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Effect of Sire Fertility and Timing of Artificial Insemination in a Presynch + Ovsynch Protocol on First-Service Pregnancy Rates

J. M. Cornwell^*, M. L. McGilliard^*, R. Kasimanickam and R. L. Nebel^*,1,2

^* Department of Dairy Science, and
Department of Large Animal Clinical Sciences, Virginia Polytechnic Institute and State University, Blacksburg 24061

¹ Corresponding author: rnebel{at}selectsires.com

Sire fertility may influence pregnancy rate (PR) by differences in sperm survival in the female reproductive system and time required for capacitation and transport of sperm to site of fertilization. A predicted fertility index, Estimated Relative Conception Rate, was used to select 3 high-fertility artificial insemination (AI) sires (+3) and 3 average AI sires (–1). Ovulation can be predicted to occur at approximately 28 h following GnRH administration when used in an Ovsynch protocol. The objective of this study was to determine if AI at 2 times, 0 or 24 h after GnRH administration, in a Presynch + Ovsynch protocol resulted in different first-service PR when average or high-fertility sires were used. Lactating Holstein cows (n = 1,457) from 2 dairy herds located in the Piedmont region of North Carolina were utilized for 12 mo. Timing of AI did not affect first AI PR and no interaction of sire-fertility group and timing of AI was detected. First AI PR did not differ between sire-fertility groups (23.2 vs. 29.4%) for average and high-fertility groups, respectively. First-lactation cows were 53% more likely to conceive than older cows, and cows bred during April through June were 66% less likely to become pregnant compared with cows bred from October through January. No interactions were detected among parity, season, sire-fertility group, or time of AI. Using only 3 sires per group based on Estimated Relative Conception Rate estimates resulted in large variability of sire conception within groups, although group averages differed by 6 points.

Key Words: sire fertility • timing of artificial insemination • estimated relative conception rate • Presynch + Ovsynch

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