The objective of this study was to explore genotype by environment interactions (GxE) and macro-environmental sensitivity in a multi-breed sheep population. Post-weaning weight (PWWT), post-weaning
growth rate (PWGR), post-weaning scanned fat depth (PCF), carcase weight (CWT) and intra-muscular fat
(IMF) were investigated. The number of sheep analysed ranged from 28,860 for PWWT to 14,969 for IMF.
Environment was defined by the best linear unbiased estimation (BLUE) of contemporary group effects in an
animal model, using PWGR as the response variable. Each trait was analysed using a trivariate mixed effects
models which considered performance in low, average and high growth environments as separate traits.
Reaction norms were also used for each trait to estimate macro-environmental sensitivity as well as provide
an alternative method for estimation of GxE.