Relationships among Weight Gains, Age at Puberty and Reproductive Performance in Heifers

An experiment was conducted with 89 crossbred heifers to study the effects of varying feed level during a 153-day wintering period on subsequent growth and reproduction. Heifers were fed to gain either 0.23, 0.45 or 0.68 kg per day (designated L, M and H, respectively) during the wintering period. Increasing the winter feed level increased body weight, pelvic area and condition score by the end of the winter feeding period. Heifers on the lower winter feed levels gained more after being put out on summer grass but compensatory gains were not sufficient for them to attain the same body weight of heifers wintered at the high level. Increasing the winter feed level decreased age at puberty so that fewer of the L and M heifers were in estrus before the 60-day breeding season and fewer of the L heifers were in estrus before or during the breeding season. The effects of feed level on age at puberty were accounted for by differences in body weight but the three feed groups did not reach puberty at the same weight since increasing the feed level increased weight at puberty. Reproductive potential as measured by the proportion of heifers pregnant in October was lowest in the L group because: Fewer heifers were bred. Fewer heifers became pregnant that were bred. These heifers tended to conceive later. There was a higher pregnancy loss.