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The Effects of Bull Urine on Puberty and Calving Date in Crossbred Beef Heifers^1,2,

North Carolina State University, Raleigh 27650

Abstract

The effects of bull urine on the percentage of heifers reaching puberty and on subsequent calving dates were examined with 52 crossbred beef heifers. Heifers were palpated for ovarian condition and classified as prepubertal or pubertal before (Palpation I) and after (Palpation II) eight weekly oronasal treatments with bull urine or water. A larger percentage of urine-treated than water-treated heifers reached puberty during the experimental period (67 vs 32%; P<.05), supporting the hypothesis that bull urine contains a priming pheromone. Body weight of urine-treated heifers that did not reach puberty by Palpation II was lower than that of water-treated heifers that did not reach puberty (P<.05), indicating that an association exists between body weight and the response to pheromonal cues in bull urine. There were no treatment differences in pregnancy rate after a 90-d breeding period, and no differences in pregnancy rate between heifers that had reached puberty before the breeding season started and heifers that had not reached puberty. Urine-treated heifers reaching puberty during the experiment calved earlier (P<.05) in the calving season than did water-treated heifers of the same category. The distribution of these calvings was also different (P<.01), resulting in a shorter calving season for urine-treated heifers. More heifers that had reached puberty by Palpation II calved in the first 20 d of the calving season than did heifers that had not reached puberty by Palpation II, regardless of treatment group (P = .02). There was a tendency for urine-treated heifers to calve earlier than water-treated heifers, with the exception of urine-treated heifers that had not reached puberty by Palpation II. These data support the hypothesis that there is a priming pheromone in bull urine that can hasten the onset of puberty in beef heifers.

¹ Paper No. 8140 of the Journal Series of the North Carolina Exp. Sta., Raleigh. The use of trade names in this publication does not imply edorsement by the North Carolina Agr. Exp. Sta. of the products named nor criticism of similar ones not mentioned.

² The authors express their appreciation to Dr. L. C. Ulberg and the personnel at the Reprod. Physiol. Res. Lab., North Carolina State Univ., for their assistance in carrying out this study, as well as the employees of the John Umstead, Unit, Dept. of Agr., Butner, NC. We also thank Clarence Marsh, Reprod. Physiol. Res. Lab., who performed the rectal palpations, and Dr. B. H. Johnson, Dept. of Anim. Sci., North Carolina State Univ., who performed the progesterone assays. L. C. Ulberg, J. Britt and H. Underwood provided many helpful criticisms of an earlier draft of this manuscript. This study constitutes part of the thesis submitted by MKI in partial fulfillment of the requirements for the Doctor of Philosophy degree at North Carolina State Univ.

³ Dept. of Zool.

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