effects of varying particle size of forage on digestion and chewing behavior of dairy heifers

Effects of Varying Particle Size of Forage on Digestion and Chewing Behavior of Dairy Heifers 1

E. H. JASTER and M. R. M U R P H Y Department of Dairy Science

University of Illinois Urbana 61801

ABSTRACT

Eighteen Holstein heifers were fed long and chopped coarse and fine alfalfa hay ad libitum to evaluate effects of physical form on digestion and chemical composition of feed and fecal particles and to examine the applicability of a sinusoidal model to chewing behavior. Recordings of jaw movement were divided into 1-h segments for analysis. Least square mean size of fecal particles from coarse and finely chopped diets were 290 and 297 /lm as compared to 227 /lm on long hay. Intakes of dry matter were greater and digestibilities lower for chopped as compared to long hay. Crude protein content of separated feed and fecal particles increased as particle size decreased. Neutral and acid detergent fiber concentrations decreased in feed and feces with decreasing particle size. Lignin content of feed particles decreased as particle size decreased, whereas for fecal particles lignin as a percent of cell wall followed a "U" shaped pattern of declining then increasing as size decreased. Patterns were sinusoidal for eating and ruminating long and chopped hays and total chewing (eating and ruminating) of long hay. Our results suggest a gradual effect on chemical degradation and physical detrition of digesta particles and chewing behavior as forage particle size decreased.

I N T R O D U C T I O N

The physical breakdown of forages is an integral part of ruminant digestion. It serves to

Received June 4, 1982. 1Supported by Illinois Agricultural Experiment

Station, Hatch 35-356 and 35-360.

increase surface area av~ailable to rumen micro- bes and enhance both digesta passage and feed intake. These effects and decreased digestibility generally are observed when forage particle size is reduced prior to feeding by chopping or grinding (2, 4, 5, 17). Specific results depend heavily on the size distribution of feed particles (24). There is little quantitative informa- tion describing effects of physical form of forage on feed and fecal particle size and chemical composition (16, 18, 23).

Chewing during eating and rumination is an important component of reduction of particle size. Dilution rate and buffering capacity of rumen fluid also are influenced by chewing via its effect on salivation (3). A basic circadian rhythm in which rumination peaks during the early morning hours has been observed fre- quently (10). Many time plots of sheep rumination can be described quantitatively as sinusoids (13). An understanding of particle size reduction, digestion, and passage is needed, especially with current trends towards optimizing forage utilization.

Our objectives were to evaluate effects of particle size of alfalfa hay on intake, digestibility, and chemical composition of feed and fecal particles (Trial 1) and to examine the applicability of a sinusoidal model to eating, ruminating, and total chewing (eating and ruminating) behavior of cattle (Trial 2).

M A T E R I A L S A N D METHODS

Trial 1

Eighteen Holstein heifers averaging 340 kg were assigned randomly to three groups and fed long hay for a 7-day preexperimental period. During the experiment animals in each group were fed a sequence of three diets for three successive 21-day periods in a replicated 3 × 3 Latin square with three animals per group. The diets consisted of alfalfa hay in three physical

1983 J Dairy Sei. 66:802-810 802

PARTICLE SIZE EFFECTS ON DIGESTION AND CHEWING 803

forms: long and coarsely or finely chopped. Hay was chopped prior to feeding by a field harvester (New Idea Unisystem, Davenport, IA) fixed with or without a 10.2-cm screen for fine and coarsely chopped hay. Heifers were housed in stanchions and fed hay ad libitum (10% orts) once daily (1200 h). Feed intake was recorded daily. Animals were provided free access to water and normally allowed to exercise for 60 min daily in an outside lot beginning at 1100 h.

Feed and Fecal Analyses. Feed was collected weekly during the experiment, and fecal grab samples were taken during the final 3 days of each period at 0700 h. Feed and feces from each animal were composited separately, oven- dried at 55°C for 3 days, ground through a Wiley Mill (2 mm screen), and analyzed for dry matter, neutral detergent fiber (NDF), acid detergent fiber (ADF), and 72% sulfuric acid detergent lignin (ADL) by methods of Goering and Van Soest (8). Concentrations of cellulose and hemicellulose were estimated by subtrac- tion of ADL from ADF and ADF from NDF. Crude protein content was calculated as Kjel- dahl N x 6.25. The acid-insoluble ash (A1A) marker method was used for determination of nutrient digestibility coefficients (22).

