Factors Affecting Estrous Exhibition and Conception following n Single Administration of in Dairy Cows

This study determined the effects of several reproductive factors at prostaglandin $F_{2{\alpha}}\;(PGF_{2{\alpha}})$ administration on the subsequent estrous exhibition and conception. Three hundreds and twenty six dairy cows in seven dairy herds received a 25 mg $PGF_{2{\alpha}}$ after confirming the presence of corpus luteum (CL) by ultrasonography, and the cows exhibited estrus within 7 days following $PGF_{2{\alpha}}$ administration were artificially inseminated (AI). Two hundreds cows among the 326 cows received additional ultrasonography at $PGF_{2{\alpha}}$ administration to measure the diameters of the largest follicle and CL on ovaries, and blood samples collected from the cows were analyzed for serum progesterone (P4) level. Cow parity, days open, body condition score (BCS), season and herd variables were recorded. Of the treated 326 cows, 171 cows (52.5%) showed estrus within 7 days after treatment, and the conception rate following AI was 37.4% (64/171). There were significant differences on the estrous exhibition ($31.3{\sim}65.8%$, p<0.01) and conception rates ($23.1{\sim}66.7%$, p<0.05) among the herds, while cow parity, days open, BCS and season did not affect the subsequent estrous exhibition and conception rates. The diameters of the largest follicle and CL on ovaries, and serum P4 level at the $PGF_{2{\alpha}}$ administration were not related to the subsequent estrous exhibition and conception. The results indicate that the improved outcomes of synchronization of estrus using a single $PGF_{2{\alpha}}$ administration may be related to the appropriate management of the herd.

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