In-vivo composition of carcass regions in lambs of two genetic lines, and selection of CT positions for estimation of each region

Abstract

Data on 155 lambs computer tomography (CT) scanned at a mean age of 118 days and 41.5 kg were included in this study. The object was to examine in vivo composition in three major carcass regions, the leg, the mid-region and the shoulder of lambs of two genetic lines, a meat line (ML) and a control line (CL). Additionally, the study aimed to determine the best scan positions for estimating tissue weights in each region. Images were taken at 40 mm intervals, on average 23 scans per animal. Each CT scan was located to an anatomical position and to one of the three regions. Weight of lean, fat and bone was found for each region from all images located to a region. Tissue weights, and proportion of lean, fat and bone relative to the total weight of the region, was found by GLM adjusted for fixed effects and live weight (covariate). Stepwise regression procedure was used to find the best combination of scan sites for estimation of composition in each region. The ML had a significantly heavier weight and larger proportion of lean, and a lower proportion of bone in all regions compared to the CL. Furthermore, the ML had a lower proportion of fat in the leg and the mid-region than the CL ( P < 0.05). Moreover, the ML had a larger weight of lean in the leg than in the shoulder compared to CL ( P < 0.05). The latter indicated that selection for lean and introduction of Texel into the ML had increased the development of lean in the leg compared to the shoulder. Both lines had largest percentage lean (78–80%) in the leg and lowest in the shoulder (70–72%), whereas smallest percentage fat was found in the leg. A minimum of two scan sites should be recorded for estimations of the shoulder and the mid-region, and three for the leg. The best combination of scan positions for the shoulder was the 6th thoracic and the 7th cervical vertebra, for the mid-region the 4th lumbar and the 8th thoracic vertebra, and for the leg the 3rd and 4th caudal and the 4th sacral vertebra. Using these scan sites for estimation of tissue weights in each region, the R 2 ranged from 0.894 to 0.978 for lean and fat and from 0.689 to 0.833 for bone.