Abstract:
Proc. Aust. Sot. Arzim. Prod. 1994 Vol. 20 GROWTH AND DRESSING PERCENTAGE OF WELL AND AVERAGE MUSCLED ANGUS STEERS D. PERRYA and W.A. McKIERNAN B ANSW Agriculture, Trangie, N.S.W. 2823 BNSW Agriculture, Scone, N.S.W. 2337 The useful addition of a descriptor of muscling (muscle score or eye muscle area) to measures of weight and fat on the live animal and carcase has been reported (Perry et al. 1993a, 1993b) in variable and diverse populations. However it is not clear if these results apply in a less diverse population, such as within a breed. To investigate whether the relationship between muscle descriptors and dressing percentage holds within an homogeneous population, and if there is an association between muscularity and growth, we Drew out 71 Angus weaner steers from a commercial herd and from the 3 lines selected for growth rate a at Trangie. These steers were fed a pelleted diet (metabolizable energy 10.4 MJ/kg) for 90 or 65 days before slaughter. Individual feed intake and weekly liveweight were recorded. Gross efficiency was calculated as liveweight change from beginning to end of the feeding period, divided by total feed intake over this period Before slaughter the steers were weighed and given a live muscle score (where A is well muscled and E is poorly muscled, McKiernan 1990). After slaughter carcase weight, carcase muscle score, and fat depth and eye muscle area at the 12/13th rib were recorded. Table 1. Mean and sample standard deviation for daily weight gain (kg/day), dressing percentage and eye muscle area (cm2) for different live muscle scores (where A is well muscled and E is poorly muscled) Better muscled animals grew slightly faster than poorly muscled animals (P c 0.05) but there was no difference (P > 0.05) in the gross efficiency of this gain. Live muscle score (P c O.OS), eye muscle area (P < 0.001) and fat depth (P c 0.001) were significantly associated with dressing percentage. Unadjusted means are shown in Table 1. At the same liveweight and fat depth the partial correlation coefficient of eye muscle area with live muscle score was 0.35 and carcase muscle score 0.37. At the same liveweight, fat depth had a partial correlation of -0.07 with live muscle score, and -0.19 with carcase muscle score. This study found a small but positive relationship between muscling and dressing percentage within a sample of Angus steers, similar to that found in more diverse populations. It also suggests that there may be small benefits to be gained in growth rate with better muscled cattle. McKIERNAN, W.A. (1990). Proc. Aust. Assoc. Anim. Breed. Genet. 8: 447-50. PERRY, D., McKIERNAN, W.A. and YEATES, A.P. (1993a). Amt. J. Exp. Agric. 33: 275-81. PERRY, D., YEATES, A.P. and McKIERNAN, W.A. (1993b). Amt. J. Exp. Agric. 33: 825-30. 349