Br. vet..]. (1993). 149, 595

REPRODUCTIVE PATTERNS OF THE YAK. III. LEVELS OF PROGESTERONE AND OESTRADIOL-17fl

DURING PREGNANCY AND THE PERIPARTURIENT PERIOD

S.J. YU, Y. M. HUANG and B. X. CHEN

Depmlment of Veterina)y Medicine, Gansu Agricultural University, Lanzhou, Gansu, Peoples Republic of China

SUMMARY

Changes in plasma progesterone and oestradiol-17fl in yaks during preg- nancy and the periparturient period of yaks and ill milk during the first month of pregnancy were analysed. The profiles of progesterone were similar for pregnant and non-pregnant yaks within 14 days following oestrus (P>0.05), but the concentration was significantly higher on day 19 (P<0.05) and in pregnant yaks tended to increase gradually thereafter. Tile plasma progesterone decreased rapidly on day 120 (P<0.05), then increased to reach its maximum of 15.5 (SD 3.74) ng ml -~ on day 210; declined again 20 days before parturition and resumed the same levels at parturition as during mating (P>0.05). The oestradiol-17fl levels in plasma and milk increased gradually from day 23 after conception, decreased abruptly on day 60 (P<0.05), then increased to reach their maximum at parturition of 551.4 (SD 70.86) pg ml -l. The oestradiol decreased again after parturition to the same level as during mating (P>0.05).

INTRODUCTION

Progesterone and oestradiol-17fl in both peripheral blood and milk during various reproductive periods have been determined for domestic animals. How- ever, information concerning the levels of these hormones in the yak is scarce. The authors have already assayed these two steroid hormone levels just before the breeding season, during normal and short oestrus cycles (Yu et al., 1993). The scope of the present project was to investigate the changes in progesterone and oestradiol-1713 levels during pregnancy and the periparturient period.

0007/1935/93/060595-08/$08.00/0 © 1993 Bailli6re Tindall

596 BRITISH VETERINARY JOURNAL, 149, 6

MATERIALS A N D M E T H O D S

Animals Twelve multiparous yak cows, 5-11 years of age, and two yak bulls, 7 and 8 years

of age, were kept on high mountain grassland at an elevation of 2500-3000 m above sea-level in Tianzhu Autonomous County of Gansu. The range was good and the experimental yaks grazed freely all year round. All were given supplemen- tary feed in the evening from February to April when the grass was covered by deep snow, and were in good condition. Their growth and reproductive perform- ance were normal, and there were no apparent genital abnormalities. The time of mating and calving was recorded from careful observations.

Samp//ng Blood and milk samples were collected from 12 yak cows in the first month of

pregnancy. Blood was obtained daily for the first 20 days and every 2 days for the following 10 days; milk was collected every day. Thereafter, only 8 of the 12 yaks were blood-sampled until the end of the experiment, the samples being collected once a month following mating until the 7th month of gestation. Using an esti- mated gestation period of 254 days, blood was collected on days 20, 15, 10, 5, 2, and 1 before parturition; at the beginning of parturition; 3, 7 and 15 hours, and 1, 3, 5, 10, 15 and 20 days after parturition. But for those animals whose duration of pregnancy was longer or shorter than 254 days, samples were collected once daily when distinct signs of parturition appeared (about 3 days before parturition). In the calculations, the progesterone and oestradiol-17fl values of all these animals were adjusted to a 254-day duration.

Collection and storage of both milk and blood samples were the same as described previously (Yu et al., 1993).

Pregnancy diagnosis Pregnancy was diagnosed by rectal palpation one month after mating.

Hormone assay and statistical analysis The assay of progesterone and oestradiol-17fl in plasma and milk and the stat-

istical analysis system were as described by Yu et al., 1993.

RESULTS

Levels of progesterone in plasma and milk During the first month of pregnancy. The combined data for 12 cows are shown in

Fig. 1. The progesterone values were 0.25 (sD 0.12) ng ml -~ in the plasma and 0.49 (SD 0.27) ng ml -~ in the milk on the day of mating (day 0) and for the next 2 days; they then rose gradually to day 5 when levels in the milk rose markedly (P<0.05). The plasma and milk progesterone concentrations reached 7.06 (sD 1.75) and 36.85 (sD 10.84) ng ml -~ on day 14 after which there was a sharp drop to 4.29 (sD 0.09) and 22.01 (sD 9.43) ng ml -I on day 15 (P<0.05). The values increased again

REPRODUCTIVE PATTERNS OF THE YAK III. 597

60

50

40

7~ 30

20

10:

8 0

~: 6

0

Mating

~ 1 1 I I I I I I I [ I 0 2 4 6 8 i0 12 14 16 18 20 22 24 26 28 3'0 t

Time (days)

Fig. 1. Concentrations of plasma and milk progesterone during the first month of pregnancy (ru~12). Milk progesterone (©);plasma progesterone (0) .

