Carcass characteristics of southdown rams from high and low backfat selection lines

Carcass characteristics of Southdown rams from lines selected for high or low backfat depths (assessed ultrasonically at Position Cover the longissimus dorsi muscle at the last rib) were compared. Rams were 15-18 months old and average carcass weight was 29.5 kg fot the High-line (n = 36) and Low-line (n = 42) groups. When adjusted by covariance to the same carcass weight, animals from the High-line had higher dressing-out percentages, lighter weights of several internal organs, and shorter carcasses. At a constant side weight, the High-line sides contained 18% more dissectible fat and significantly lighter weights of muscle and bone. However, muscle to bone ratio and muscularity in terms of muscle weight per unit length were greater for the High-line group. The High-line carcasses contained a greater proportion of their weight in the rack and loin cuts. The greater weights of four dissectible fat depots in the High-line carcasses were the result of larger rather than more adipocytes. The results show that selection on the basis of a single fat depth measurement resulted in significant differences in all measures of fatness, and also in several other carcass characteristics.