Animal Reproduction (AR)
Animal Reproduction (AR)
Original Article

Estrous response and AI pregnancy rates of 2-year-old beef heifers exposed to androgenized steers before an estrous synchronization protocol with double injection of PGF2alpha

C. Fiol, R. Ungerfeld

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The objective of this study was to determine if exposure of 2-year-old beef heifers to androgenized steers (AS) for 30 days before the beginning of an estrous synchronization protocol (ESP) and artificial insemination (AI) increases the estrous response and pregnancy rate. Hereford x Braford heifers were stratified by body weight and presence of a corpus luteum (CL) and assigned to be 1) exposed to AS (EAS; n = 53) or 2) not exposed to AS (NE; n = 53) for 30 days (Day 0 = first day of exposure). Proportions of heifers with a CL on Day -7 were 20.6 and 24.5% for EAS and NE, respectively. Ovaries of each heifer were scanned on Days 15 and 30 of the exposure period for a CL. On Day 30, steers were removed from the EAS heifers and two doses of a PGF2alpha analogue were administered to each heifer 11 days apart. Heifers were observed for behavioral estrus for 6 days, beginning 48 h after the last PGF2alpha injection, and inseminated 12 h after estrus detection. More EAS than NE heifers had a CL on Day 15 (54.7 and 32.1%, EAS and NE, respectively; P < 0.02), but there was no difference in the proportion of heifers that had a CL by Day 30 (73.6 and 72.0%, EAS and NE, respectively; P = 0.2). There were no differences between EAS and NE heifers for proportions that showed estrus (66.0 and 67.9%, EAS and NE, respectively; P = 0.8), conception rates (83.0 and 92.0%, EAS and NE, respectively; P = 0.3) and pregnancy rates (83.0 and 86.5%, EAS and NE, respectively; P = 0.6). Exposing 2-year-old heifers to AS under the conditions of this experiment before an ESP that included a double injection of PGF2alpha had no effects on estrous response and AI pregnancy rates.


AI pregnancy rates, beef heifers, biostimulation, estrous synchronization
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