Short Communication: Conception Rates Following Detection of Estrus and Timed AI in Dairy Cows Synchronized Using GnRH and PGF2α

The objective of this study was to compare conception rates of cows exhibiting spontaneous estrus and receiving artificial insemination (AI) before completion of a timed AI protocol with cows that did not display estrus spontaneously, but were inseminated after 1 of 3 GnRH-PGF2α protocols. Cows (n = 432) in 2 herds were administered GnRH on d -7 and were tail-chalked daily. Cows detected in estrus before d 0 were inseminated immediately. Cows not detected in estrus by d 0 were administered PGF2α and were tail-chalked daily until 48 h after PGF2α. Cows detected in estrus from d −7 to 48 h after PGF2α were inseminated and designated as treatment A (n = 46). Cows not detected in estrus and not inseminated by 48 h after PGF2α were assigned randomly to receive either GnRH 48 h after PGF2α and timed AI 16 h later (treatment B; n = 132), or GnRH and timed AI 64 h after PGF2α (treatment C; n = 127), or timed AI 64 h after PGF2α (treatment D; n = 127). Pregnancy was diagnosed 38 to 45 d after AI by palpation per rectum of uterine contents. Nearly 11% of all cattle exhibited spontaneous estrus and received immediate AI. Herd did not influence the percentage of cows detected in estrus and inseminated. Conception rates did not differ among treatments. Conception rates differed between herds, but no interaction of herd × treatment was detected. No differences were detected between herds for days in milk, milk production, AI service number, or parity.