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J. Dairy Sci. 88:4313-4316
© American Dairy Science Association, 2005.

Short Communication: Conception Rates Following Detection of Estrus and Timed AI in Dairy Cows Synchronized Using GnRH and PGF2{alpha}

J. C. Dalton1, R. Manzo1, A. Ahmadzadeh1, B. Shafii2, W. J. Price2 and J. M. DeJarnette3

1 Animal and Veterinary Science Department, and
2 Statistical Programs, College of Agricultural and Life Sciences, University of Idaho, Moscow 83844
3 Select Sires, Inc., Plain City, OH 43064

Corresponding author: Joseph C. Dalton; e-mail: jdalton{at}uidaho.edu.

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-PGF2{alpha} 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 PGF2{alpha} and were tail-chalked daily until 48 h after PGF2{alpha}. Cows detected in estrus from d –7 to 48 h after PGF2{alpha} were inseminated and designated as treatment A (n = 46). Cows not detected in estrus and not inseminated by 48 h after PGF2{alpha} were assigned randomly to receive either GnRH 48 h after PGF2{alpha} and timed AI 16 h later (treatment B; n = 132), or GnRH and timed AI 64 h after PGF2{alpha} (treatment C; n = 127), or timed AI 64 h after PGF2{alpha} (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 x treatment was detected. No differences were detected between herds for days in milk, milk production, AI service number, or parity.

Key Words: conception rate • detection of estrus • synchronization • timed AI






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