Feed Particle Size and Chemical Composi- tion. Coarse and finely chopped alfalfa hay particle size distributions were estimated by a dry sieving technique (25). For each feed, fractions were collected that remained on screens of 150, 4 1 7 , 8 5 0 , 1180, 1700, and 2360 ktm. Separated hay particles were analyzed for fiber and crude protein composit ion as described. The 1180, 1700, and 2360-ktm alfalfa hay particles were ground through a Wiley Mill (2 mm screen) prior to determination of fiber and crude protein.

Fecal Particle Size and Cbemical Composi- tion. Size distributions of refrigerated feces were analyzed by wet sieving. A subsample of approximately 50 g was flushed through a nest of six sieves (sieve opening sizes of 75, 150, 300, 4 1 7 , 6 0 0 , and 8 5 0 / l m ) with water. Mate- rial passing through the smallest sieve was not recovered ; therefore, the percentage of subsam- pie 55°C dry matter retained on each sieve was calculated from results of a dry matter determination on an unsieved subsample. Fiber and crude protein composit ion of separated fecal particles were determined as described. Dried fecal size fractions were pooled within period

and diet to obtain sufficient material for chemical analysis. The relationship between probit (normal equivalent deviates coded by the addi- tion of 5.0) transformed (20) cumulative percent of the sample dry matter greater than a particular sieve size and log10 sieve size for fecal material had a significant quadratic component. Mean particle size was estimated by solving quadratic regressions at a probit of 5.

Statistical analyses were by a general linear model procedure (SAS Institute Inc., Raleigh, NC).

Trial 2

Chewing activity was monitored during the last 12 days of each of the periods in Trial 1. All 18 heifers had their jaw movements recorded for 48 h once during the experiment, i.e., in each period six animals (two per diet) were studied. The design was randomized com- pletely for animals and diets. This activity also was observed visually every 5 min for 24 h on all 18 animals.

Jaw movements were transmitted to a water filled rubber balloon attached to halter chin straps. Vibrations were conducted through water filled polyethylene tubing to either a Beckman type 802 or Statham type P 23 AA transducer. Electrical impulses were amplified by an Offner type R 8 channel Dynograph and recorded on a Honeywell Electronik 194 lab recorder with a chart speed of 12.7 mm/min. Time spent eating and ruminating and number of boluses ruminated were taken from records divided in 1-h segments. Chewing activity for each interval was fraction of time spent eating or ruminating.

Data were analyzed with the cosinor model of Halberg et at. (11), which used the equation F = C o + C cos (c0t + ~), where fraction of time spent eating, ruminating, or chewing was a function of Co, the fi t ted mean; C, amplitude; co, the (fixed) angular frequency; t, time; ~, phase. An underlying 24-h rhythm was assumed based on data where sheep were fed hourly or once daily (13). This allowed co to be fixed at unity provided time was in radians (27r/d).

Least square estimates of Co, C, and ~ were by a derivative-free nonlinear regression technique (15). Analysis of variance of ruminated bolus data was by a general linear model procedure (SAS Insti tute Inc., Raleigh, NC).

Journal of Dairy Science Vol. 66, No. 4, 1983

804 JASTER AND MURPHY

TABLE 1. Average chemical composition of the alfalfa hay diets.

Long Nutrient hay

Forage

Coarse Fine chop chop

Dry matter, % 89.5 90.2 89.8

(% Dry matter)

Crude protein 16,3 15.7 15.9 Neutral detergent fiber (NDF) 63.1 63.0 62.1 Acid detergent fiber (ADF) 38.6 45.4 43.3 Acid detergent lignin (ADL) 9.8 10.9 10.4 Cellulose a 28.8 34.5 32.9 Hemicellulose b 17.5 17.6 18.8

aADF minus ADL. bNDF minus ADF.

RESULTS A N D DISCUSSION

Trial 1

Mean chemica] c o m p o s i t i o n s for long and c h o p p e d alfalfa hay diets are in Table 1.

C h o p p e d ha ys had h igher A D F and A D L bu t lower c rude p ro t e in c o n c e n t r a t i o n s t h a n long hay . This could be f r o m loss dur ing c h o p p i n g o f f ine mater ia l which had relat ively h igher c rude

TABLE 2. Least square mean nutrient intake and digestion coefficients as affected by forage particle size.

