A comparison of carcass chemical fat content and muscle distribution in Merino and crossbred rams and wethers from birth to 50 kg liveweight

Abstract

The chemical fat content of and distribution of 24 individual muscles in the carcasses of 120 ram and wether lambs of Merino and of Dorset Horn x (Border Leicester x Merino) breeding were studied between birth and 50 kg liveweight. Rams contained significantly less chemical fat than wethers (P < 0.01), this difference becoming more marked as slaughter weight increased. Crossbreds yielded significantly higher chemical fat than Merinos (P < 0.05) only at 50 kg liveweight. Nine of the 24 muscles studied showed significant differences in relative growth between genotypes and sexes, and in each case the muscles concerned were located in the pelvic and thoracic limbs. Changes in muscle-growth coefficients with increasing slaughter weight occurred mainly below 30 kg, and four of the 24 muscles studied significantly changed their growth pattern more than once and are classified as 'multiphasic'. We conclude that the genotypes and sexes studied do not differ in muscle distribution in an economically important way, but that they do show major variations in fat content and maturity type which fit them for different patterns of production.