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The purposes of this study were to determine the effects of BW in growing lambs on rates of palmitate esterification (PE) and activity of glycerophosphate acyltransferase (GPAT) in subcutaneous and intermuscular adipose tissue in vitro and to determine the relationship between these in vitro measurements and carcass lipid accretion. At 37, 49, 60, and 71 kg of live weight, nine, nine, eight, and seven Columbia-Rambouillet-cross ewe lambs, respectively, were slaughtered and adipose tissue was dissected for glycerolipid biosynthesis assays. One-half of each carcass was boned, and carcass soft tissue lipid was measured. In both adipose tissues, PE and GPAT activity were highest at 37 kg (P = .0001); the greatest accumulation of carcass fat occurred between 37 and 49 kg (P = .0001). Differences in PE and GPAT were less well marked between 49-, 60-, and 71-kg lambs, but both were generally decreased with increased BW. Significant [R.sup.2] from regressions of mass and percentage of carcass fat on either PE, GPAT, or steady-state glycerolipid synthesis (GLS) were from .39 to .44 (PE), .40 to .58 (GPAT), .50 to .75 (GLS), and .60 to .77 (PE, GPAT, and GLS combined). Changes in PE, GPAT, and GLS with BW were consistent with changes in rates of carcass fat accretion, which indicated a close relationship between glycerolipid biosynthesis in vitro and lipid deposition in vivo in growing-finishing lambs.

Fourteen mature, ovariectomized, western-range ewes with an initial mean BW of 72 |+ or -~ 4.5 kg and mean condition score (CS) of 7.5 |+ or -~ .3 were used to evaluate the relationship between CS and body composition. Diets of chopped straw and alfalfa hay were formulated to provide either maintenance energy or less than maintenance energy (100 or 60% of ME) to induce changes in BW and CS. After 180 d, ewes were weighed, scored for body condition, and slaughtered. All carcass components, viscera, and organs were analyzed for lipid, DM, and ash, and protein was determined by difference. Body weight and CS values were related by regression analysis to percentage of composition and weights of carcass components, carcass, and empty body. Body weight and CS were highly correlated (r = .89) and analysis indicated that each increase in CS resulted in an increase of 5.1 kg of BW. Condition score accounted for more variation of percentage of lipid in the empty body (|R.sup.2~ = .95) and carcass (|R.sup.2~ = .90) than did BW (|R.sup.2~ = .84 and .80, respectively). In contrast, BW accounted for more of the variation in carcass weight (|R.sup.2~ = .97) and empty BW (|R.sup.2~ = .99). Inclusion of both BW and CS in regression models did not increase the variation accounted for with the single best predictor. With mature western-range ewes in this study, CS was highly related to carcass lipids and could be used to describe energy reserves available to ewes.