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The Effects of Infertile Insemination and Individuality of Bulls upon the Subsequent Fertility of Cows Returning for Service^{1, 2,}

Department of Genetics, University of Wisconsin, Madisonand the Bureau of Dairy Industry⁴

ABSTRACT

Two studies were conducted to determine the effects of the bull used on first service on the fertility of his return cows at second service.

Certain bulls used on first service may affect the conception rate of other bulls used on his return cows at later services. The lowered fertility produced in the cows by the first bull is much more apparent for low-fertility bulls than for average-fertility bulls.

There is a definite association between the average length of the return-interval and the fertility of the return cows at second service, long return-intervals being associated with low fertility.

¹ Paper no. 457 from the Department of Genetics, University of Wisconsin, Madison.

² The data for this study have been furnished by the Badger Breeders Coop., Shawano, Wis. and by the University of Wisconsin Department of Dairy Husbandry. The authors are indebted to W. H. Dreher and J. H. Webb of the Badger Breeders Coop, for their assistance in collecting a portion of the data.

³ Agent of the Bureau of Dairy Industry, U.S.D.A.

⁴ This work has been done under a cooperative agreement between the Wisconsin Agricultural Experiment Station and the Bureau of Dairy Industry, U.S.D.A. The funds contributed by the Bureau of Dairy Industry came as an allotment from the Research and Marketing Act.