An experiment involving twenty multiparous Holstein cows was designed to study the pituitary-ovarian relationship in periparturient cows. The cows were divided into four equal groups. One group was slaughtered between 260 and 265 days of gestation; the second group was slaughtered within 18 hr following parturition; the third group was slaughtered 21 days post partum and the fourth group received 100 mg of progesterone daily for 20 days starting from the day of calving and was slaughtered on Day 21. There was no detectable amount of progesterone in the corpora lutea of pregnancy on the day of calving. An average of 26 μg/g progesterone was present in the corpora lutea of ante-partum cows. The corpora lutea were significantly larger in the ante-partum group than in the day-of-calving group. A significantly higher fsh level and lower lh level was found in the pituitaries of the day-of-calving group. Follicular size was significantly lower in the ante-partum and day-of-calving group as compared to both the post-partum groups. Injection of progesterone produced no significant alterations in fsh and lh levels of the pituitary glands. Neither did it depress ovarian follicular growth.
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