A GENETIC-ANALYSIS OF EARLY GROWTH AND ULTRASONIC MEASUREMENTS IN HILL SHEEP

Genetic parameters were estimated for early lamb growth and ultrasonic measurements taken on Scottish Blackface lambs reared under extensive conditions on two Scottish hill farms. Measurements were taken on approximately 2000 lambs born to unselected ewes, and sired by 32 rams previously selected for different predicted carcass lean content. Heritabilities for birth weight, marking weight (at approx. 6 weeks of age) and weaning weight (at 17 weeks) were 0.7 (s.e. 0.04), 0.02 (s.e. 0.03), and 0.14 (s.e. 0.05), respectively. Heritabilities for ultrasonic muscle and fat depths at weaning were 0.27 (s.e. 0.09) and 0.16 (s.e. 0.06), respectively. There was a strong maternal effect on weight which declined from birth with lamb age and was relatively unimportant for the ultrasonic measurements. The rearing environment of the lambs (hill pasture v. 'improved' (or 'inbye') pasture) was an important environmental effect on the heritability estimate for backfat thickness, with that for lambs reared on improved pasture being twice that of hill-reared lambs. The implications of the results from this work on genetic improvement of sheep in hill environments are discussed.