20

18

16

c~

I0

Mating

0 30 60 90 120 150 180" 210" 240" 245 250 252 254 L | ~ 0 1 5 I0 15 20

Parturition Time (days)

Fig. 2. Concentrations of plasma progesterone during the whole pregnancy and periparturition period (n=8).

598 BRITISH VETERINARY JOURNAL, 149, 6

gradually and were as high as 7.27 (SD 2.12) ng ml -I in the plasma and 34.48 (st) 14.54) ng m1-1 in the milk on day 30.

During the whole of pregnancy and the peripartu~@nt period. Th e plasma progester- one level was 0.3 (SD 0.15) ng ml -~ on the day of mat ing in eight of the above 12 females (Fig. 2). It increased gradually to 11.17 (sD 2.31) ng ml -~ on day 60, then dec l ined to reach a much lower value by day 120 [7.93 (SD 1.81) ng ml-l], (P< 0.05). Values then increased again to reach a m ax im u m of 15.45 (SD 3.74) ng ml -I on day 210 after which there was an abrup t decl ine on day 239 (P<0.01). This was followed by a more gradual decl ine to par tur i t ion when the level was the same as at mat ing (P>0.05). This low level was main ta ined for 20 days after partur i t ion.

Relationship between the progesterone levels in plasma and milk. T h e r e was a very close corre la t ion between p roges te rone levels in plasma (x) and in milk (y) dur ing the first mon th o f gestation (r=0.9410) and the regression equa t ion y= 5.6940x--3.7409 was calculated. This indicates that the milk level was about six times grea ter than that o f plasma.

Levels of oestradiol-17fl in plasma and milk During thefirst month of pregnancy. The assay resuhs for oestradiol-17fl in b lood

and milk samples of 12 cows at the beg inn ing of p regnancy (Fig. 3) showed similar

100

90

80

70

7" 601 i

,, 501

,~ 4o t -~ -~ I

20

10

1 I I I I [ L~ J - - - - I

0 0 2 4 6 8 10 1~2 14 16 1L8 ?0 2'2 2'4 26 2; 3L0

Mating Time (days)

Fig. 3. Concentrations of plasma and milk oestradiol-17fl during the first month of pregnancy ( n= 12). Milk oestradiol-1713 (C)) ; plasma oestradiol-1713 (@).

REPRODUCTIVE PATTERNS OF THE YAK Ill. 599

first and second peaks to those of non-pregnant cyclic cows (P>0.05), (see Yu et al., 1993). There was a third peak of plasma oestradiol-17fl in pregnant cows on days 13-16 [22.61 (st) 8.43 pg ml -l on day 16], which decl ined gradually to the baseline by day 22. The milk oestradiol-17fl rose abruptly from day 11, reached a peak value on day 16 [63.64 (st) 33.29) pg ml -I] and decl ined to the baseline on day 23. Hereafter, the levels in both plasma and milk rose gradually and were as high as 21.25 (sx) 7.65) pg ml -~ and 73.21 (SD 21.08) pg ml -l respectively on day 30.

During the zohole of pregnancy and the periparturient period. Mean values for oes- tradiol-17fl from 12 cows are shown in Fig. 4. The plasma level on day 30 of 20.04 (SD 8.41) pg ml-' was similar to that on the day of mating [22.30 (so 8.12) pg ml -~, /)>0.05]. It d ropped sharply at day 60 [10.84 (SD 6.95) pg ml-', P<0.05] before ris- ing gradually to a height of 46.64 (SD 11.70) pg ml-' on day 210. It increased significantly at day 239 (P<0.05) and progressively to a peak 551.4 (SD 70.86) pg ml -~ at parturi t ion before decl ining abruptly and very steeply (P<0.05) to the low level of 17.84 (so 6.63) pg ml -~ on day 1 after parturition. This low level was main ta ined for 20 days after parturit ion.

Re.lationship between the oestradiol-17fl level in plasma and milk. There was a mod- erately close correlation between oestradiol-17fl levels in plasma (x) and milk (y) dur ing the first mon th of pregnancy (r=0.6193) and the regression equat ion y= 1.0148x+42.9085 was calculated. This indicates that the milk concentrat ions were about four times greater than those in plasma.

600

500

40(

~" 3o(

20,

~ loo

,~ 80

40

20

3'o 6'0 do 18o' 21o' 24o'"' -10 -5 0 1

Mating Parturition Time (days)

oestradiol-17fl during the Fig. 4. Concentrations of plasma periparturition period (n=8).

