GENOTYPE X ENVIRONMENT INTERACTIONS FOR EARLY GROWTH AND ULTRASONIC MEASUREMENTS IN HILL SHEEP

Genotype X environment and genotype X sex X interactions were investig ated using lines of Scottish Blackface sheep that had been divergently selected under intensive husbandry conditions for predicted carcass l ean proportion, and offspring of rams from these selection lines which were reared under extensive hill conditions. Traits considered were l ive 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 ag e on the extensively reared animals. Heritabilities for the two enviro nments were 0.39 and 0.20 for fat depth, 0.36 and 0.25 for muscle dept h 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 ext ensive environment may be subdivided according to whether the lambs ar e reared on improved pasture or on the hill side. The genetic correlat ions (with s.e.s where estimable) between performance in these two env ironments were 0.70 (s.e. 0.33), 0.71 (s.e. 0.23) and 1.00 for fat dep th, muscle depth and live weight. Genetic correlations between male an d 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 la mbs (males only) with extensively reared females and males were 0.37 ( s.e. 0.22) and 0.67 (s.e. 0.17), respectively.