within-Iitter variation in piglet birth weight and change in within-litter variation during suckling. Journal of Animal Science, 81, 604-610.

Fall, C. H. D., C. S. Yajnik, S. Rao, A. A. Davies, N. Brown, and H. J. W. Farrant. (2003). Micronutrients and fetal growth. Journal of Nutrition, 133 (Suppl.), 1747S-I756S.

Gibson, J. P., C. Aker, and R. Ball. (1998). Levels of genetic variation for growth, carcass and meat quality traits in purebred pigs. Proceedings ofthe 6th World Congress on Genetics Applied to Livestock Production. Vol. 23, 499-502. Armidole, NSW, Australia.

Giesemann, M. A., A. J. Lewis, P. S. Miller, and M. P. Akhter. (1998). Effects ofthe reproductive cycle and age on calcium and phosphoms metabolism and bone integrity of sows. Journal of Animal Science, 76, 796-807.

14

Gmffra, E., J. M. H. Kijas, V. Amarger, O. Carlborg, J. -T. Jeon, and L. Andersson. 2000. The origin ofthe domestic pig: independent domestication and subsequent infrogression. Genetics Society of America, 154, 1785-1791.

Grandinson, K. (2003). Genetic aspects of maternal ability in sows. Ph.D. Dissertation, Department, of Animal Breeding and Genetics. Swedish University of Agricultural Science, Sweden.

Hanka, R., L. Lawn, I. H. Mills, D. C. Prior, and P. M. Tweeddale. (1975). The effects of matemal hypercapnic and foetal oxygenation and uterine blood flow in the pig. Journal of Physiology 247, 447-460.

Honeyman, M. S., D. C. Lay Jr., and J. D. Harmon. (1999). Thermal stress levels of sows in various gestation housing systems (p. 172). ISU Swine Research Report, Management/Economics, Iowa State University, Ames, lA.

Kim, S. W., W. L. Huriey, I. K. Han, H. H. Stein, and R. A. Easter. (1999). Effect of nutrient intake on mammary gland growth in lactating sows. Journal of Animal Science, 77,3304-3315.

Knight, J. W., F. W. Bazar, W. W. Thatcher, and D. E. Franke. 1977. Conceptus development in intact and unilaterally hysterectomized-ovariectomized gilts: interrelations among hormonal status, placental development, fetal fluids and fetal growth. Journal of Animal Science, AA, 620.

Mahan, D. C , and J. L. Vallet. (1997). Vitamin and mineral transfer during fetal development and early postnatal period. Journal of Animal Science, 75, 2731-2738.

Merck Veterinary Manual. (1998). Merck Veterinary Manual. 8th ed. (pp. 1485-1495 and I599-I6I0). Merck & CO., Inc, Nat. Pub. Inc. Philadelphia, PN.

Moeller, S. J., J. W. Mabry, T. J. Boas, K. J. Stalder, and M. T. See. (2000). Genetic trend for reproductive traits in Hampshire swine. International Congress on Animal Reproduction., 1:304. (Abstr.). Stockholm, Sweden.

NRC. (1998). Nutrient Requirements of Swine 10th rev. ed. Nati. Acad. Press, Washington D.C.

Reynold, L. P., and D. A. Redmer. (1995). Utero-placental vascular development and ^\dicents\fw\c\.\on. Journal of Animal Science, 73, 1839-1851.

15

PorkBoard. (2000). Economic and Future Markets Report. Pork Check-off, National Pork Board.

Silva, P. F. N., A. M. Finch, C. Antipatis, and C. J. Ashworth. (2000). Changes in the relationship between porcine fetal size and organ development during pregnancy. Paper presented at British Society of Animal Science annual meeting.

Ullrey, D. E., J. L. Sprague, D. E. Becker, and E. R. Miller. (1965). Growth ofthe swine fetus. Journal of Animal Science, 24, 711-7I7.

Vallet, J. L., K. A. Leymaster, and R. K. Christenson. (2002). The influence of uterine function on embryonic and fetal survival. Journal of Animal Science, 80,(E. SuppL2),EI15-E125.

Wilson, M. E., N. J. Biensen, and S. P. Ford. (1999). Novel insight into the control of litter size in pigs, using placentail efficiency as a selection tool. Journal of Animal Science, 11, 1654-1658.

16

CHAPTER ni

FETAL GROWTH IN THE PIG:

NUTRITIONAL IMPLICATIONS

Abstract

Three hundred twenty fetuses from 33 gihs (Cambrough-22, PIC, Franklin, KY)

were used in this study to determine fetal growth and development during different days

of gestation. All the gifts were fed an equal amount (2.0 kg/d) ofthe gestation diet once a

day. Gilts were slaughtered in groups representing day of gestation: 45 (six gifts), 60

(four gilts), 75 (five gilts), 90 (three gilts), 102 (five gifts), and 110 (four gilts). Six

additional gifts were slaughtered on d 0 of gestation to provide baseline information.

Fetuses were dissected into individual tissues, including carcass, gastrointestinal tract

(GIT), liver, lung, heart, kidney, spleen (d 75+), and partial placental collection. All the

individual fresh tissues were weighed and regression equations were obtained to explain

the weight changes of individual tissues during gestation. The contents ofthe dry matter,

crude ash, crude protein, and cmde fat were measured to explain compositional changes

during gestation. Fetal carcass weights increased {P < 0.05, linear) as day of gestation

progressed. The GIT to fetal weight ratio weight to fetal weight increased {P < 0.05,

linear), whereas the liver to fetal weight ratio decreased {P < 0.05, quadratic) as day of

gestation progressed. Cmde ash content (%) ofthe fetal liver was higher (P < 0.05) on d

60 and 75 than on other days of gestation. Cmde protein content (%) in the fetal liver

17

decreased (P < 0.05, linear) as day of gestation progressed. Cmde fat content (%) in the

fetal liver was higher (P < 0.05) on d 102 and 110 of gestation than on d 90 of gestation.

Weight ofthe GIT increased (P < 0.05, linear) as day of gestation progressed. There was

no correlation between DM, CP or cmde fat content and day of gestation (P > 0.05),

indicating that day of gestation did not affect DM or CP content (%) ofthe fetal GIT.

Cmde ash content (%) ofthe fetal GIT had a tendency to decrease (P < 0.06, linear) as

gestation progressed.

From determining breakpoints ofthe slopes for fetal tissue growth, the growth

rate ofthe GIT is accelerated after d 56.3 of gestation, whereas the growth rate ofthe

liver is decelerated after d 63.2 of gestation. These data suggest that fetal tissue growth

occurs at varying days of gestation, indicating that fetal nutrient requirements may also

fluctuate, especially near d 60 of gestation.

Key Words: Fetus, Gestation, Growth, Pigs, Tissues

Introduction

It has been previously reported that fetal growth and development occurs at

various rates during gestation (Ullery et al., 1965; Silva et al., 2000; Wu et al., 1999).

Ullrey et al. (1965) characterized the growth of major fetal tissues in the pig, further

demonstrating that fetal tissue growth occurs at varying rates during gestation. There are

several factors that influence and regulate fetal growth and development. One such factor

that heavily influences these processes is matemal nutrition (Anthony et ah, 1995; Fall et

al, 2003; Alien, 2001).

Currently, it is unknown whether the sow receives enough nutrition throughout

gestation to adequately and efficiently supply nutrients to all the growing fetuses equally,

and in a manner that promotes optimal growth and development (Mahan et ah, 1997). It

has been previously demonstrated that advancements in improving the sow's nutrition

during gestation can have profound effects on increased birth weights, weaning weights,

and decreased piglet mortality, as well as showing posftive effects on retuming to estms

ofthe sow (Schoknecht, 1997; Yen et al., 1991). Feeding gestating sows is critical not

only to the development ofthe fetuses but also to the final milk production during

lactation (Schoknecht, 1997; Kim and Easter, 2003). Maximal feed intake is required

during lactation to have optimum mammary gland growth for increased milk production

(Kim et al., 1999; Kim and Easter, 2003), which will, in tum, improve weaning weight.

