Reaction norms for protein yield and days open in Swedish red and white dairy cattle in relation to various environmental variables

Various environmental variables were used in analysis of genotype by environment interaction (GxE) for first lactation protein yield and days open in Swedish Red and White dairy cattle. The environmental variables described the herd level of production and fertility, herd size, geographic position, and weather conditions of the herds. Fixed effects of the environmental variables were analysed using a fixed regression sire model. All studied environmental variables, except the average rainfall during summer, had significant effect oil both protein yield and days open. Possible effects of GxE were evaluated using random regression of protein yield and days open on the environmental variables. GxE was indicated between protein yield and herd level of production, protein yield and herd size, and days open and herd level of fertility. Correlations between the traits expressed at average and deviating levels of the environment were high indicating that GxE did not result in reranking of sires within the range of environments found in Sweden.