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

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Abstract
Data from 184 Holstein heifers representing 6 sire lines and 4 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 significantly affected 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 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 1st calving (-0.31, P <.01) and also with 90-day milk production (-0.18, P < .05) and the average 90-day butterfat percentage (-0.31, P <.01) of the 1st 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 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).[long dash]Authors.

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