Tremendous advances have taken place over the past 40 yr in the swine industry,

including genetic improvement ofthe sow (Grandison, 2003); however, a better

19

understanding of fetal growth and development in today's swine herd is needed to further

improve neonatal and postnatal growth. Therefore, the objectives of this study were 1) to

characterize growth and development of fetal tissues; and 2) to characterize

compositional changes of fetal tissues.

Materials and methods

Animal Care and Use. An animal care and use protocol was approved, by the

Animal Care and Use Conmiittee of Texas Tech University (#02203).

Animals and Experimental Design. Thirty-three gilts (Cambrough-22, PIC,

Franklin, KY) producing a total of three hundred and twenty fetuses were used in this

study. Gilts were housed in individual standard gestation crates at the Texas Tech Swine

Research Farm (New Deal, TX). AU gilts were checked for heat once a day in the

moming and bred with non-frozen semen via artificial insemination by the farm staff

twice during an estrous cycle (18 to 24 h apart). Gilts were allowed to consume 2 kg/d of

gestation diet of (Table 3.1). Gilts were fed once a day in the moming and had free

access to water throughout the entire sttidy. Each ofthe gifts was assigned to one of six

slaughter groups representing various set days of gestation. Six gifts were slaughtered on

d 0 (prior to breeding) to obtain base line information about the uterus. Six gifts were

slaughtered on d 45 (44 to 48), four gifts were slaughtered on d 60 (59 to 61), five gifts

were slaughtered on d 75 (75 to 76), three gilts were slaughtered on d 90 (90 to 92), five

20

gifts were slaughtered on d 102 (101 to 104), and four gilts were slaughtered on d 110

(107 to 112) (Table 3.2).

Diet Soybean meal was used as a major protein source and com was used as a

major energy source in the diet, providing 89.2% DM, 12.2% CP, 0.56% lysine, 3.1

Mcal/kg ME, and 0.94% Ca (Table 1).

Slaughter. Gifts were transported to the Texas Tech Meat Laboratory (Lubbock,

TX) in the evening before to slaughter, where they were withheld from feed. The gifts

were weighed and then slaughtered in the moming, in compliance with the Texas Tech

Meat Laboratory Standard Operating and Procedures Protocol for the Slaughter of Swine.

Sample Collection The entire reproductive tracts were collected during the

slaughter process. Weights ofthe entire reproductive tracts were taken. The utems was

then placed on a table and the uterine membrane was removed allowing for both homs to

be spread out, to measure the length of each hom. Each hom represented either the long

side (L) or short side (S). The fetuses were separated from the uterine hom by cutting the

placenta at the base ofthe amniotic sac and then again at the base ofthe umbilicus.

Fetuses were weighed as a whole and further dissected via a medial incision to expose

individual organs. The heart, liver, lung, gastrointestinal tract (GIT), kidneys, and spleen

were collected via blunt dissection. The spleens were collected from the fetuses only after

d 75 of gestation because it was not clearly visible before d 75 of gestation. Partial

placental collection was obtained for a chemical analysis. Whole placentas were not

obtained due to mpture during carcass processing. The weights of all fetal tissues as

21

well as tiie fetal carcasses, were recorded. Fetal brains were collected and weighed

on samples greater than d 45 of gestation.

Sample Drying, After the weights were recorded, the individual samples were

stored in the -20°C freezer. Fetal samples from the (S) side were taken from the -20°C

freezer and incompletely thawed in a 4°C refrigerator for 2 to 6 h. Samples from the same

gift were pooled by tissue. The pooled carcass and pooled individual tissues were then re-

weighed. The samples were then placed in a freeze dryer (TD44-0 Dura-Top Freeze

Dryer, FTS Systems, Chatswood, New South Wales) until fully dried (approximately 7 to

14 d). The dried samples were then weighed and ground with a standard laboratory size

grinder.

Chemical Analvsis. The DM, ash, cmde fat, and CP content were determined (for

fetal carcass, liver, GIT, placenta, and brain). Dry matter content was determined by the

desiccation ofthe tissue at 105°C for 4 h in a forced air oven. Cmde protein content (N

X 6.25) was determined using a combustion method (LECO FP 2000, Leco Corp., St.

Joseph, MI). Cmde fat was determined from dried tissue, using the Soxhlet extraction

method, using petroleum ether binary extracting solution (Novakofski et ah, 1989). Ash

was measured by the combustion of dried tissue at 500°C for 8 h. Chemical analysis was

not done for samples from d 45 of gestation including the fetal GIT, heart, brain, and

kidney due to limited sample size. Cmde fat content (%>) was not measured for the fetal

liver on d 45 of gestation, or for the fetal liver and brain on d 60 of gestation, or for the

fetal liver on d 75 of gestation due to limited sample size.

22

Statistical analvsis. Statistical analysis was performed using a completely

randomized design with a general linear model procedure (PROC GLM) of SAS (SAS

Inst. INC., Cary, NC). The sow was used as an experimental unit. The mean was

modeled using day of gestation as the main effect. Standard errors and least squared

means were obtained from the model. The regression procedure (PROC REG) was used

to describe the quantitative changes of each tissue as day of gestation progressed. The

NLREG software was used to obtain the breakpoint from the multi-phasic regression

(Sherrod, 1992) for fhe liver:fetal weight ration and the GIT:fetaI weight ratio.

Results

Individual tissues

Fetal carcass. Fetal carcass weight increased (P < 0.05, linear) as day of gestation

progressed (Table 3.3). The highest (P < 0.05) fetal carcass weights were observed on d

102 and d 110 of gestation (Table 3.3). Dry matter (%) ofthe fetal carcass was higher (P

< 0.05) on d 102, than on d 75 of gestation (Table 3.3). However, there was no

correlation between DM content (%) and day of gestation (P > 0.05), indicating that day

of gestation did not affect DM (%) ofthe fetal carcass (Table 3.3). Cmde ash content (%)

ofthe fetal carcass was higher (P < 0.05) on d 60 and 75, than on d 45, 90, 102, and 110

of gestation (Table 3.3). However, there was no correlation between cmde ash content

(%) and day of gestation (P > 0.05) indicating that day of gestation did not affect cmde

ash content (%) ofthe fetal carcass (Table 3.3). Crude protein content (%) ofthe fetal

23

carcass was higher (P < 0.05) on d 45 and 60 than on d 110 of gestation (Table 3.3), and

CP (%) ofthe fetal carcass decreased (P < 0.05, linear) as gestation progressed (Table

3.3). Crude fat content (%) ofthe fetal carcass was higher (P < 0.05) on d 45 than on d

75 and 110 of gestation (Table 3.3). However, there was no correlation between cmde fat

content (%) and day of gestation (P > 0.05), indicating that day of gestation did not affect

cmde fat content (%>) ofthe fetal carcass (Table 3.3).

Fetal brain Chemical analysis was measured with fetal brain samples collected

on d 60, 75, 90, 102, and 110 of gestation due to limited size ofthe sample. Cmde fat

content (%) was measured on d 75, 90, 102, and 110 of gestation. Fetal brain weight

increased (P < 0.05, linear) as day of gestation progressed (Table 3.4). The highest (P <

0.05) fetal brain weight was observed on d 110 of gestation (Table 3.4). Dry matter

content (%) ofthe fetal brain had a tendency to be higher (P < 0.07) on d 75 than on other

days of gestation (Table 3.4). However, there was no correlation between DM content

(%) and day of gestation (P > 0.05), indicating that day of gestation did not affect DM

content (%>) of the fetal brain (Table 3.4). Cmde ash content (%) of the fetal brain

decreased (P < 0.05, linear) as day of gestation progressed (Table 3.4). Crude protein

content (%) ofthe fetal brain was higher (P < 0.05) on d 60 than on d 75, 90, 102, and

110 of gestation (Table 3.4). However, there was no correlation between CP content (%)

and day of gestation (P > 0.05), indicating that day of gestation did not affect CP content

(%) ofthe fetal brain (Table 3.4). There was no correlation between cmde fat content (%)

24

and day of gestation (P > 0.05), indicating that day of gestation did not affect cmde fat

content (%) ofthe fetal brain (Table 3.4).

