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

This study investigated the effects of flock, sex and let: shape scores (as sessed in the live animal) on the carcass yield, conformation and compositi on 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 t issue growth rate using an index of live weight and ultrasonic muscle and f at depths measured at 20 weeks of age. The second (Conformation pock) had r ecently been established by mating rams of extreme conformation selected fr om the UK Texel population with ewes in the Lean Index flock. Lambs were ev aluated at a mean age of 139 days at the end of an 12-zueek performance tes t in which they were reared indoors on a concentrate diet. Prior to slaught er, the lambs were assessed for conformation of the hind leg (leg shape sco re). Mean live weights and ultrasonic fat depths did not differ significant ly between flocks or leg shape scores brit ultrasonic muscle depths were hi ghest in the high leg shape score (27.9, 27.7 and 30.1 mm in low medium and high scores, s.e.d. 055). 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 differ ences in other tissue weights. Consequently, lean: bone ratio and lean prop ortions 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, medi um and low scores respectively, s.e.d. 0.30), shorter side length and highe r values for all muscularity traits. Lean tissue distribution in major join ts and individual muscles did not differ between flocks but the mean propor tion of total lean in the higher priced cuts was higher (553.1 v. 543.9 g/k g, s.e.d. 326) 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 dept hs (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 hi gher proportion of lean in the sine than females (665.2 v 638.9 g/kg) brit did not differ in lean proportion in the live weight, carcass conformation and muscularity scores. Females carried a higher proportion of total lean i n the higher priced cuts (555.6 v. 541.8 g/kg; P < 0.01) and in some indivi dual 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.