Conception Rates in Dairy Cattle from Services at Various Intervals after Parturition

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Abstract
Three groups of 50 cows each, bred 60 days or less, 61-90 days, and more than 90 days postpartum, showed a conception percentage from the 1st service of 48, 70, and 76%, respectively. Among the 50 cows bred 60 days or less, 24 were bred 50-60 days after parturition and 66.7% conceived, but only 30.8% conceived from the 26 bred 50 days or less postpartum. The difference in results for 50 days or less was highly significant. Additional services required for the fertile cows which did not conceive from the 1st service were considered. Including all services to fertile cows, the average number of services per conception were: first service 50 days or less after parturition 2.52; 51-60 days, 1.65; 61-90 days, 1.55; and over 90 days, 1.54. The high rate for cows bred 50 days or less after parturition was statistically highly significant. Although the average time from parturition to 1st service was only 40.9 days for the cows bred 50 days or less postpartum, the actual average days from parturition to conception was 100.5 days, which was decidedly longer than the 74.5 days for the cows 1st bred from 51-60 days and 93.8 days for the group with first service from 60 to 90 days after calving. In this experiment, in which cows with unquestionably good genital health were used, the results for rate of conception from first service, average number of services per conception, and the average days from parturition to conception indicated that the 1st service should be over 50 days postpartum. There was no difference in the number of sterile cows, abortions, retained placentae and metritis. Also there was no difference in the above factors at the next calving and none in conception rate and average time required for the next pregnancy.

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