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This Article Free Via Open Access Full Text Full Text (PDF) All Versions of this Article: jas.2006-849v1 85/7/1669    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Tauck, S. A. Articles by Berardinelli, J. G. Search for Related Content PubMed PubMed Citation Articles by Tauck, S. A. Articles by Berardinelli, J. G.

Putative urinary pheromone of bulls involved with breeding performance of primiparous beef cows in a progestin-based estrous synchronization protocol¹

Department of Animal and Range Sciences, Montana State University, Bozeman 59717

² Corresponding author: jgb{at}montana.edu

The objective of this study was to determine if factors associated with the biostimulatory effect of bulls alter breeding performance of primiparous, suckled beef cows using a progestin-based estrous synchronization protocol. We tested the hypotheses that the estrous synchronization response and AI pregnancy rates differ among cows exposed to bulls, continuously exposed to bull urine, and exposed to fence-line contact with bulls or cows not exposed to bulls or bull urine. Data were collected from 3 experiments performed over consecutive years. Cows were assigned to the following treatments: bull exposure (BE; n = 26) or no bull exposure (NB; n = 25) in Exp. 1, bull urine exposure (BUE; n = 19) or steer urine exposure (SUE; n = 19) in Exp. 2, and fence-line contact with bulls (BFL; n = 26) or no bull exposure (NB; n = 26) in Exp. 3. Synchronization protocols in each experiment included the use of a controlled internal drug release device (d –10), PGF₂ (d –3), and GnRH and fixed-time AI (TAI; d 0). Cows that were observed in estrus by 60 h after PGF₂ were inseminated 12 h later. Cows not observed in estrus by 60 h after PGF₂ were TAI at 72 h and given GnRH (100 µg). Pregnancy was determined by ultrasonography 35 d after TAI. In Exp. 1, 2, and 3, cows were exposed directly to bulls, bull urine, or bull fence-line contact for 35, 64, and 42 d, respectively. Data were analyzed between treatments within each experiment. The proportion of estrous cycling cows did not differ between treatments at the beginning of each experiment; however, more (P < 0.05) BE and BFL cows were estrous cycling at the beginning of the estrous synchronization protocol than NB cows in Exp. 1 and 3. The proportion of cows that showed estrus and interval to estrus after PGF₂ did not differ between treatments in Exp. 1 and 3. However, in Exp. 2, more BUE cows tended (P = 0.09) to have shorter intervals to estrus and to exhibit estrus after PGF₂ than SUE cows. Overall, AI pregnancy rates were greater (P < 0.05) for BE and BUE cows than for NB and SUE cows in Exp. 1 and 2, respectively. There was no difference in AI pregnancy rates between BFL and NB cows in Exp. 3. The presence of bulls and exposure to bull urine appeared to improve breeding performance of primiparous beef cows using a progestin-based estrous synchronization protocol, whereas fence-line bull exposure was insufficient to cause this biostimulatory effect. We propose that a novel urinary pheromone of bulls may be responsible for the enhancement of fertility in the primiparous, postpartum cow.

Key Words: biostimulation • bovine • breeding performance • controlled internal drug release device • pheromone • postpartum