Fetal GIT. Chemical analysis was measured with fetal GIT sample collected on

d 60, 75, 90, 102, and 110 of gestation due to limited size ofthe sample. Fetal GIT

weight increased (P < 0.05, linear) as day of gestation progressed (Table 3.5). The

highest (P < 0.05) fetal GIT weight was observed on d 102 and 110 of gestation (Table

3.5). There was no correlation between DM content {%) and day of gestation (P > 0.05),

indicating that day of gestation did not affect DM (%) content ofthe fatal GIT (Table

3.5). Cmde ash content (%) ofthe fetal GIT was higher (P < 0.05) on d 60 and 75 than

on d 90, 102, and 110 of gestation (Table 3.5). Crude ash content (%) ofthe fetal GIT had

a tendency to decrease (P < 0.06, linear) as gestation progressed (Table 3.5). There was

no correlation between CP content (%) and day of gestation (P > 0.05), indicating that

day of gestation did not affect CP (%) ofthe fetal GIT (Table 3.5). There was no

correlation between cmde fat content {%) and day of gestation (P > 0.05), indicating that

day of gestation did not affect cmde fat content (%>) ofthe fetal GIT (Table 3.5)

Fetal heart. Chemical analysis was measured with fetal heart samples collected

on d 60, 75, 90, 102, and 110 of gestation due to limited size ofthe sample. Fetal heart

weight had a tendency to increase (P < 0.07, linear) as day of gestation progressed (Table

3.6). The highest (P < 0.05) fetal heart weight was observed on dl02 of gestation (Table

3.6). Dry matter content (%) ofthe fetal heart was higher (P < 0.05) on d 110, than on d

75 of gestation (Table 3.6). However, there was no correlation between DM content (%)

25

and day of gestation (P > 0.05), indicating that day of gestation did not affect DM content

(%)) ofthe fetal heart (Table 3.6). Crude ash content (%) ofthe fetal heart was higher (P

< 0.05) on d 60 than on d 102 and 110 of gestation (Table 3.6). Cmde ash content (%) of

the fetal heart decreased (P < 0.05, linear) as day of gestation progressed (Table 3.6).

Cmde protein content (%) ofthe fetal heart was higher (P < 0.05) on d 102 than on d 75

of gestation (Table 3.6). However, there was no correlation between CP content (%) and

day of gestation (P > 0.05), indicating that day of gestation did not affect CP (%) ofthe

fetal heart (Table 3.6).

Fetal liver Cmde fat content was measured on d 90, 102, and 110 of gestation

due to limited size ofthe sample. Fetal liver weight increased (P < 0.05, linear) as day of

gestation progressed (Table 3.7). The highest (P < 0.05) fetal liver weight was observed

on d 90, 102, and 110 of gestation weight (Table 3.7). There was no correlation between

DM content (%) and day of gestation (P > 0.05), indicating that day of gestation did not

affect DM content (%) ofthe fetal liver (Table 3.7). There was no correlation between

cmde ash content (%) and day of gestation (P > 0.05), indicating that day of gestation did

not affect cmde ash content (%) ofthe fetal liver (Table 3.7). Cmde protein content (%)

ofthe fetal liver was higher (P < 0.05) on d 45, 60, 75, and 102 than on d 110 of gestation

(Table 3.7). Cmde protein content (%) ofthe fetal liver decreased (P < 0.05, Ihiear) as

day of gestation progressed (Table 3.7). Cmde fat content (%) ofthe fetal liver was

higher (P < 0.05) on d 102 and 110 of gestation than on d 90 of gestation (Table 3.7).

However, there was no correlation between cmde fat content (%) and day of gestation (P

26

> 0.05), indicating that day of gestation did not affect cmde fat content (%) ofthe fetal

liver (Table 3.7).

Fetal lung. Fetal lung weight increased (P < 0.05, linear) as day of gestation

progressed (Table 3.6). The highest (P < 0.05) fetal lung weight was observed on d 90,

102, and 110 of gestation (Table 3.8). There was no correlation between DM content (%)

and day of gestation (P > 0.05), indicating that day of gestation did not affect DM content

(%)) of tiie fetal lungs (Table 3.8). Cmde ash content (%) ofthe fetal lungs was higher (P

< 0.05) on d 60 than on d 90 and 102 of gestation (Table 3.8). Cmde ash content (%) of

the fetal lungs decreased (P < 0.05, linear) as day of gestation progressed (Table 3.8).

Grade protein content (%>) ofthe fetal lungs was higher (P > 0.05) on d 45 than on d 60,

75, 90, 102, and 110 of gestation (Table 3.8). However, there was no correlation between

CP content (%) and day of gestation (P > 0.05), indicating that day of gestation did not

affect CP (%) ofthe fetal lung (Table 3.8).

Fetal placenta Dry matter content (%) of the fetal placenta was higher (P < 0.05)

on d 90 than on d 45 and 102 of gestation (Table 3.9). However, there was no correlation

between DM content (%>) and day of gestation (P > 0.05), indicating that day of gestation

did not affect DM content (%) ofthe fetal placenta (Table 3.9). Cmde ash content (%) of

the fetal placenta was higher (P < 0.05) on d 45 and 60 than on d 75, 90, 102, and 110 of

gestation (Table 3.9). Cmde ash content (%) ofthe fetal placenta decreased (P < 0.05,

logarithmic) as day of gestation progressed (Table 3.9). Cmde protein content (%) ofthe

fetal placenta was higher (P < 0.05) on d 60, 75, 90, and 102 than on d 45 of gestation

27

(Table 3.9). However, there was no correlation between CP content (%) and day of

gestation (P > 0.05), indicating that day of gestation did not affect CP content (%) ofthe

fetal placenta (Table 3.9).

Fetal kidneys. Chemical analysis was observed on d 60, 75, 90, 102, and 110 of

gestation due to limited size ofthe sample. Fetal kidney weight had a tendency to

increase (P < 0.06, linear) as day of gestation progressed (Table 3.10). The highest (P <

0.05) fetal kidney weight was observed on d 102 and 110 of gestation (Table 3.10).

There was no correlation between DM content (%) and day of gestation (P > 0.05),

indicathig that day of gestation did not affect DM content (%) ofthe fetal kidneys (Table

3.10). Cmde ash content (%) ofthe fetal kidneys was higher (P < 0.05) on d 60 than on d

75, 90, 102, and 110 (Table 3.10). Cmde ash content (%) ofthe fetal kidneys had a

tendency to decrease (P < 0.06, linear) as day of gestation progressed (Table 3.8). Cmde

protein content (%) ofthe fetal kidneys was higher (P < 0.05) on d 90 than on d 60 (Table

3.10). However, there was no correlation between CP content (%) and day of gestation

(P > 0.05), indicating that day of gestation did not affect protein content ofthe fetal

kidneys (Table 3.10).

Results of this study suggest that the growth of fetal tissues does not occur

uniformly during gestation. Based on tissue growth, the gestation cycle may be broken

into phases to better provide for all tissue growth.

28

Discussion

ft has been indicated that the gestating sow may have a period of increased need

for certain minerals and vitamins, though the exact time is not known (Mahan and Vallet,

1997). This could imply that feeding gestating sows may be broken into phases

depending on matemal nutrient need and availability. Gestation phases could be devised

by investigating when major fetal organ development occurs, in order to answer when

matemal nutrients need to be adjusted to properly support fetal growth.

Phases of gestation were determined based on individual organ growth as a

proportion to total fetal weight. When investigating the proportion of fetal GIT to fetal

weight, ft was observed that the proportion of fetal GIT increased linearly as gestation

progressed (Figure 3.1). However, this linear regression was able to be further broken

into two phase by the NLREG statistical analysis program. Obtaining a two phase

regression provided a reflection point where the slopes ofthe two phases met. This two

phase regression showed that the majority of fetal GIT growth occurs during the later

stages of gestation. The point in which fetal GIT growth accelerates was found to occur

after d 56.3 of gestation.