Forage Orthogonal Long Coarse Fine c°mparis°na hay chop chop SE A B

Intake (ad libitum), kg/day DM c 8.0 8.4 8.5 .2 P<.06 NS b NDF c 4.5 5.3 5.3 .1 P<.OO01 NS ADF c 3.10 3.83 3.69 .08 P<.O001 NS ADL c .78 .90 .88 .02 P<.O002 NS Hemicellulose 1.45 1.48 1.60 .03 P<.03 P<.01 Cellulose 2.38 2.98 2.84 .06 P<.O001 NS Crude protein 1.33 1.35 1.36 .04 NS NS

Digestibility, % DM 62.6 61.3 56.3 1.3 P<.03 P<.01 NDF 59.3 58.6 57.6 .4 P<.O1 P<.07 ADF 54.1 55.1 52.8 .4 NS P<.O001 ADL 26.0 25.8 24.6 1.1 NS NS Hemicellulose 70.5 67.9 68.8 .9 P<.06 NS Cellulose 62.6 63.4 61.3 .4 NS P<.O01 Crude protein 73.3 72.1 71.4 .5 P<.O 1 NS

a Comparison A, long versus chopped hay; B, coarse versus fine chopped hay.

bNot significant, P>.10.

CDM = Dry matter, NDF = neutral detergent fiber, ADF = acid detergent fiber, and ADL = acid detergent lignin.



98 --

95

90

~" so 0 70

U 6o 5o

n ~o ) ,

B

m

0 I I 1 1 I I 50 IO0 2 0 0 4 0 0 8 0 0 1600 3 2 0 0

SIEVE SIZE (~n? )

Figure 1. Feed and fecal particle size distribution. Coarse (o) and finely (i) chopped hay, as fed; and fecal dry matter from animals fed long (Lx), coarse (~), and finely (u) chopped hay on sieves with different size openings.

protein and lower concentrations of ADF and ADL.

Dry matter and fiber intake were greater when chopped hays were fed (Table 2). In- creased intakes of NDF, ADF, ADL, cellulose, and hemicellulose resulted from increased intake of DM (P<.06). Heifers consuming chopped hay had decreased digestibilities of DM, NDF, hemicellulose, and crude protein as compared to long hay. This trend of decreasing fiber digestibility was also apparent as particle size decreased in chopped hays. Reducing particle size by chopping and grinding increases both DM intake and rate of food passage through the rumen while decreasing digestibility (2, 4, 5, 17).

Distributions of feed and fecal particle sizes are in Figure 1. Least square mean particle sizes of coarse and finely chopped hays were 2160 (SE 94) and 1440 (100)/~m, Least square mean fecal particle sizes on coarse and finely chopped diets were 290 (9) and 297 (9) #m as compared to 227 (9) #m on long hay (P<.0001). Other studies also have indicated that fecal particle size increases with intake of forage or reduction in forage particle size (19, 23). The increased fecal particle size probably indicates faster rate

of digesta passage on chopped diets (26). Crude protein concentrations in separated

feed and fecal particles are in Figure 2. Crude protein content of feed increased as particle size decreased. Similarly, fecal crude protein in-

I 0 - -

8 - -

4

o l ] t i I I I 1(30 500 900 13(30 1700 2 1 0 0 2500

STEVE SiZE ~a'/)

Figure 2. Feed and fecal crude protein content of particles on sieves with different size openings. Coarse (o) and finely (i) chopped hay. Feces from animals fed long (n), coarse (o), and finely (~) chopped hay.

90 --

80

~o 55~ ~---~ z

6 C - -

50

4 0 - -

o ' ' l I i I I I I tOO 500 900 1300 ~700 2tO0 2500 SIEVE SIZE (~m)

Figure 3. Feed and fecal neutral detergent fiber (NDF) content of particles on sieves with-different size openings. Coarse (o) and finely (i) chopped hay. Feces from animals fed long (~), coarse (o), and finely (~) chopped hay.



