Effect of Two Services during Estrus on the Conception Rate of Dairy Cows

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Abstract
A random sample of heifers and cows of the Holstein and Guernsey breeds of the Dairy Research Farm were artificially inseminated twice during the same heat period with either fresh or frozen semen. The first insemination was performed towards the end of standing heat, the second 12 to 20 hours later. Type of service and type of semen were random for each cow at each heat period. All services on all cows which utimately became pregnant were considered. Study of a total of 1028 services revealed that double-service increased conception rates from 53.7 to 56.1% with fresh semen, and from 50.4 to 52.7% with frozen semen. Chi-square analysis showed that differences between types of service and types of semen were not statistically significant. Double-service within the same estrus cycle can not be recommended on a routine herd-wide basis. Frozen semen has been used in the station herd without appreciably lowering conception rates. Future studies of this nature should concern themselves with difficult breeders and more varied and controlled intervals between double services.

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