The changes ofthe fetal liver to fetal weight ratio, and fetal GIT to fetal weight

ratio were investigated to determine when the growth rate in of these tissues changed.

Using the same procedure, the point in which fetal liver growth deceleration, was found

to be after d 63.2 of gestation (Figure 3.1).

29

ft is practical to say tiaat the fetal GIT growth occurs mostly after d 56.3 of

gestation. The purpose ofthe digestive system is to breakdown foodstuffs into

absorbable and usable nutrients (Reece, 1997). The fetus utilizes matemal nutrients

which are supplied by the mother via the placenta (Reynolds and Redmer, 1995).

Therefore, the authors hypothesized that because there is no need for the fetus to supply

its own nutrients, the fetal GIT is relatively unused during the early stage of gestation.

However as parturition nears the fetal GIT growth accelerates in anticipation of supplying

nufrients to the new bom piglet.

Fetal liver growth occurs rapidly in the early stages of fetal growth and slows as

fetal growth progresses (Dyce et a l , 1996). The findings in this study also indicate that

the fetal liver growth mostly occurs before d 63 of gestation. One explanation for this

rapid growth occurring early in gestation is that increased erythropoietic activity taking

place within the liver (Dyce at al., 1995; Reece 1997). During prenatal growth, the

formation of erythopoiesis occurs in the liver, spleen, and bone marrow; whereas during

postnatal growth, erythopoiesis formation is almost exclusively produced in the bone

marrow (Reece, 1997). The liver continued to decrease in proportion to fetal weight as

gestation progressed (Table 3.7). This implies that the liver has a decreasing role as the

fetal development progresses.

The placenta undergoes two physiological changes during gestation. As the

uterine swelling changes; from pear-shaped (20 d), to spherical-shaped (25 d), and lastly

to ovoid -shaped (30 d), the uterine tissues thicken and the allantoic sac rapidly expands

30

to keep up with the changing uterine environment. These changes result in the change of

the primary choriovitelline (yolk sac) placentation developing into the chorioallantoic

placentation (Evans, 1993). This is also a critical time in the development ofthe fetus. It

has been shown that fetuses undergo increased stress during this time (Evans, 1993).

During the later states of gestation, placental growth slows or ceases (Reynolds and

Redmer, 1995). Fetal growth increases exponentially (Reynolds and Redmer, 1995; NRC,

1998), which is also concurrent with the findings of this study (Figure 3.2). Wu et al.,

(1999) reported that fetal growth is greatest at the last 4 days of gestation. This indicates

that the placental-fetal relationship is heightened at the later stages of gestation, as the

placenta still serves to provide the growing fetus with needed matemal nutrients.

To characterize fetal growth and development, Ullrey et al. (1965) investigated

fetal growth at d 30, 51, 72, and 93 of gestation and at birth. These data established a

basis for fetal growth in the sow used in the mid-1960s. However, today's sows have

changed considerably over the decades, as have the management practices. Today's sow

is leaner and more efficient, thus ft is rational to believe that fetal development has also

changed as the sow is genetically modified.

UUrey et al. (1965) collected pigs at birth, this study collected fetuses at d 110 of

gestation, which represented farrowing. When comparing brain weight with the data

collected from Ullrey (1965) ft was found that Ullrey et al. (1965) observed a higher

brain weight at birth (35.1 g/pig) (Table 3.11) than this study (25.5 g/fetus) (Table 3.4).

31

Ullrey et al. (1965) also observed a higher fetal liver weight at birth (24.9 g pig)

(Table 3.11), than from this study (19.2 g/fetus) at d 110 of gestation (Table 3.7).

However, the data in this study indicated that the fetal liver (Table 3.7) was heavier than

the fetal liver in 1965 (Table 3.11). An increased fetal liver weight could represent a

higher level of liver function in today's fetal pig.

Improving fetal development by improving the matemal nutrient supply has been

an ongoing task. It is known that the delivery of available nutrients by the utems to the

developing fetuses directly impacts growth, development and survivability (Vallet et al.,

2002). Even with today's advancements in the sow, it has been predicted that 30 to 40%

of potential piglets die before the farrowing date (Vonnahme et al., 2002). When

establishing new nutrient requirements for the gestating sow, organ development must be

taken into consideration. Based on the proportional changes ofthe fetal liver and the

fetal GIT, matemal nutrient need for maximal fetal growth may be different before and

after d 60 of gestation.

Implications

The growth of fetal tissues occurred by different degrees as well as at different

times of gestation which affect the amount and composftion of nutrients needed by the

sow to support thefr growth. By considering the matemal nutrient needs for optimal fetal

tissue growth; feeding the gestating sow can be based on a two distinct phases; d 0 to 60

of gestation and d 60 of gestation to farrowing.

32

Table 3.1 Composition of gestation diet.

Ingredient

Com grain, yellow Soybean meal, de-huUed Molasses cane Potassium chloride'^ Salt Vitamin-mineral premix ̂ Oil, vegetable Dicalcium phosphate Limestone Alfalfa meal Total Calculated composition Dry matter, %> ME, Mcal/kg Cmde protein, % Lysine, % Cystine + Methionine, %> Tryptophan, %o Thereonine, % Calcium, % Available phosphoms, %

Total phosphoms, %

% as fed

72.45 11.00 5.00 0.25 0.35 1.50 0.50 2.20 0.50 5.00

100.00

89.20 3.10

12.20 0.56 0.44 0.13 0.45 0.94 0.47

0.69 'DYNA K POT CHL (IMC Globle, Lake forest, Illinois). ^ Vftamin-mineral premix provided the following per kilogram of complete diet: 23.3 mg manganese as manganous oxide, 37.5 mg iron as iron sulfate, 51.9 mg zinc as zinc oxide, 4.7 mg copper as copper oxide, 0.36 mg iodide as ethylenediamine dihydroiodide, 0.1 Img selenium as sodium selenite, 3777.8 IU vitamin A as vitamin A acetate, 412.5 IU vitamin D3, 31 IU vftamin E, 1.4 IU vitamin K as menadione sodium bisulfate, 27.5 pg vitamin B12, 6.9 mg riboflavin, 22 mg D-pantothenic acid as calcium pantothenate, 27.5 mg niacin and 828.8 mg choline as choline CI.

33

Table 3.2 The number of gilts used per day of gestation and the number of fetuses collected

Number of gilts

Number of fetuses

0

6

0

45

6

79

Day of

60

4

54

gestation

75

5

50

90

3

33

102

5

65

110

4

39

34

Table 3.3 Chemical composition, on a percent dry matter basis, ofthe fetal carcass on different days of gestation

Day of gestation

45 60 75 90 102 110 SEM'

Weight, 13.82' 102.75'' 133.91'' 475.61' 718.82^ 899.72^ 82.18

g/fetus''

Dry matter, % 22.50"* 25.15"' 20.20' 29.23"* 31.32'* 25.52"* 0.13

Cmde ash, % 17.07' 21.49'* 24.07'* 17.83' 17.03' 17.16' 0.83

Cmde protein, 63.94' 60.41' 57.44^* 59.09'* 57.93** 51.08' 1.03

%s

Cmde fat, % 15.97' 15.13' 11.67** 14.40"* 14.01"* 12.44** 1.33 ''Pooled standard error ofthe mean. *' Within a row, linear relationship, among the means, observed as gestation progressed (P < 0.05, r̂ = 0.91). "*'*"Within a row, means that do not have a common superscript letter differ (P < 0.05). ^Within a row, linear relationship, among the means, observed as gestation progressed (P < 0.05, r̂ = 0.73).

