Genetic parameters of production, feed intake, body weight, body composition, and udder health in lactating dairy cows

Abstract

Records on milk yield, body weight, feed intake, SCC, mastitis incidence, and indicators of body composition were analysed both as repeated measures within lactations and as aggregated lactation measures. The data comprised 603 lactations on 293 dairy cows on an experimental farm in Denmark. Most genetic parameters were in agreement with similar results from the literature. Minimum body weight is reached earlier in lactation than peak yield and much before peak feed intake. Genetic selection for higher milk production will lead to cows with lower body weight gains during lactation and therefore cows that are less well prepared to meet the energy requirements of the subsequent lactation. There were positive genetic correlations between mobilisation of body reserves and SCC indicating that increased production leads to metabolic stress and a change in the immune system. Single trait selection for production will lead to increases in SCC and thereby in mastitis frequency. Cows with large fat depots had a higher milk production. However, selection for increased milk production leads to lower weight gains during lactation leaving the cow less well prepared for the next lactation. This study showed large variation in the variables attempting to describe the shape of lactation curves for milk yield, body weight, and feed intake. Therefore, encouraged continuation in recording these variables, and physiological measures to understand the fundamental biological complex of the energy balance in lactating dairy cows are needed. The variables for repeated measures within lactation may be analysed using random regression models in order to study feed forward mechanisms from records in early lactation to records in late lactation.