Relationships among Luteinizing Hormone, Estradiol, Progesterone, Glucocorticoids, Milk Yield, Body Weight and Postpartum Overian Activity in Holstein Cows

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Abstract
Variables affecting postpartum ovarian function were evaluated in 28 Holstein cows allotted to three groups according to interval from parturition to first ovulation. Cows allotted to Group I ovulated between 9 and 14 days postpartum, those allotted to Group II ovulated between days 15 and 20 postpartum and those in Group III ovulating after day 20. During week 1 postpartum, serum estradiol concentration was lower (P<.01) in cows in Groups I and II compared to those in Group III. During week 2, serum estradiol levels were similar among cows that had not ovulated, but more (P<.05) cows in Groups I and II had palpable ovarian follicles ≥ 10 mm in diameter compared to cows in Group III. Number of episodic LH peaks and average LH concentration in blood samples collected at 15-min intervals for 4 hr on day 7 and day 14 were inversely associated with interval to first ovulation. Cows in Group I had more LH peaks and higher average serum LH levels on days 7 and 14 than cows in Groups II and III. Cows in Group II had more (P<.05) episodic LH peaks on days 7 and 14 compared to cows in Group III, but average LH concentration was not different (P>.10). Serum glucocorticoids were not significantly different among groups. Overall, interval to first ovulation averaged 17.6 ± 1 days (range 9 to 34). Serum progesterone remained less than .2 ng/ml from parturition until 2 to 3 days after first ovulation, when it increased (P<.05) to greater than 1 ng/milliliter. Cumulative change in body weight did not differ among groups during the first 6 weeks postpartum, but daily milk yields during the first 42 days postpartum were greater for cows in Group III. Lactation demands associated with increasing milk yield may have inhibited LH secretion and delayed onset of postpartum estrous activity. Copyright © 1979. American Society of Animal Science . Copyright 1979 by American Society of Animal Science.