Growth path affects the carcase composition of lambs

Abstract

Proc. Amt. Sot. Arzim. Prod. I994 Vol. 20 GROWTH PATH AFFECTS THE CARCASE COMPOSITION OF LAMBS R.S. HEGARTY, V.H. ODDY, R.L. SMITH and S.A. NEUTZE NSW Agriculture, Elizabeth Macarthur Agricultural Institute, Camden, N.S.W. 2570 The physiological processes regulating lamb ti orowth make it difficult to produce heavy lean lambs (carcase weight > 22 kg; fat score c 4) in current farmin g systems (McLaughlin 1992). Nutritional strategies, such as periods of restricted feedin g, modify body composition in lambs (Hodge and Star 1984) and may have application in producing heavy lean lambs. As part of an experiment evaluating nutritional strategies to promote lean growth, studies were made of the effect of a restricted feeding period and realimentation on the carcase composition of lambs. Wether lambs from a commercial property (n = 128; Border Leicester x Merino ewes, Poll Dorset sires) approximately 4 months of age with a mean liveweight (LW) of 28.1 kg were individually penned and fed according to a 2x4x4 factorial design. The 3 factors were as follows: (1) Intake level in the initial 18 week feeding period (maintenance at 35 kg LW (LO) or ad-libitum to 50 kg liveweight (HI). (2) Total level of intake (including rumen escape protein supplement; REP) in the final 12-15 week feeding period (0,500, 850, 1200 g as fed/day: 10 MJ ME and 123 g crude protein in dry matter of basal diet). (3) Level of REP supplementation in the final 12-15 week feeding period (0, 30, 60, 90 g formaldehyde-treated casein/day). A 4 week dietary adjustment period was allowed between initial and final feeding periods. Groups of lambs were slaughtered throughout the trial with 96 lambs being slaughtered at the conclusion of the experiment. All carcases and samples of non-carcase tissues were weighed and kept for protein, fat and ash analysis (Table 1). Table 1. Carcase weight and percentage of fat, protein and ash in the carcase of lambs fed to maintenance (LO) or fed ad-Zibitum (HI) for 18 weeks then finished on a range of intakes and levels of supplementary rumen escape protein (REP) before slaughter (REP effects not included) REP did not significantly affect of the experiment. Intake level in of fat (P c 0.001) and protein ( P c lambs contained less fat (P c 0.01) potential for restricted feeding and the percentage of protein, fat or ash in the carcase at the conclusion both the initial and final periods significantly affected the percentage 0.01) in the carcase. At the same carcase weight, carcases from LO and more protein (P c 0.1) than did those of HI lambs, indicating the realimentation to reduce fatness in lambs. HODGE, R.W. and STAR, M. (1984). Aust. J. Exp. Agric. Anim. Husb. 24: 150-5. MCLAUGHLIN, J.W. (1992). Proc. Aust. Sot. Anim. Prod. 19: 173-5. 360