35

Table 3.4 Chemical composition, on a percent dry matter basis, ofthe fetal brain on different days of gestation

45

Day of gestation

60 75 90 102 110 SEM'

Weight, g/fetus*'

Dry matter, %

Cmde ash, Vo^

3.13' 3.57' 9.88"* 17.45** 25.46' 2.15

18.12 26.35 19.08 18.85 17.95 0.24

cd 11.82' 10.96' 9.46'*" 7.28" 8.30'*̂ 0.46

Cmde protein, %

Grade fat, %

63.23' 58.59" 58.90" 59.11" 58.44** 0.46

31.34 30.49 30.48 32.22 2.40

'Pooled standard error ofthe mean. ^ Within a row, linear relationship, among the means, observed as gestation progressed (P < 0.05, r̂ = 0.88). '**' Within a row, means lacking a conunon superscript letter differ (P < 0.05). ^ Within a row, linear relationship, among the means, observed as gestation progressed (P

< 0.05, r̂ = 0.88).

36

Table 3.5 Chemical composition, on a percent dry matter basis, ofthe fetal gastrointestinal tract on different days of gestation

Day of gestation

45 60 75 90 102 110 SEM'

Weight, 3.45" 7.89" 36.77' 49.62' 52.72' 5.41 g/fetus''

Dry matter, % 20.48 16.10 21.91 17.97 23.20 0.14

Grade ash, %^ 9.26' 8.62' 8.3l" 8.49" 8.28" 0.14

Grade 72.10 70.89 71.00 71.15 72.79 0.39 protein, %

Cmde fat, % 15.33 15.44 15.23 14.61 13.11 1.49

'Pooled standard error ofthe mean. ^ Within a row, linear relationship, among the means, observed as gestation progressed (P < 0.05, r2 = 0.95). '"' Within a row, means that do not have a common superscript letter differ (P < 0.05). *" Within a row, linear frend, among the means, observed as gestation progressed (P <

0.06, r̂ = 0.75).

37

Table 3.6 Chemical composition, on a percent dry matter basis, ofthe fetal heart on different days of gestation

Weight, g/fetus*'

Dry matter, %

Grade ash, %'

Crude protein, %

' Pooled standard

45

error ofth *' Within a row, linear trend. 0.07, r̂ = 0.72).

60

0.83'

21.49'"

7.56'

77.37'"

e mean. among the

Day of

75

4.46'"

16.40'

6.61'"

71.10'

means.

gestation

90

5.66'"

23.01'"

6.76'"

76.82'"

observed as

102

7.13"

19.56'"

6.33"

77.87"

gestation

110

5.36'"

25.75"

6.31"

76.89'"

SEM'

0.91

0.13

0.14

0.89

progressed (P <

'" Within a row, means that do have a common superscript letter differ (P < 0.05). ' Within a row, linear relationship, among the means, observed as gestation progressed (P < 0.05, r̂ = 0.78).

38

Table 3.7 Chemical composition, on a percent dry matter basis, ofthe fetal liver on different days of gestation

Day of gestation

45 60 75 90 102 110 SEM'

Weight, 1.36' 7.44' 9.37' 23.52" 21.87" 19.22" 1.90

g/fetus''

Dry matter, 23.52 26.44 20.89 31.72 25.03 29.42 0.13 %

Grade ash, 8.33 7.61 6.75 6.23 8.42 8.28 0.42 %

Cmde 75.83' 78.94' 78.95' 72.21'" 67.58'" 58.38" 1.89 protein, %'

Cmde fat, % 19.46' 16.55' 24.80" 1.48

'Pooled standard error ofthe mean. *' Within a row, linear relationship, among the means, observed as gestation progressed (P < 0.05, r̂ = 0.83) '" Within a row, means that do not have a common superscript letter differ (P < 0.05). ' Within a row, linear relationship, among the means, observed as gestation progressed (P < 0.05, ^ = 0.66).

39

Fable 3.8 Chemical composition, on a percent dry matter basis, ofthe fetal lung on different days of gestation

Day of gestation

45 60 75 90 102 110 SEM'

Weight, 0.31' 4.43' 6.91' 22.94" 26.86" 25.42" 2.59

g/fetus*'

Dry matter, 25.43 20.13 24.02 19.89 18.04 26.59 0.18 %

Grade ash, 8.43" 8.52' 7.66'" 6.78" 7.1l" 7.28'" 0.22

Cmde 75.01' 65.10" 62.73" 69,38' 69.55' 70.38' 0.91 protein, %

'Pooled standard error ofthe mean. *' Within a row, linear relationship, among the means, observed as gestation progressed (P < 0.05, r̂ = 0.91). '"' Within a row, means that do not have a common superscript letter differ (P < 0.05). *" Within a row, linear relationship, among the means, observed as gestation progressed (P

< 0.05, r̂ = 0.73).

40

Table 3.9 Chemical composition, on a percent dry matter basis, ofthe fetal placenta on different days of gestation

Day of gestation

45 60 75 90 102 110 SEM'

Dry matter, 14.98' 19.99'" 19.35'" 26.40" 15.44' 19.32'" 0.14 %

Cradeash, 12.37' 11.02' 8.94" 9.52" lO.Ol" 9.56" 0.29 % '

Cmde 69.96' 74.29" 74.80" 74.29" 73.33" 72.41'" 0.91 protein, %

' Pooled standard error of the mean. '" Within a row, means that do not have a common superscript letter differ (P < 0.05). ' Within a row, logarithmic trend, among the means, observed as gestation progressed (P < 0.06, r̂ = 0.65).

41

Table 3.10 Chemical composition, on a percent dry matter basis, ofthe fetal kidneys on different days of gestation

Day of gestation

45 60 75 90 102 110 SEM'

Weight, g/fetus^ 10.97' 17.04'" 40.40"' 56.24' 39.40' 4.93

Drymatter,% 21.25 19.23 23.13 17.89 24.97 0.14

Cmde ash, %^ 9.11' 7.25"' 7.40" 7.13"' 6.59' 0.20

Grade protein, 71.92' 73.28'" 74.82" 74.24'" 72.98'" 0.38 0 /

'Pooled standard error ofthe mean. '' Within a row, linear trend, among the means, observed as gestation progressed (P < 0.06, r̂ = 0.76). '"' Within a row, means that do not have a common superscript letter differ (P < 0.05). ^ Within a row, linear trend, among the means, observed as gestation progressed (P < 0.06, r^= 0.76).

42

Fable 3.11. Weights ofthe fetal tissues on different days of gestation'

Day of gestation

51 72 93 Birth

Brain, g/fettis 1.98 ±0.06 9.25 ±0.12 22.30 ±0.76 35.08 ±0.65

Heart, g/fetus 0.42 + 0.01 1.56 ±0.05 4.07 ±0.11 6.90 ±0.48

Lungs, g/fetus 1.22 ±0.05 6.00 ±0.22 16.89 ±0.65 17.09 ±1.60

Liver, g/fetus 3 .26±0.16 6.44±0.23 14.18±0.51 24.90±2.90

Spleen, 17.5 ±1.0 200.1 ±9.0 832.8 ±37.0 781.0 ±66.0

mg/fetus

Kidneys, g/fetus 0.37 ±0.02 1.08 ±0.04 2.34 ±0.08 3.64 ±0.334

'Partial recreation of data collected by UUrey et al. (1965), showing weights (g) of fetal tissues, moisture included, during gestation.

43

7t

o o

Day of gestation

- Fetal liver -Ar Fetal GIT

Figure 3.1 The fetal GIT to fetal weight ration (%) increased (P < 0.05, linear) as day of gestation progressed (y = 0.0579 x - 0.3157, r̂ = 0.99). The fetal liver to fetal weight ration (%) decreased (P < 0.05, quadratic) as day of gestation progressed (y = 0.0027 x -0.5388 X + 29.224, r̂ = 0.97, where x = day of gestation and y = proportion of fetal wt, %).

44

1,600 2 1,400 § 1,200 I 1,000

800 H 600 400 ̂ 200 0

C3

iil i

45

i

60 75 90

Day of gestation

1 I

102 110

Figure 3.2 Whole fetal weight increased (P < 0.05, exponential) as day of gestation progressed (y = 0.8107 x 6"+ 18.382, r̂ = 0.90, where y = whole fetal weight (g), and x day of gestation).

