EFFECT OF THE BETA-ADRENERGIC AGONIST CIMATEROL AND DIETARY-PROTEIN LEVEL ON FAT YOUNG SHEEP GIVEN DIETS CONTAINING SUBMAINTENANCE LEVELS OF DIETARY ENERGY

Thirty Suffolk cross wether sheep aged about 12 months and weighing 57 kg on average were used. They had been given previously a high energy diet to produce a fat body condition and average condition score of 3 .7. Animals were allocated to an initial slaughter group (IS) or to fo ur dietary treatment groups (UL, LIH, CL and CH) based on sugar-beet f eed (L) or white-fish meal (H) supplemented with chopped straw and pel leted, without (UL and LIH) or with (CL and CH) the beta-adrenergic ag onist cimaterol, to provide an estimated 20 g (L) or 130 g (H) rumen u ndegradable protein per kg dry matter (DM). The sheep were offered 0.3 kg of the appropriate pelleted diet in addition to 200 to 400 g of ch opped barley straw to provide proportionately 0.7 of the estimated met abolizable energy requirement for maintenance and, where appropriate, 2.5 mg cimaterol per day. Comparisons were made for the main effects o f dietary protein intake and cimaterol and interactions between dietar y protein and cimaterol. The animals an dietary treatments were slaugh tered after 49 days. The animals exhibited variable reductions in live weight and weights of carcass and non-carcass components in compariso n with the IS group and in response to restricted dietary energy intak e. The only effect due to the elevated dietary protein provision was a smaller loss in live weight compared with the low protein diet. In co ntrast, compared with responses recorded in its absence, treatment wit h cimaterol resulted in significantly greater values for weights of co ld carcass, cross-sectional area of m, longissimus dorsi and weights o f DM, crude protein and ash in the carcass with significantly smaller weights for raw fleece. In comparison with the IS group, significantly smaller changes due to cimaterol were recorded for the weights of car cass crude protein and ash. Cimaterol treatment significantly increase d the weight loss of fat in the carcass and in the perirenal and retro peritoneal, but not omental, depots as components of fleece-free non-c arcass fat which was also significantly reduced in total. Interactions suggested that losses in carcass weight and DM in the presence of cim aterol were less and gains in carcass protein and ash greater, on the high than on the low protein diet. The results suggest that under cond itions of energy undernutrition cimaterol may induce smaller losses or larger gains in carcass but not non-carcass, cuticle protein at the e xpense of fat depletion in carcass and non-carcass fat depots.