Carcass composition, conformation and muscularity in Texel lambs of different breeding history, sex and leg shape score

Abstract

AbstractThis study investigated the effects of flock, sex and leg shape scores (assessed in the live animal) on the carcass yield, conformation and composition of purebred Texel lambs. Two flocks were managed in a common environment. The first (Lean Index flock) had a 6-year history of selection for lean tissue growth rate using an index of live weight and ultrasonic muscle and fat depths measured at 20 weeks of age. The second (Conformation flock) had recently been established by mating rams of extreme conformation selected from the UK Texel population with ewes in the Lean Index flock. Lambs were evaluated at a mean age of 139 days at the end of an 11-week performance test in which they were reared indoors on a concentrate diet. Prior to slaughter, the lambs were assessed for conformation of the hind leg (leg shape score). Mean live weights and ultrasonic fat depths did not differ significantly between flocks or leg shape scores but ultrasonic muscle depths were highest in the high leg shape score (27·9, 27·7 and 30·1 mm in low, medium and high scores, s.e.d. 0·55). At constant slaughter weight, the lean weight in the side was 0·4 kg higher in the Conformation flock and 0·3 kg higher in lambs of high v. low leg shape score (P < 0·001) with no significant differences in other tissue weights. Consequently, lean: bone ratio and lean proportions in both the live weight and carcass were higher in the Conformation flock and in lambs of high leg shape score. Lambs of high leg shape score had better carcass conformation scores (14·1, 12·9 and 11·9, for high, medium and low scores respectively, s.e.d. 0·30), shorter side length and higher values for all muscularity traits. Lean tissue distribution in major joints and individual muscles did not differ between flocks but the mean proportion of total lean in the higher priced cuts was higher (553·1 v. 543·9 g/kg, s.e.d. 3·26) for lambs of high v. low leg shape score. Males were 6·5 kg heavier than females at scanning (P < 0·001), had lower ultrasonic fat depths (2·8 v. 3·2 mm; P < 0·01) but did not differ in ultrasonic muscle depths. At equal slaughter age, males produced 1 kg more lean tissue and had a higher proportion of lean in the side than females (665·2 v. 638·9 g/kg) but did not differ in lean proportion in the live weight, carcass conformation and muscularity scores. Females carried a higher proportion of total lean in the higher priced cuts (555·6 v. 541·8 g/kg; P < 0·01) and in some individual muscles. It was concluded that there is important variation within the Texel breed in lean yield at constant live weight and that this is likely associated with differences between strain and conformation type.