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Variation in Estrual Cycles of Holstein-Friesian Cattle¹

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

ABSTRACT

The lengths of intervals between estrual periods were studied in a herd which consisted of six sire lines of breeding and in which four systems of mating were practiced. The distribution and mean lengths of 766 estrual cycles and 191 return intervals from 221 heifers differed significantly (P < 0.05). The mean lengths were 22.3 days for estrual cycles and 25.3 days for return intervals. A repeatability estimate of estrual-cycle lengths was calculated for the heifers in each sire line and system of mating. Repeatabilities ranged from zero to 0.29 for the sire lines and from 0.02 to 0.21 for the systems of mating.

An analysis of variance showed estrual-cycle length in heifers to be affected significantly by the season of birth and the system of mating. The summer- and spring-born heifers had the longest cycles, 25.0 and 25.2 days, whereas the winter- and fall-born had cycles averaging 22.2 and 20.9 days, respectively. Daughters of inbred dams had the longest mean cycle lengths, 24.9 days for the outbred daughters and 25.6 days for the inbred; daughters of outbred dams averaged 20.6 for those that were outbred and 22.2 for those that were inbred.

An analysis of variance of the first estrual-cycle length following calving in outbred and inbred cows showed a significant interaction of sire line and system of mating. Repeatability estimates of the first estrual-cycle length following calving from one calving interval to another of 0.11 (P < 0.10) for the outbreds and 0.06 for the inbreds were calculated.

¹ From the Department of Genetics (Paper No. 816) and Department of 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 and by a grant from the Emmons Blaine, Jr., Fund. 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 Cattle Research Branch, USDA.

² Agents of the Dairy Cattle Research Branch, USDA.