Data describing first parity reproductive and maternal performance and herd longevity of 655 cows, born over a 20-year period, were used to estimate genetic response in these traits, associated with selection for increased 365-day weight. The data were analyzed by least squares with the effects of year of cow birth, management regime during cow growth to 365 days of age, age of the cow's dam and regression on weaning age included in the model. Annual genetic change was estimated by comparing successive progeny groups of individuals with the remainder of the population. The only significant genetic trends were for 365-day weight (6.83 kg/yrj P.C.05) , dystocia score (-.40 units/yrj P<.05) and number of calves weaned in a standardized lifetime of 5.17 years (.33 calvesj P_< .01) . Though the data did not allow definitive conclusions concerning changes in maternal and longevity traits, there was evidence that selection solely for weight may be associated with increased mature body weight, delayed sexual maturity, decreased dystocia rate, increased progeny weights and decreased herd longevity.
Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume XII. Biotechnology, selection experiments, parameter estimation, design of breeding systems, management of genetic resources., , 205–209, 1986
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