I I I I

5 10 15 20

whole pregnancy and

600 BRITISH VETERINARY JOURNAL, 149, 6

Table I The ratio of progesterone (P4) to oes~radiol (Ez) in the plasma of

eight cows during the periparturient period

Periparturient Concentration (ng mg 1) Ratio period P4 /E,,. (days or hours) P4 E,~ (number of animals)

234(D) (5) 11.15 0.042 265.48 239(D) (6) 8.34 0.059 141.36 244(D) (6) 6.47 0.068 95.15 249(D) (5) 5.70 0.090 63.33 252(D) (8) 4.07 0.142 28.66 253(D) (8) 1.75 0.252 6.94

0(D)*(8) 0.34 0.515 0.66 3(H) (6) 0.32 0.281 1.14 7(H) (7) 0.50 0.098 5.68

15(H) (7) 0.50 0.032 15.63 I(D) (8) 0.30 0.018 16.67 3(D) (8) 0.26 0.017 15.29 5(D) (8) 0.31 0.019 16.32

10(D) (8) 0.41 0.016 25.53 15(D) (8) 0.25 0.011 22.73 20(D) (8) 0.24 0.018 13.33

*parturition; D, day; H, hour; P4, progesterone; E,,, oestradiol.

The relationship between progesterone and oestradiol-1 7fl in p lasma dur ing the periparturient period

Table I shows the progesterone and oestradiol-17fl concentrations and the progesterone/oestradiol (Pa/E=,) ratios measured in eight cows during the periparturient period. It indicated that the ratio of P4/E,~ was extremely high (265.5) on day 234 of pregnancy but declined abruptly (P<0.05) and dropped to the minimum at parturition (day 0). The ratio increased rapidly again after par- turition, reached 16.7 one day later and maintained this level for 20 days following parturition.

The correlation between the plasma progesterone (y) and plasma oestradiol- 17fl (x) within 20 days before parturition was significant (r=-0.8446). The regression equation was y=8.5107-18.6261 x.

DISCUSSION

The progesterone patterns during pregnancy and the periparturient period are similar to those of the dairy cow (Short, 1958; Donaldson et al., 1970; Stabenfeldt et al., 1970; Schams et al., 1972). In comparison with our previous report on cyclic yak cows (Yu et al., 1993), it is seen that the progesterone levels in plasma and milk increase gradually in the first 14 days both during the oestrous cycle and in early pregnancy. However, on day 15, the progesterone level of the cyclic cow reaches its peak, in contrast to that of the pregnant cow, in which it drops slightly. From day 16 onwards the progesterone level of the cyclic cow declines, while that of the

REPRODUCTIVE PATTERNS OF THE YAK III. 601

pregnant cow rises to maintain a high level after day 19 and is signific~intly higher than in the cyclic cow. This characteristic may be used for early pregnancy diag- nosis. The re-ascent of progesterone concentration on day 16 after a drop on day 15 might be a sign of pregnancy recognition as described by Heap and Flint (1984).

It has been reported (Bedford, 1972) that in the sheep and the guinea-pig pro- gesterone is mainly produced by the corpus luteum during early gestation, but by the placenta during late gestation. In the present study the level of blood pro- gesterone in the yak declined on day 90 and increased again on day 150, similar to that of the guinea-pig (Challis et aL, 1971). This may be due to decreased secretory function of the pregnancy corpus luteum by day 90; the function of the pregnancy corpus luteum being enhanced by the placenta, as in the sheep and guinea-pig, on day 150. This mechanism needs further study.

From the oestradiol-17fl profiles in the yak oestrous cycle (Yu et al., 1993) and early pregnancy we would suggest that the third peak in early pregnancy occurs later than that in the oestrous cycle; this characteristic is similar to that of the dairy cow (Huang et al., 1987).

The peak of oestradiol-17fl in the dairy cow occurs on the day before partur- ition (Chew et al., 1979; Kaker et al., 1984), or on the day of parturition (Stellflug et al., 1978; M6stl et al., 1981). The result of the present study agrees with the latter view. The sharp rise of oestradiol-17fl at parturition may be the cause of the pro- nounced increase in uterine blood flow, as in the dairy cow, which will benefit delivery. At the same time in the yak the progesterone level declines abruptly and the ratio of P4/Ez declines markedly. This is obviously different from the horse (Lovell, 1975), guinea-pig (Bedford, 1972) and women (Yannone et al., 1969), but similar to sheep (Basset & Thorburn, 1969; Challis, 1971), dairy cow (Donaldson et al., 1970; Stabenfeldt et aL, 1970) and rat (Csapo et al., 1969). The 'progester- one-block' hypothesis may explain the mechanism regulating onset of parturition.

ACKNOWI.EDGEMENTS

This research was supported by the International Foundation for Science (Grant No. B/1424-1) and International Atomic Energy Agency (Research Contract No. 5102/RB). The authors gratefully acknowledge the assistance of Professor G. H. Arthur with the English text.

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(A ccepted for publication 2 April 1993)