Indications of breed by environment interaction for lamb weights in Norwegian sheep breeds

With high variation in environmental conditions, especially during the extensive grazing season, genotype by environment interaction is potentially important to lamb production in Norway. Using breed as an indicator of genotype, the interaction between breed and environment, i.e. production level of farm and year calculated as solutions of a random farm*year variable, on 52 farms keeping both long-tailed Dala and short-tailed Spæl during 1989–98 was studied. The dataset included 48,946 Dala lambs and 38,299 Spæl lambs. The breed by environment interaction affected lamb autumn weights, and though Dala lambs were always heavier, the difference was substantially smaller at lower than at higher production levels: 1 kg increase in production level was related to Dala lambs’ weights increasing 0.09 kg more than the Spæl lambs’ weights. The results indicate that breed by environment interaction may be of importance, and potential bias in the data and need for further research is discussed.