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Some Factors Affecting Age at Puberty and the First 90 Days of Lactation in Holstein Heifers¹

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

ABSTRACT

Data from 184 Holstein heifers representing six sire lines and four systems of mating were analyzed to determine the genetic effects of sire-line and system of mating, and the environmental effect of season of birth on age at puberty. The mean age at puberty for this group of heifers was 345 days. Sire line and system of mating were found to affect significantly the age at which a heifer attained puberty. Age at puberty was correlated significantly with 6-mo. weight (–0.56, P < .01) and 6- to 12-mo. weight gain (–0.22, P < .05). After adjusting puberal ages for 6-mo. weight the significance of the effects of sire line and system of mating was removed. Calfhood scouring caused a delay in attainment of puberty which was significant in the fall-born heifers, in which the delay was 136 days. In the nonscouring 0-0 heifers (outbred animals from outbred dams), those born in the spring had the earliest age at puberty.

Age at puberty was correlated significantly with weight at first calving (–0.31, P < .01) and also with the 90-day milk production (–0.18, P < .05) and the average 90-day butterfat percentage (–0.31, P < .01) of the first lactation. Significant correlations existed for 6-mo. weight with calving weight (0.50, P < .01) and 90-day milk production (0.35, P < .01). Calving weight was correlated significantly with both the 90-day milk production (0.45, P < .01) and the average 90-day butterfat percentage (0.28, P < .01). Standard partial regression coefficients indicated that 90-day milk production was affected significantly only by calving weight (0.38, P < .01), whereas the average 90-day butterfat percentage was affected significantly by age at puberty (–0.25, P < .05) and calving weight (0.21, P < .05).

¹ From the Department of Genetics and Department of Dairy Husbandry. Paper No. 796 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 Agent of the Dairy Cattle Research Branch, USDA.