PSIV-7 Multi-Sire Artificial Insemination of Beef Heifers in the Nebraska Sandhills May Increase Pregnancy Rate Compared with Single-Sire Insemination

Abstract

Abstract The objective of these studies was to observe pregnancy outcomes resulting from artificial insemination (AI) with multi-sire semen (MS) compared with single-sire semen (SS) in beef heifers. One study compared MS AI to SS AI and the other study observed the pregnancy rate to AI using sexed MS semen. In the first study, three bulls were selected for AI of 441 heifers in year one. Heifers were synchronized with the melengestrol acetate – PGF2α – GnRH protocol using estrus detection and timed AI. Seventy-five single-sire straws of semen, from each bull, were labeled A, B, or C. Remaining semen was pooled together to form multi-sire semen straws. Heifers were artificially inseminated using alternating treatment of MS or SS; A, B, or C. Ultrasound determined pregnancy rate of heifers by treatment averaged 63% ± 5.5% (SS-A), 64% ± 5.5% (SS-B), 65% ± 5.5% (SS-C), and 69% ± 3.3% (MS). Heifers administered MS averaged 4.5% ± 4.5% greater than SS (P = 0.32) and 5.9% ± 6.4% greater than the least performing sire (P = 0.36). The observed differences between MS and SS pregnancy rate are less than previous research suggests. It is hypothesized the best fertilization period for a sire and dam may differ between individuals and herds leading to variability in pregnancy rates. In the second study, multiple unproven bulls were selected for AI of 868 ± 37 heifers over two years. Heifers were synchronized using the previously mentioned protocol with split-time AI. Semen was collected and sexed to favor heifer progeny at an expected ratio of 9:1. The sexing process has been shown to decrease pregnancy rate due to sperm damage and decreased quantity. Semen from 3 random bulls were pooled together making 4 pools or 3 pools of multi-sire semen straws in year 1 and 2 respectively. Multi-sire sexed semen was only administered to heifers who exhibited estrus. The observed ultrasound determined pregnancy rate of heifers administered multi-sire sexed semen was 65% in year 1 and 75% in year 2, which is 12% and 22% greater than the average pregnancy rate reported in previous studies using single-sire sexed semen. Observed differences lends credence to the possibility of improving pregnancy rate by utilizing multiple sires for AI when semen quality is lower. Ultimately these two studies may suggest that multiple sires may outperform pregnancy rate of single sires to AI. This difference may be more pronounced when semen quality is lower. Further research into semen quality of single sires and pooled semen could lead to optimization of fertilization among individuals within a herd.