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Recent Advances in Reproductive Efficiency

Present Status of the Repeat-Breeder Cow Problem¹

Department of Genetics, University of Wisconsin, Madison

ABSTRACT

A repeat-breeder is defined as a clinically normal cow which, other factors being optimal, shows a reduced probability of conception. Both fertilization failure and embryonic loss are major causes of repeat-breeding. Much of the embryonic loss occurs between Days 16 and 25 after breeding. Nonspecific infection and undetermined after-effects, other than gross clinical pathology, have not appeared to be major causes. The uterus of the repeat-breeder during the luteal phase of the estrual cycle appears to be more resistant to bacterial invasion than that of the first-service animal, possibly indicating a deficiency of progesterone action. Therapy with progesterone, however, has not given clear-cut evidence for lessening of repeat-breeding. Poorly developed corpora lutea produced experimentally have been demonstrated to increase embryonic loss.

Experimentally produced antibodies have been shown to bring about fertilization failure and, in a somewhat lesser concentration, embryonic loss if they come in direct contact with the sperm. High planes of feeding appear to increase the incidence of breeding difficulties. Genetic causes of lowered fertility have been demonstrated, but heritability is relatively low. The degree of heritability in the Holstein breed may be high enough to give preference to certain A.I. sires on the basis of the breeding performance of their daughters.

¹ Paper No. 833 from the Division of Genetics.

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