The Relation of the Post-Partum Breeding Interval to Reproductive Efficiency in the Dairy Cow

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Abstract
A study of 1674 pregnancies in 593 cows of the University of Illinois dairy herd showed that: A mean of 1.97 services were required per conception, and the mean post-partum interval to first service was 117 days. The standard deviation of services per conception was 1.60 and of post-partum interval was 53.3 days. Fertility increased with the length of the post-partum interval to first service up to 100 to 120 days. In the cows bred less than 20 days after calving only 35 percent of the services resulted in conceptions, while nearly 58 percent of the services were effective in those cows bred 100 to 120 days after calving. Reproductive efficiency for the cows first bred 120 to 200 days after calving remained fairly constant, but those first bred more than 200 days after.
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