Body tissue development in lambs of two genetic lines analysed by X-ray computer tomography

Growth and development of carcass lean (LEAN), carcass fat (FAT), BONE, subcutaneous fat (SFAT), intermuscular fat (IeFAT), non-carcass fat (NcFAT) and non-carcass visceral tissue (NcVT) were analysed by computer tomography (CT) in male lambs of a meat line (ML, n = 62) and a control line of sheep (CL, n = 29). The ML animals were of origin Norwegian white sheep (NWS) crossed with Texel and selected for lean weight since 2001, while the CL was NWS animals bred for an overall national breeding goal. CT images were recorded at 40 mm intervals throughout the animal at a mean age of 44 (CT1), 90 (CT2) and 118 (CT3) days. Weight of body tissues was estimated by CT in each animal for each scanning. Traits were analysed by mixed model including line, dam age, year, age at CT1 (covariate) and random effect of lamb and scan event (lamb). Average daily growth (g/day) was analysed by general linear model in SAS including fixed effects and their two-traits interactions and age at CT1 (covariate). ML lambs had a heavier weight of LEAN at CT1 (P < 0.05) and showed a tendency of more LEAN at CT2 and CT3 than the CL. LEAN:BONE was significant larger for the ML compared to CL at all scan events, while FAT, FAT% and LEAN:FAT were similar for the two lines for all scan events (P > 0.05). CL had a greater average daily growth between the second and third scan event than ML but this was largely a larger growth in fat depots.