Reproductive Response of Beef Cows to Exogenous Progestogen, Estrogen and Gonadotropins at Various Stages Postpartum

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Abstract
The effects of three hormone treatments were studied at five intervals during postpartum anestrus in 97 pluriparous beef cows. The treatments consisted of feeding an orally active progestogen, progestogen treatment followed by an estrogen, and the progestogen treatment followed by gonadotropins. Treatment was started when the postpartum intervals were 5 to 10, 10 to 15, 20 to 25, 30 to 35 and 40 to 45 days. The interval lengths from calving to first estrus, first ovulation and conception were determined. In most cases the progestogen feeding followed by an estrogen had a greater effect than the other treatments in reducing the interval lengths to first estrus, first ovulation and conception, especially during the early postpartum intervals. Gonadotropin injections following the progestogen treatment did not decrease the interval from calving to estrus, ovulation and conception. Synchronization of estrus was highest in animals treated with an estrogen following the progestogen treatment, and in animals treated at mid postpartum anestrus (20 to 25 days). Conception rates at first service were highest in the treated animals which received the progestogen treatment and an estrogen injection on day 2 with no further treatment. When pooled, the treated animals had their highest percent conception at first service in the 30 to 35 day postpartum interval. Conception rates for treated and untreated animals were comparable by the third service. Copyright © 1972. American Society of Animal Science. Copyright 1972 by American Society of Animal Science

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