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Effect of Two Services during Estrus on the Conception Rate of Dairy Cows¹

New Jersey Agricultural Experiment Station, Sussex

ABSTRACT

It has been rather definitely established that the highest conception rates in dairy cows are obtained by natural or artificial service toward the end of the standing heat period (7). However, a demonstrated variability in the time of ovulation (2, 7) may result in failure to conceive with late-ovulating cows, because of possible exhaustion of spermatozoa. Early reports (1,3) indicated a striking advantage in double insemination. With limited data, Trimberger and Davis (8) declared double services to be impractical, after finding only a slight increase (82.5 to 84.0%) in nonreturns to first service of cows bred in the middle of estrus only, or rebred in 24 hr. To test the effect upon conception rate of double services during a single heat period, this project was initiated at the New Jersey Agricultural Experiment Station several years ago.

Beginning on January 1, 1953, a random sample of heifers and cows of the Holstein and Guernsey breeds of the Station herd were artificially inseminated twice during the same heat period.

¹ Paper of the Journal Series, New Jersey Agricultural Experiment Station, Rutgers University, the State University of New Jersey, Department of Dairy Science, New Brunswick. This investigation was supported in part by funds provided through collaboration with the Northeastern Cooperative Research Project NE-1.