8 l

22r 2 5 p f 2 o l i 1 I I I I

I00 500 900 GO0 1700 2100 2500 SIEVE SIZE (~rrl)

Figure 4. Feed and fecal acid detergent fiber (ADF) content of particles on sieves with different size openings. Coarse (o) and finely (m) chopped hay. Feces from animals fed long (z~), coarse (o), and finely (u) chopped hay.

l ions decreased as particle size decreased in separated feed and fecal material (Figures 3 and 4). A similar decrease in hemicel lulose and cellulose concent ra t ions in digesta particles less than 250 /lm was observed by Reid et al. (16). Chemical composi t ions of fecal particles of different size apparent ly cont inued to ref lect those of the feed. It was recognized that the detergent system (8) may be inf luenced by particle size of sample. Heller et al. (12) repor ted that red wheat bran ground through a 60-mesh screen had significantly lower contents of NDF and hemicel lulose than the same material ground through a 20-mesh screen. Crude protein analyses should no t be affected by sample particle size. Al though feed and fecal crude protein contents versus particle size dis- t r ibut ions are inverted f rom those of the fiber analyses, they are of similar shape; therefore , possible errors in t roduced by fiber analyses of particle size fract ions are considered small.

30 ~ 40 - -

58 25 u

56

20 34

~n 32 ~ 15 ..A

i ~ 30

d 28 1o m li z 26

5 [ I t ] [ I I I I I I - z +00 500 900 1500 I?00 2100 2500 Z 24

SIEVE SIZE ( ~ ) ~ 22 - -

Figure 5. Feed and fecal acid detergent lignin z ~ (ADL) content of particles on sieves with different ~ 20 size openings. Coarse (o) and finely (m) chopped hay. ~ 18 Feces from animals fed long (Lx), coarse (o), and finely ~- (n) chopped hay. 16

creased with decreasing particle size. Leaf and fine stem fragments probably cont r ibuted to higher crude prote in con ten t of smaller feed particles. At tached bacteria may have con- t r ibuted a higher p ropor t ion of crude prote in to smaller fecal particles, which have a relatively large surface area.

Neutral and acid detergent f iber concentra-

14

12

I¢

0

w

_-\ °i°/° _ ,oJ m

I I I I 1 200 4 0 0 600 800 I000

SIEVE SIZE (,urn) Figure 6. Fecal acid detergent llgnin (ADL) as a

percent of cell wall (neutral detergent fiber) on sieves with different size openings; o, average for heifers fed long, coarse, or finely chopped alfalfa hay; *, data of Van Soest (11) for animals fed alfalfa hay; ~, data of Smith (8) for sheep fed orchard grass pellets.



1.0

0 c

- - • o o o °

• o o o °

I I I I .srr f.orr r.STr z.orr

0600 12o0 18oo 2400 TIME (rcld~ arts )

Figure 7. Diurnal pattern of time spent ruminating long hay, e; least squares fit of cosinor model, - - .

Lignin con ten t of feed particles decreased with decreasing particle size (Figure 5). No pat tern was apparent in lignin conten t of fecal particles of different sizes. Expressing lignin con ten t as a percent of cell wall (NDF) al lowed our data on fecal particle compos i t ion to be compared with data f rom the l i terature (Figure 6). A " U " shaped pat tern of decreasing then increasing lignin con ten t as a percent of cell

wall was observed as fecal part icle size decreased. This pat tern is similar to that repor ted by Smith (18) for feces f rom sheep fed orchard grass pellets but differs f rom prel iminary results of Van Soest (23) with animals fed alfalfa. Small fecal particles should have higher lignin conten t as a percent of cell wall as they have been digested most extensively leaving only re- f ractory material . It is also possible that larger fecal particles represent a por t ion of feed material that , because of originally high lignin content as a percent of cell wall, underwent pri- marily physical degradat ion necessary for passage.

Our results suggest there is a gradual effect on digestion as forage particle size decreases. They also underscore that both chemical degradat ion and physical detr i t ion are impor tan t componen t s of ruminant digestion. Fur ther progress in manipula t ing this complex process wilt require a more detailed unders tanding of the concer ted act ion of chemical and physical at tack in making nutr ients available to the animal.

Trial 2

Cosinor analysis results for chewing pat tern data f rom chart recordings are in Table 3.

TABLE 3. Cosinor analysis of chewing pattern data.

