The Nature of Reproductive Failures in Cows of Low Fertility

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Abstract
The study covered 104 cows, 49 Guernsey and 55 Holstein. Each 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: breed; Bang''s disease; number of previous services; number of previous calvings; herd size; and herd breeding index. Appreciable effects upon the fertilization rate were noted for the 1st and the last 3 factors, and upon embryonic death rate for the 2d and the last 3. Visible genital abnormalities were found in 10.6% 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%) than in the Guernsey (2%). The total percentage of cows with genital abnormalities, 10.6, included 8.7% 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 3 main categories on the basis of reproductive performance during the first 34 days after breeding: failure of fertilization, 39.7%; embryonic abnormalities and mortality before 34 days, 39.2%; and embryos still normal at 34 days, 21.1%.

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