SUMMARY Data from 272 cows bred at 35 days or less after calving, when compared with data from 405 cows bred 36 or more days after calving, indicated that early breeding resulted in almost as great a conception rate by the end of 3 services, did not cause abnormally long intervals between services, and did not result in more permanent infertility or in more abortions. Observations on 50,519 cows on which DHIA records were kept indicated that of the 2,723 cows bred at 40 days or less after calving, 3.3% fewer became pregnant at that or later services and had to be removed from the herds. There was no indication of any such effect, however, when cows were bred at 40 to 60 days after calving. Observations on 36,276 cows having at least 2 successive calves indicated that, on the average, cows were bred at 82.2 ± 33.7 days after calving and that each day of breeding sooner than that, down to 35 days, resulted in a calving interval shortened by a mean of 0.9 days.
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Durward Olds (1970) studied this question.