45

Literature Cited

Allen, L. H. 2001. Biological mechanisms that might underiie iron's effects on fetal growth and preterm birth. Journal of Nutrition, 131, 581S-589S.

Antiiony, R. V., S. L. Pratt, R. Liang, and M. D. Holland. 1995. Placental-fetal hormonal interacfrons: impact on fetal growth. Journal of Animal Science, 73, 1861-1871.

Dyce, K. M., W. O. Sack, and C. J. G. Wesing. (1996). Textbook of Veterinary Anatomy (pp. 146-147). 2nd ed. W. B. Saunders Co. Philadelphia, PA.

Evans, H. E. (1993). Millers Anatomy ofthe Dog (3rd ed.) (pp 37). W. B. Saunders Co Philadelphia, PA.

Fall, C. H. D., C. S. Yajnik, S. Rao, A. A. Davies, N. Brown, and H. J. W. Farrant. 2003. Micronutrients and fetal growth. Journal of Nutrition, 133, 1747S-1756S.

Kim, S. W. and R. A. Easter. (2003). Amino Acids in Animal Nutrition. Amino acid utilization for reproduction in sows (pp. 203-222), CAB Intemational (2nd ed.) T P. F. D Mello.

Kim, S. W., W. L. Hurley, I. K. Han, H. H. Stein, and R. A. Easter. (1999). Effect of nutrient intake on mammary gland growth in lactating sows. Journal of Animal Science, 77,3304-3315.

Mahan, D. C , and J. L. Vallet. (1997). Vftamin and mineral fransfer during fetal development and the early postnatal period in pigs. Journal of Animal Science, 75,2731-2738.

NRC. (1998). Nutrient Requirements of Swine, 10th rev. ed. The National Academy Press, Washington D.C.

Reece, W. O. (1997). Physiology of Domestic Animals, (pp. 270-271). Williams and Wilkins. Baltimore, MD. USA.

Reynolds, L. P., and D. A. Redmer. (1995). Utero-placental vascular development and placental function. Journal of Animal Science, 73, 1839-1851.

Schoknecht, P. A. (1997). Swine nutrition: nutrient usage during pregnancy and early postnatal growth, an introduction. Journal of Animal Science, 75, 2705-2707.

46

5herrod, P. H. (1992). NLREG. Nonlinear Regression Analysis Program. Nashville, TN.

JUrey, D. E., J. L. Sprague, D. E. Becker, and E. R. MiUer. (1965). Growth ofthe swine fetus. Journal of Animal Science, 24, (No. 3) 711-717.

>/aUet, J. L., K. A. Leymaster, and R. K, Christenson. (2002). The influence of uterine fimction on embryonic and fetal survival. Journal of Animal Science, 80 (E. SuppI.),E115-E125.

Vonnahme, K. A., M. E. Wilson, G. R. Foxcroft, and S. P. Ford. (2002). Impacts on conceptus survival in a commercial swine herd. Journal of Animal Science, 11, 1654-1658.

Wu, G., T. L. Ott, D. A. Knabe, and F. W. Bazer. 1999. Amino acid composition ofthe fetal pig. Journal of Nutrition, 129,1031-1038.

Yen, J. T., G. L. Cromwell, G. L. Allee, C. C. Calvert, T. D. Crenshaw, and E. R. Miller. 1991. Value of raw soybeans and soybean oil supplementation in sow gestation and lactation diets: a cooperative study. Journal of Animal Science, 69, 656-663.

47

CHAPTER IV

LITTER CHARACTERISTICS AND INTRAUTERINE LOCATION

IN RELATION TO FETAL GROWTH AND

DEVELOPMENT IN THE PIG

Abstract

Three hundred twenty fetuses from 33 gifts (Cambrough-22, PIC, Franklin, KY)

were used in this study to determine fetal growth as related to fetal location within the

uterine hom during gestation, and to determine when litter weight variation occurs during

gestation. All gilts were fed (2.0 kg/d) on an as fed basis, ofthe same gestation diet. Gilts

were assigned to slaughter groups representing various days of gestation: d 45 (six gilts),

60 (four gilts), 75 (five gifts), 90 (three gifts), 102 (five gilts), and 110 (four gilts). At

slaughter, the reproductive tracts were obtained from all the gifts and dissected to obtain

the fetuses. Before the dissection, the location of each fetus was recorded with the

cranial-most extremfty of each hom being location number one and the cervical-most

extremity being the last location. Regression equations were obtained to explain the

weight changes of individual tissues as uterine location proceeded cranial to cervical.

Fetal weights decreased (P < 0.05) linearly as uterine location ofthe fetus proceeded

cranial to cervical, when the data were pooled regardless of day of gestation in the

statistical analysis. When the data were analyzed by day of gestation, fetal weights

decreased (P < 0.05) lineariy as uterine location ofthe fetus proceeded cranial to cervical

48

n d 60 and 102 of gestation. Fetal weight variation among littermates was higher (P <

L05) on d 75 and 102 than on other days of gestation. This study suggests that the sows

ail to supply enough nutrients to all the fetuses in a litter, which causes weight

lifferences on d 60 and 102 by fetal location, as well as d 75 and 102 of gestation

egardless of fetal location. In conclusion, the sows may have a limited capacity to

lupply enough nutrients to their fetuses after d 60 of gestation.

<Cey words: Fetus, Pigs, Uterine Location, Weight.

49

Introduction

The endomefrium lining tiie interior ofthe uterus is extremely glandular. The

glandular secretions from the edometrium supply the fetuses with nutrients before

placentation occurs (Reece, 1997). After placentation, the matemal blood supply

provides nutrients to the developing fetuses (Reece, 1997); ft is at the stage in which the

nother beings to supply the nutrients to the fetuses that is of cmcial importance. The sow

supplies the developing fetuses with a single branching artery (Merck, 1998). Currently,

it is not known how the mother distributes the nutrients or if she is receiving enough

ttutrients to adequately provide for all of the fetal nutrient requirements (Mahan and

Vallet, 1997). The modem swine herd is being selected for larger litter size; however,

with this breeding selection, it has been found that birth weight decreases as litter size

mcreases (Johnson, 1999). Finding when matemal nutrient need increases during

gestation will allow for better feeding strategies to be implemented to promote for

increased birth weights.

Piglet birth weight is an indicator of fiiture piglet performance up to the weaning

stage (Allyson et al., 2001). A limited nutrient supply to the fetuses in different locations

within the uterine hom may cause differing growth rates and in tum, may lead to weight

variation at birth. Birth weight variations among littermate's leads to an increased

mortality rate (Wise et ah, 1997). Identifying the stage of gestation when litter weight

variation occurs can be critical information when determining proper maternal nufrient

50

intake. Therefore, objective of tills study was to 1) investigate the relationship between

tiie mfrauterine location and fetal tissue growth during different stages ofthe gestational

cycle; and 2) identify when litter weight variation occurs during gestation.

Materials and methods

Animal Care and Use. The animal care protocol (# 02203) was approved for this

study by the Animal Care and Use Committee at Texas Tech University, Lubbock, TX.

Animals and Experimental Design. A total of three hundred twenty fetuses

collected from thirty-three gifts (Cambrough-22, PIC, Franklin, KY) were used in this

study. Gilts were housed in individual standard gestation crates at the Texas Tech Swine

Research Farm (New Deal, TX). All gilts were checked for heat once a day and bred

with non-frozen semen via artificial insemination by the farm staff Gilts were bred two

times (18 to 24 hours apart) after the first detection of estms and re-checked for retum to

estras. Gilts were allowed to consume a gestation diet of 2 kg/d (Table 3.1). Gilts were

fed once a day and had free access to water throughout the entire study. Each ofthe gilts

was assigned to represent one of six slaughter groups. Six gifts were slaughtered on d 0

(prior to breeding) to obtain base-line information about the uteras. Six gilts were

slaughtered on d 45 (44 to 48), four gifts were slaughtered on d 60 (59 to 61), five gifts

were slaughtered on d 75 (75 to 76), three gilts were slaughtered on d 90 (90 to 92), five

gifts were slaughtered on d 102 (101 to 104), and four gilts were slaughtered on d 110

(107 to 112) (Table 3.2).

