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Variation in Some Factors Affecting the Length of Calving Intervals¹

Departments of Dairy Husbandry and Genetics, University of Wisconsin, and Dairy Husbandry Research Branch, USDA, Madison, Wisconsin

ABSTRACT

The causes of prolongation of the calving interval were studied for the intervals following 395 calvings of an outbred experimental Holstein-Friesian herd. Losses of time were attributed to one or more of the following conditions: (a) postpartum anestrus, (b) interruption of the estrual cycle, (c) out-of-breeding condition, (d) infertile service, and (e) loss of pregnancy. When averaged over the entire herd, these amounted to 0.3, 8.0, 5.2, 21.2, and 11.9 days, respectively. Cows for which it was necessary to delay breeding until the uterus attained breeding condition showed greater loss due to infertile service than did cows that did not requirs delay in breeding. More time also was lost due to out-of-breeding condition following abnormal, than following normal, calvings and by pluriparous, than by primiparous, cows.

¹ From the Departments of Genetics (Paper No. 688) and Dairy Husbandry, published with the approval of the director of the Agricultural Experiment Station. This study was supported in part by a grant from the Research Committee of the Graduate School from funds supplied by the Wisconsin Alumni Research Foundation. It is a contribution from the Wisconsin Agricultural Experiment Station as a collaborator under the North Central Region Cooperative Research Project, entitled "Improvement of Dairy Cattle Through Breeding—NC-2," conducted in cooperation with the Dairy Husbandry Research Branch, USDA.