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Influence of Exposure to Bulls on Resumption of Estrous Cycles Following Parturition in Beef Cows¹

University of Nebraska², Lincoln 68583

Abstract

The effect of bull exposure on the resumption of estrous activity following parturition was studied in an experiment using mature Hereford and Hereford x Angus beef cows. In the spring of 1981 and 1982, cows were assigned by breed and calving date to one of two treatment groups. Cows were exposed to bulls either from 3 to 85 d postpartum (BE; n=45, 1981; n=35, 1982) or from 53 to 85 d postpartum (NE; n=39, 1981, n=36, 1982). Blood samples were collected from all cows once weekly from calving until 85 d postpartum to determine progesterone concentrations. The first increase in progesterone, which indicated onset of estrous cycles occurred at 43 ± 2 vs 63 ± 2 d (P<.01) in 1981 and at 39 ± 2 vs 61 ± 3 d (P<.01) postpartum in 1982 in BE cows and NE cows, respectively. Early postpartum exposure of cows to bulls reduced the postpartum anestrous interval.

¹ Published as Paper No. 7186, Journal Ser. Nebraska Agr. Exp. Sta. Anim. Sci. Dept. Acknowledgement is made to Jane A. Ossenkop and Lois V. Botts for assistance in preparation of this manuscript. Address requests for reprints to: J. E. Kinder, 218 Marvel Baker Hall, Univ. of Nebraska, Lincoln, NE 68583.

² Dept. of Anim. Sci.