51

Diet Soybean meal was used as a major protein source and com was used as a

major energy source ofthe gestation diet. The gestation diet provided a daily allowance

of 89.2% DM, 12.2% CP, 0.56% lysine, 3.1 Mcal/kg ME, and 0.94% Ca (Table 3.1).

Slaughter. Gifts were transported to the Texas Tech Meat Laboratory (Lubbock,

TX) in the evening before slaughter, where they were withheld from feed. The gilts were

weighed and then slaughtered in the moming, according to the Texas Tech Meat

Laboratory Standard Operating and Procedures Protocol for the Slaughter of Swine.

Sample Collection. The entire reproductive tracts were collected during the

processing ofthe carcass. Weights ofthe entire reproductive tracts were taken

immediately after collection. The reproductive tracts were then placed on a table and the

uterine membranes were removed, allowing for both homs to be spread out their entire

lengths for measurement. The length of each hom was measured in centimeters, and the

homs were then assigned to be the short side (S) and the long side (L). Fetuses were

identified in each hom and assigned a location by number. Location number one was at

the cranial-most extremfties ofthe hom, while the last location was at the cervical-most

extremity. The fetuses along with the partial collection ofthe placentas were separated

from the uterine hom by cutting the placenta, which was translucent in color, at the base

ofthe amniotic sac, which had a smooth texture and red color to ft, and then again at the

base ofthe umbilicus. Fetuses were weighed as a whole and further dissected via a

medial incision to expose individual organs. The placenta, heart, liver, lung,

gastrointestinal tract (GIT), kidneys, and spleen were collected via blunt dissection. The

52

spleens were collected from the fetuses only after d 75 of gestation, as they were not

clearly identifiable before d 75. The weights of all fetal tissues, as weU as the fetal

carcasses, were recorded.

Statistical Analysis. A complete randomized design was used with a general linear

model procedure (Proc GLM) of SAS (SAS Inst. Inc., Cary, NC), to perform the

statistical analysis ofthe data. The sow was used as an experimental unit. The mean was

modeled with fetal location as one main effect and litter weight coefficient of variation

(CV) as the other main effect. Standard errors and least squares means were obtained

from this model. Regression procedures (PROC REG) of SAS was used to describe the

quantitative changes of each tissue as location in the uterine hom proceeded cranial to

cervical.

Results

The fetuses found at the most cervical locations 10 and greater, were omitted in

the data analysis, due to lack of significant collection size. Only five fetuses were

collected at location 10 and greater.

Fetal tissues. When the data were pooled regardless of day of gestation in the

statistical analysis; weights ofthe fettis, fetal carcass, GIT, hver, heart, lung, spleen, and

kidney decreased (P < 0.05, linear) as uterine location ofthe fetus proceeded cranial to

cervical (Figure 4.1). When the data were grouped by day of gestation and analyzed

statistically, there was no correlation between fetal weight and uterine location on d 45,

53

75, 90, and 110 of gestation (P > 0.05), whereas there was a linear relationship between

fetal weight and uterine location on d 60 and 102 of gestation showing that the fetuses at

the cranial exfremities to be proportionally larger (P < 0.05) than those at the cervical

exfremities (Figure 4.2).

On d 45 of gestation, the liver weight decreased (P < 0.05, quadratic) as uterine

location ofthe fetus proceeded cranial to cervical (Figure 4.3). The weights ofthe

kidney, heart, lung, and GIT were not correlated (P > 0.05) with uterine location ofthe

fetus.

On d 60 of gestation, the fetal GIT and lung weights decreased (P < 0.05,

quadratic) as uterine location ofthe fetus proceeded cranial to cervical (Figure 4.4). The

fetal liver weight decreased (P < 0.05, quadratic) as uterine location ofthe fetus

proceeded cranial to cervical (Figure 4.5). The heart weight decreased (P < 0.05,

quadratic) as uterine location ofthe fetus proceeded cranial to cervical (Figure 4.6). The

fetal lung weight (g) decreased (P < 0.05, quadratic) as the uterine location proceeded

cranial to cervical (Figure 4.7). The fetal kidney weight decreased (P < 0.05, linear) as

uterine location ofthe fetus proceeded cranial to cervical (Figure 4.8).

On d 75 of gestation, the fetal liver weight increased (P < 0.05, cubic) as uterine

location ofthe fetus proceeded cranial to cervical (Figure 4.9). The weights ofthe GIT,

liver, heart, kidney, lung, placenta, and spleen were not correlated (P > 0.05) with uterine

location ofthe fetus.

54

On d 90 of gestation, the weights ofthe GIT, liver, heart, kidney, lung, and spleen

were not correlated (P > 0.05) with uterine location ofthe fetus.

On d 102 of gestation, the fetal liver weight decreased (P < 0.05, cubic) as uterine

location ofthe fetus proceeded cranial to cervical (Figure 4.10). The fetal heart weight

decreased (P < 0.05, linear) as uterine location ofthe fetus proceeded cranial to cervical

(Figure 4.11). The weights ofthe fetal GIT, kidney, lung, and spleen were not correlated

(P > 0.05) with uterine location ofthe fetus.

On d 110 of gestation, the weights ofthe fetal liver, kidney, GIT, lung, and spleen

were not correlated (P > 0.05) with uterine location ofthe fetus. The fetal heart weight

had a tendency to increase (P < 0.07, quadratic) as uterine location ofthe fetus proceeded

cranial to cervical (Figure 2.12)

Weight variations among littermates. On d 45 of gestation, a smaller (P < 0.05)

variation in littermate weight was observed than on d 75 and 102 of gestation (Table 4.2).

There was no correlation (P > 0.05) between litter weight variation on d, 60, 90, and i 10

of gestation.

Discussion

Intra-uterine location may influence the fetal growth by limiting the nutrient

supply to certain fetuses (Allyson et a l , 2001). This study indicates that fetal uterine

location influenced fetal tissue growth on d 60 and 102 of gestation. On these days, total

fetal weight was proportionally greater at the cranial-most extremities ofthe uterine hom,

55

implying that the cranial-most exfremities on these days receive more maternal nutrients.

These data suggest that tiie sow has a limited ability to supply those fetuses at the

cervical-most exfremities ofthe uterine hom. It is known that there are periods during

gestation tiiat the matemal requfrements for certain mineral and vitamins fluctuate

(Mahan and Vallet, 1997). These data suggest that on d 60 and 102 of gestation, the sow

is going through a period of increased nutrient demand. This fiirther suggests that a

fluctuation in matemal nutrient need occurs at or around d 60, which is supported by the

fmduig that all vital fetal organs, GIT, liver, heart, lung, and kidney weights, were found

to decrease as uterine location proceeded cranial to cervical on d 60.

Variations in piglet birth weights within a litter, often lead to an increase in nmt

mortality. This increased mortality is largely due to the increased competition with the

heavier littermates (Wise et ah, 1997). Several factors can control within-Iitter variation,

previous data indicate that matemal genetics is one such factor that is correlated with

litter weight variation (Damgaard et al., 2003). Matemal nutrition may be another factor

which influences within-Iitter weight variation. The data in this study indicate that d 75

and 90 of gestation had an increased variation in littermate weights, indicating that

increased competition for nutrients may be influenced at these days. This further

supports that a nutrient flucttiation is occurring at or after d 60 of gestation and that the

matemal nutrient supply may be limfted to supply all ofthe fetuses adequately. Litter

weight variation among littermates is a determining factor to piglet survival (Wise et al .

56

1997). A decrease in within-Iitter weight variation may promote for a more uniform litter

at birtft.

Results of this study suggest that the matemal nutrient requirements fluctuate

during gestation. An inability to adequately supply the developing fetuses may cause

some ofthe fetuses to experience periods of under-nutrition, and thus growth stunting.