Activity diet Mean (Co)

Residual sum of

Amplitude (C) Phase (4) squares

SD a X SD X SD Ruminating

Long hay .33 .02 - .14 Coarse chop .33 .02 - .14 Fine chop .35 .02 - .14

Eating Long hay .37 .03 .24 Coarse chop .36 ,03 .15 Fine chop ,34 .03 .17

Chewing Long hay .70 .02 .12 Coarse chop .69 .02 .02 Fine chop .69 ,02 ,04

.03 2.8 .2 .21

.03 2.9 .2 .26

.03 3.1 ,2 .21

.04 2.5 .2 .47

.05 2.7 .3 .55

.04 3.0 .3 .47

.02 2.2 .2 .12

.03 1.8 1.3 .19

.02 2.6 .6 .13

aEstimated standard deviation.


8 0 8 JASTER AND MURPHY

1.0

a: .8 o o

-~ .6

LLI

~-- ~4

P-- .2

o I I I I o .5~r ~.orr ~.srr zo~r

0600 1200 1800 2 4 0 0 TI ME(r°d~ ons )

Figure 8. Diurnal pat tern of t ime spent eating long hay, • ; least squares fit of cosinor model, - - .

1.0 m

z .z

I I 1 I 0 .STf LO'lr 1.5t7" 2 D ~

0 6 0 0 F200 1800 2 4 0 0

TIME (rod~ °ns )

Figure 9. Diurnal pat tern of t ime spent chewing long hay, e; least squares fit of cosinor model, - - .

R h y t h m s o f r u m i n a t i o n w e r e a p p a r e n t ; i.e., c o s i n e a m p l i t u d e s w e r e n o t n e a r ze ro ( F i g u r e 7 a n d T a b l e 3). A m p l i t u d e s w e r e s imi l a r a c r o s s d i e t s to t h o s e f o r o n c e da i ly a n d h o u r l y f e d

• s h e e p (13) . P e a r c e ( 1 4 ) r e p o r t e d s h e e p fed ad l i b i t u m t e n d e d to lose d e f i n i t i o n in d i u r n a l

r u m i n a t i o n p a t t e r n s ; h o w e v e r , th i s was n o t con- f i r m e d fo r c a t t l e in o u r s t u d y . R h y t h m s fo r e a t i n g b e h a v i o r we re also e v i d e n t a l t h o u g h m o r e va r i ab l e as i n d i c a t e d b y h i g h e r r e s idua l s u m s o f s q u a r e s t h a n t h o s e fo r r u m i n a t i o n c u r v e s ( F i g u r e 8 a n d T a b l e 3). A r h y t h m fo r

TABLE 4. Chewing activity and related measurements .

Measure Long hay Coarse chop Fine chop

SD a X SD X, SD Total t ime spent (h/day)

Rumina t ing 8.0 .5 8.0 .5 8.5 .5 Eating 8.9 .7 8.6 .8 8.1 .7 Chewing 16.9 .4 16.6 .4 16.6 .4

Peak activity t ime (h:min) Rumina t ing 1 : 12 : 49 : 57 : 52 : 06 : 48 Eating 14:19 :41 13 : 26 1 : 10 12 : 32 1:04 Chewing 15:32 :05 17:16 5:02 14:09 2:15

Rumina ted bolus data Boluses/min ruminat ionb 1.27 .04 1.18 .04 1.15 sec/bolus 47 51 52 Boluses/day 606 566 584

Ratio (scaled to long hay) Boluses/min ruminat ion 1.000 .929 .906 Time spent eating 1.000 .960 .908

.04

aEst imated s tandard deviation.

bLeast squares means and standard errors. Orthogonal comparisons: Long hay > chopped hays; P< .10 ; and coarse chop > fine chop, P> .10 .


P A R T I C L E S I Z E E F F E C T S O N D I G E S T I O N A N D C H E W I N G 8 0 9

1.6O

1.50

5 L4C

~30

I O 0

2:~DO

. / allR

I I I I 0300 0700 IlO0 1500

TIME (h)

45

g

55

60

I I 1900 2500

Figure 10. Dirunal pattern of boluses per minute of rumination for long, A--A; coarse, o---o; and fine, m---m; chopped alfalfa hay. Arrow indicates time of feeding.

total chewing activity was suggested for cattle fed long hay (Figure 9 and Table 3); however, those fed chopped hays distributed their chewing evenly thoughout the day. Mean, Co, and phase, 4, of the fi t ted cosines were used to estimate total time spent and peak time for each activity, respectively (Table 4).

