Latent Effects of Pregnancy on Postpartum Estrous Cycle Length in Dairy Cattle

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Abstract
This study involved 110 high producing dairy cows in three University herds. Rectal examinations were performed at twice weekly intervals from 5 to 60 days postpartum. The corpus luteum of pregnancy regressed rapidly during the early postpartum period and was usually not palpable after 14 days postpartum. There was an insignificant difference of 0.6 days (P>.05) in the interval from parturition to first estrus, depending on whether the first ovulation occurred on the same side or on the opposite side of the postgravid uterine horn and the regressing corpus luteum of pregnancy. A nonsignificant difference of 1.0 days (P>.05) occurred in the interval from first ovulation to second ovulation, depending on whether the second ovulation occurred on the same side or the opposite side of the postgravid uterine horn and regressing corpus luteum of estrus. The interval from first to second ovulation was 3.7 days shorter than the interval from second to third ovulation (P<.01). These observations indicate that pregnancy and the postgravid involuting uterus do not exert a unilateral influence on the interval to first postpartum ovulation and the length of the subsequent estrus cycle; however, there is a bilateral carry-over effect early in the postpartum period which shortens the interval from first to second ovulation.

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