These findings indicate that fetal growth may be affected by matemal nutrient supply

from d 60 of gestation.

Implications

This study indicates that the sow has a decreased ability to supply enough

nutrients to all the fetuses, beginning on d 60 of gestation. These resufts could be used to

implement new feeding strategies for the gestating sow based on a two-phase feeding

system, before d 60 and after d 60, to better allow all the fetuses to receive adequate

nutrients for optimal growth.

57

Table 4.1. Litter weight variation within day of gestation

Day of gestation

45 60 75 90 102 110 SEM'

CV 9.14*' 11.68*" 17.87' 16.50*" 17.74' 13.43'" 4.67

'Pooled standard error ofthe mean. *" Within a row, means that do not have a common superscript letter differ (P < 0.05).

58

680 -1

..660-S 640 -•S 620 -t 600 -I 580 -!« 560 -

520 -500 -

-t

3 4 5

Fetal uterine location

Figure 4.1 The weights ofthe whole fetus (g) decreased (P < 0.05, linear) as fetal location proceeded cranial to cervical, when data were pooled in the analysis (y = -7.54 x + 646.71, r̂ = 0.60 where x = fetal location and y = fetal tissue wt, g).

59

+ ^ 43 _SJD

*S

3

.a • « -̂

180

160 : .

140 -•

120 ^-

100

80 H

60

40

20 ^

0

1 4 5

Fetal location

Figure 4.2 The weights ofthe whole fetus (g) on d 60 of gestation decreased (P < 0.05, linear) as fetal location proceeded cranial to cervical, when day of gestation was not considered in the analysis (y = -5.64 x + 149.45, ̂ = 0.77 where x = fetal location and y = fetal tissue wt, g).

60

1

2

I

3 4

1

5

1 1

6 7

Fetal location

1

8

1

9

1

10

1

11

1

12

Figure 4.3 Fetal liver weights (g) by different uterine locations on d 45 of gestation. Fetal liver weight decreased (P < 0.05, quadratic) as fetal location proceeded cranial to cervical (y = - 0.0155 x^ + 0.1473 x + 1.9552, ? = 0.71 where x = fetal location and y = fetal liver wt, g).

61

Fetal location

Figure 4.4 Fetal GIT weights (g) by different uterine location on d 60 of gestation. Fetal GIT weight decreased (P < 0.05, quadratic) as fetal location proceeded cranial to cervical (y = -0.0131 x^ - 0.0397 x + 4.2661, / = 0.82 where x = fetal location and y = fetal GIT wt, g).

62

&£

<u

iZ -

10 '

8 '

6 -

4 -

2 -

0 -

•""•—-.,__ T

r~~~-f-i

1 1 1 1

F-_L__^

1 1

I

1 1

i

1

4 5 6 7

Fetal location

9 10 11

Figure 4.5 Fetal liver weights (g) by different uterine location on d 60 of gestation. Fetal liver weight decreased (P < 0.05, quadratic) as fetal location proceeded cranial to cervical (y = 0.0354 x^ wt, g).

-̂ 0.8579 X + 10.299, r̂ = 0.83, where x = fetal location and y = fetal liver

63

6 7

Fetal location

11

Figure 4.6 Fetal heart weights (g) by different uterine locations on d 60 of gestation. Fetal heart weight decreased (P < 0.05, quadratic) as fetal location proceeded cranial to cervical (y = -0.0049 x^ + 0.016 x + 1.053, ^ = 0.82, where x = fetal location and y = fetal heart wt, g).

64

5 6 7

Fetal location

10 11

Figure 4.7 Fetal lung weights (g) by different uterine location on d 60 of gestation. Fetal lung weight decreased (P < 0.05, quadratic) as fetal location proceeded cranial to cervical (y = - 0.0161 x^ - 0.1106 x + 5.7218, r̂ = 0.77, where x = fetal location and y = fetal lung wt, g).

65

4.0 n

3.5

3.0 M

& 2.5

-g 2.0

4S 1.5 ^

1.0

0.5 -

0.0

1

"T 1 1 r

5 6 7

Fetal location

1 1

10 11

Figure 4.8 Fetal kidney weights (g) by different intrauterine locations on d 60 of gestation. Fetal kidney weight decreased (P < 0.05, linear) as fetal location proceeded cranial to cervical (y = -0.1382 x + 3.0655, r^= 0.89, where x = fetal location and y = fetal kidney wt, g).

66

25

20

b£

u

« 10 ii

2 4 5 6

Fetal location

7

Figure 4.9 Fetal liver weights (g) by different uterine location on d 75 of gestation. Fetal liver weight increased (P < 0.05, cubic) as fetal location proceeded cranial to cervical (y = 0.0924 x^- 1.1732 x^ + 4.2225 x + 10.131, r̂ = 0.83, where x = fetal location and y = fetal liver wt, g).

67

40 n

4 5 6

Fetal location

Figure 4.10 Fetal liver weights (g) by different uterine location on d 102 of gestation. Fetal liver weight decreased (P < 0.05, cubic) as fetal location proceeded cranial to cervical (y = -0.0964 x^ + 1.484 x^ - 7.641 x + 40.963, r̂ = 0.62, where x = fetal location and y = fetal liver wt, g).

68

12

10 -

M

.S

V

^

2 -

4 5 6

Fetal location

Figure 4.11 Fetal heart weights (g) by different uterine location on d 102 of gestation. Fetal heart weight decreased (P < 0.05, linear) as fetal location proceeded cranial to cervical (y = -0.26x + 10.011, r̂ = 0.63, where x = fetal location and y = fetal heart wt,

g)-

69

ii

50 -|

45 -

40 '-

35

30 -

25 -

20

15

10

5

0

1 I

2 6 1 4 5

Fetal location

Figure 4.12 Fetal heart weights (g) by different uterine location on d 110 of gestation. Fetal heart weight showed a tendency (P < 0.07, quadratic) to increase as fetal location proceeded cranial to cervical (y = 0.3667 x^ - 2.2857 x + 37.261, ? = 0.49, where x = fetal location and y = fetal heart wt, g).

70

Literature Cited

Allyson, K. C , N. Stickland, and C. Stickland. (2001). Porcine satellite ceUs from large and small siblings respond differently to in vitro conditions. Basic Applied Myology, 11,45-49.

Bauer, M. K., J. E. Harding, N. S. Bassett, B. H. Breier, M. H. Oliver, B. H. Gallaher, P C. Evans, S. M. Woodall, and P. D. Gluckman. (1998). Fetal growth and placental function. Journal of Molecular Cell Endomology, 140(1-2),115-120.

Damgaard, L. H., L. Rydhmer, P. Lovendahl, and K. Grandison. (2003). Genetic parameters for within-Iitter variation during suckling. Journal of Animal Science, 81,604-610.

Johnson, R. K., M. K. Nielsen, and D. S. Casey. (1999). Responses in ovulation rate, embryonal survival, and litter fraits in swine to 14 generations of selection to increase litter size. Journal of Animal Science, 11, 541-557.

Mahan, D. C , and J. L. VaUet. (1997). Vitamin and mineral transfer during fetal development and early postnatal period. Journal of Animal Science, 75, 2731 -2738.

Merck Vetermary Manual. (1998). Merck Veterinary Manual S"' ed., (pp. 1485-1495). Merck & CO., Inc, National Publishing Inc., Philadelphia, PN.

Reece, W. O. (1997). Physiology of Domestic Animals, (p. 376). WiUiams and WUkins. ' Baltimore, MD. USA.

Wise, T., A. J. Roberts, and R. K. Christenson. 1997. Relationships of light and heavy fetuses to uterine position, placental weight, gestational age, and fetal cholesterol concentrations. Journal of Animal Science, 75, 2197-2207.

VaUet, J. L., K. A. Leymaster, and R. K. Christenson. 2002. The influence of uterine ' fimction on embryonic fetal survival. Journal of Animal Science, 80 (E. Suppl. 2),

E115-E125.

71

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