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

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-too. weight (--0.56, P < .01) and 6-to 12-too. weight gain (--0.22, P < .05). After adjusting puberal ages for 6-too. 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-O heifers (outbred animals from outbred dams), those born in the spring had the earliest age at puberty.