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The Nature of Reproductive Failures in Cows of Low Fertility¹

University of Wisconsin, Madison

ABSTRACT

The study covered 104 cows, 49 Guernsey and 55 Holstein, each of which had been bred from 4 to 13 times without conceiving. The percentage of genitally-normal cows having fertilized ova when slaughtered at 3 days -was 66.1, but at 34 days the percentage having normal embryos had dropped to 23.1, for an embryonic death rate of 65.1. Estimates were made of the effect of the following factors on fertilization and embryonic death: (a) breed, (b) Bang's disease, (c) number of previous services, (d) number of previous calvings, (e) herd size, and (f) herd breeding index. Appreciable effects upon the fertilization rate were noted for the first and the last three factors, and upon embryonic death rate for the second and the last three. Visible genital abnormalities were found in 10.6 per cent of the cows at the time of slaughter; these abnormalities were not detected by clinical examination. There was a higher occurrence in the Holsteins (18.2 per cent) than in the Guernsey (2.0 per cent). The total percentage of cows with genital abnormalities, 10.6, included 8.7 per cent in which the abnormality constituted a physical barrier to fertilization. Considering the group of cows as a whole, including those with genital abnormalities, division may be made into three main categories on the basis of reproductive performance during the first 34 days after breeding: (a) failure of fertilization, 39.7 per cent; (b) embryonic abnormalities and mortality before 34 days, 39.2 per cent; and (c) embryos still normal at 34 days, 21.1 per cent.

¹ Published with the approval of the Director of the Wisconsin Agricultural Experiment Station. Paper No. 383, from the Department of Genetics.

² The authors are deeply indebted to the Badger Breeders Cooperative, Shawano, Wisconsin, and its officers and veterinarians for making the experimental facilities and assistance available and for locating and furnishing the experimental animals. Thanks are due especially to Dr. W. H. Dreher for his willing assistance and cooperation throughout the experiment.