PS2-12. Semen Use and Fertility by Service Number in Dairy Heifers from Commercial Farms in Wisconsin.

Abstract The objective of this study was to characterize reproductive management strategies in dairy heifers on commercial farms in Wisconsin using large-scale field data. A retrospective observational study was conducted using artificial insemination (AI) records extracted from farm management software system (Dairy Comp). Data were collected from 45 commercial dairy farms in Wisconsin between January 2021 and December 2024 and included 82,905 AI service events in heifers. A total of 202 records (0.2%) corresponding to natural services were excluded from the analysis. Variables extracted included service number, timing of insemination, semen type, and pregnancy diagnosis for each service. Services were classified as first (n = 43,950), second (n = 21,288), third (n = 9,814), or fourth or greater (4th+; n = 6,575). Semen utilization varied markedly by service number. For first services, 82.2% used sexed semen from dairy breed sires, 12.7% used conventional semen from dairy breed sires, and 5.1% used conventional semen from beef breed sires. For second services, the distribution was 72.6%, 19.6%, and 6.3%, respectively. For third services, use of sexed semen declined to 41.6%, whereas conventional dairy and beef semen increased to 30.4% and 28.0%, respectively. By fourth or greater services, only 11.7% used sexed semen, whereas 36.5% and 51.8% used conventional dairy and beef semen, respectively. Pregnancy per AI (P/AI) differed by semen type and service number. At first service, P/AI was similar between sexed and conventional dairy semen (53.9% vs. 56.6%) but lower than that achieved with conventional beef semen (66.6%). For subsequent services, AI using sexed semen consistently resulted in the lowest P/AI (48.6%, 44.4%, and 37.5% for second, third, and fourth+ services, respectively). In second and third services, conventional beef semen yielded greater P/AI compared with conventional dairy semen (62.8% vs. 58.1% and 61.5% vs. 55.2%, respectively). In fourth or greater services, P/AI was similar between conventional beef and dairy semen (48.7% vs. 48.9%). In conclusion, reproductive management strategies in dairy heifers shift from predominant use of sexed dairy semen at first service toward increased use of conventional and beef semen at later services, with this transition aligning with differences in fertility outcomes across service numbers. These results underscore the importance of strategic semen selection and service planning to optimize reproductive performance in dairy heifers.