That chopped hays were large enough to stimulate rumination and dry matter intakes increased when they were fed may explain similar total times spent chewing across diets (Table 4). Comparable results were reported by Sudweeks et al. (21).

Progressively less t ime was spent eating as hay particle size decreased. Ingested feed pre- sumably is chewed during eating and mixed with saliva until an acceptable size and con- sistency for deglutition is reached. For cows fed hay or herbage a range of mean particle size of from 1244 to 1602/am was observed by Gill et al. (7) for boluses collected at the cardia. Our finely chopped diet, at 1440 ~tm, was within this range and would have required minimal added chewing before swallowing.

Peak rumination activity occurred between midnight and 0115 h. This was 3.5 h earlier than estimated for sheep (13) and may indicate species, photoperiod, or other effects on the rhythm. Eating activity peaked shortly after animals were offered feed even though they

were fed ad libitum (10% orts). They appar- ently were anticipating their next meal as con- siderable eating occurred prior to scheduled feeding time. Data in Table 4 also suggest that eating and ruminating activity peaked almost directly out of phase (12 h). This is probably a fortuitous result as other workers have not been able to affect peak rumination by changing feeding time (9, 27).

Fewer boluses were processed per minute of rumination as hay particle size decreased. A similar result was apparent in the data of Voskuil and Metz (24) for lactating cows fed either long or chopped hay. We also observed an increase in mean fecal particle size as hay particle size decreased (Figure 1). This may indicate a reduction in rumination effectiveness (i.e., its ability to cause physical degradation of digesta) as time spent ruminating was similar across diets. Chewing rate during rumination varied with diet (6) and feed intake (1); therefore, a conclusion about effectiveness of rumination must be considered tentative without data of chewing rate. When scaled to what was observed for long hay, boluses per minute of rumination and time spent eating were similar. Less time spent eating finer diets may have been compensated for by increased time spent ruminating each bolus.

Diurnal patterns of boluses per minute of rumination are in Figure 10. Measures for coarse and finely chopped hay fluctuate near their mean throughout the day. With long hay a dramatic decrease in boluses per minute of rumination occurred near feeding time. After feeding, an abrupt increase was observed in the number of boluses processed per minute of rumination before returning to baseline about 6 h after feeding. This large increase after feeding could reflect an a t tempt by the animal to use rumination for rapidly reducing the size of recently ingested long hay particles.

Data from 24-h visual observation of chewing activity also were subjected to cosinor analysis. Larger standard deviations were estimated for rhythm components which indicated more data of this type would be required for accurate assessment of chewing patterns.

In summary, the sinusoidal model was ap- plicable to rhythms of chewing behavior of eating and rumination in cattle fed hay ad libitum. As hay particle size decreased, progressive changes in chewing occurred. It remains to be



de t e rmined whe the r this t echnique can enhance reso lu t ion of dietary differences, the reby enabling chewing r h y t h m s to be exp lo i t ed for manipula t ing rumen fe rmen ta t ion .

A C K N O W L E D G M ENTS

The authors apprecia ted statistical advice of R. D. Shanks and the assistance of D. F. Bell, B. A. Crooker , D. A. Grenawal t , R. R. Grum- mer, H. R. Newman, Jr. , J. L. Vicini, H. D. Whets tone , and especially M. J. Knight and N. S. Braun in various aspects o f this s tudy.

REFERENCES

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3 Bartley, E. E. 1976. Bovine saliva: production and function. Page 61 in Buffers in ruminant physiology and metabolism. M. S. Weinberg and A. L. Sheffner, ed. Church and Dwight Co., Inc., Pisca- taway, NJ.

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9 Gordon, J .G. 1958. The effect of time of feeding upon rumination. J. Agric. Sci. 51:83.

10 Gordon, J. C., and I. K. McAllister. 1970. The circadian rhythm of rumination. J. Agric. Sci. 74: 291.

11 Halberg, F., Y. L. Tong, and E. A. Johnson. 1967. Circadian system phase--an aspect of temporal morphology; procedures and illustrative examples. Page 20 in The cellular aspects of biorhythms. H. yon Mayersback, ed. Springer-Verlag Inc., New

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effects of varying particle size of forage on digestion and chewing behavior of dairy heifers

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