Genotype by environment interaction for lamb weaning weight in two Norwegian sheep breeds

G. Steinheim ^1*, J. degård ¹, T. Ådnøy ¹, G. Klemetsdal ¹

¹ Department of Animal and Aquacultural Sciences, Norwegian University of Life Sciences, Ås, Norway

^* To whom correspondence should be addressed. E-mail: geir.steinheim{at}umb.no.

	Abstract

Genotype by environment interaction (GxE) effects on live weaning weights of lambs were studied, using the two breeds Norwegian White sheep (NWS) (heavy, long-tailed) and Spel sheep (Spel) (lighter, short-tailed) as genetic groups (G); 37,338 NWS lambs and 30,075 Spel lambs born 1989 to 1999 on 40 farms keeping both breeds together were included in the analyses. Environment was characterized by farm*year (E). In a mixed linear model framework, significance of the random GxE effect and breed-specific environmental variances were tested using a log-likelihood approach. Directions and magnitudes of the effect were described through variance component estimates. An across-genotype environmental correlation was also employed. There was a significant GxE effect on lamb weights: significant breed differences were found for variance of flock by year effects, indicating different phenotypic plasticities with changing flock by year environments, with the NWS being more sensitive to environmental change. Further, the breed-specific residual variance was higher for NWS, indicating that the effects of environmental variation were larger for the NWS breed's weaning weights within flock and year. Further, the correlation between flock by year effects for the two breeds was significantly different from unity (0.82±0.02), indicating that the common environment is "perceived" differently in the two breeds. The "best" environment for one breed is not necessarily "best" for the other breed, and vice versa. Solutions of flock by year effects may be used to describe how environmental characteristics such as climate and topography affect the production of different genotypes, and for clustering of environments, thus facilitating improvement of breeding programs and management schemes for domestic and wild ungulate populations.

Key Words: breed, genotype by environment interaction, phenotypic plasticity, sheep, weaning weight