Genotype X environment interactions for early growth and ultrasonic measurements in hill sheep

Genotype X environment and genotype X sex X interactions were investigated using lines of Scottish Blackface sheep that had been divergently selected under intensive husbandry conditions for predicted carcass lean proportion, and offspring of rams from these selection lines which were reared under extensive hill conditions. Traits considered were live weight and ultrasonic fat and muscle depth. These were measured at 20 weeks of age on the intensively reared lambs and at 17 weeks of age on the extensively reared animals. Heritabilities for the two environments were 0.39 and 0.20 for fat depth, 0.36 and 0.25 for muscle depth and 0.23 and 0.22 for live weight. Genetic correlations between the environments were 0.54 (s.e. 0.17), 0.90 (s.e. 0.14) and 0.11 (s.e. 0.43) for fat depth, muscle depth and live weight, respectively. The extensive environment may be subdivided according to whether the lambs are reared on improved pasture or on the hill side. The genetic correlations (with s.e.s where estimable) between performance in these two environments were 0.70 (s.e. 0.33), 0.71 (s.e. 0.23) and 1.00 for fat depth, muscle depth and live weight. Genetic correlations between male and female performance under extensive conditions were 0.84 (s.e. 0.28), 0.99 (s.e. 0.14) and 1.00 for fat depth, muscle depth and live weight. For fat depth, the genetic correlations of the intensively reared lambs (males only) with extensively reared females and males were 0.37 (s.e. 0.22) and 0.67 (s.e. 0.17), respectively.