Abstract:
Proc. Aust. Soc. Anim. Prod. Vol. 18 CARCASS COMPOSITION OF CROSSBRED LAMBS SIRED BY TWO SIRE BREEDS D.L. HOPKINS* and A.A. BROOKS* It has been suggested that the Wiltshire Horn could fill a niche in Tasmania as a means to control ragwort because of its apparent capacity to graze the weed without deleterious effects. Even though there have been claims that the breed shows high growth rates (Hutching 1984) there is a dearth of carcass data available primarily because only small numbers exist in Australia. As part of a larger study (Hopkins 1988) the composition of 64 lamb carcasses was obtained, half being sired by two Wiltshire Horn (WH) and the remainder by four Poll Dorset (PD) rams. Groups were balanced for sex (ewes vs wethers). At slaughter the two groups of lambs were 220 days of age on average at which time hot carcass weight (excluding kidneys, kidney and channel fat) was recorded along with the hot GR (total tissue thickness at the 12th rib 110 mm from the midline). Percentage dissectable carcass fat and lean was determined. Poll Dorset sired lambs had a mean (2 8-e.) GR measurement of 12.5 + 1.00 mm which was not significantly greater than the WH lambs at 11.9 + 0.81 mm. Mean carcass weights were not significantly different at 17.4 + 0.65 and 15.7 + 0.56 kg respectively. Models were developed to predict carcass fat and lean percentage for each sire group using the independent variable GR. Sex and hot carcass weight had no significant bearing on the models. The models for carcass fat percentage were not significantly different between sire groups but were for lean percentage. The predicted values of lean percentage for WH sired lambs using GR measurements of 10 and 15 mm were 29.6 and 33.6% respectively and for the PD sired lambs 28.0 and 32.9% respectively. The results suggest that PD sired lambs may reach target carcass weights before WH sired lambs. Napier et al. (1980) found Suffolk and Hampshire Down sired lambs grew faster than WH sired lambs. There was some indication from their work however, that WH carcasses contained more lean tissue than Hampshire Down carcasses. Data presented here show the same trend. Interpretation of results is difficult as only a small number of rams were used in this study and in all previous work. In this sense it is impossible to be definite about the characteristics of the breed. HOPKINS, D-L. (1988). Proc. 34th Int. Congress of Meat Science and Tech. 78, HUTCHING, G. (1984). N.Z. 3. Agric. 149 (2):26. NAPIER, K-M., JONES, L-P. and WARD, R-G. (1980). Proc. Aust. Soc. Anim. Prod. 13: 421. * Department of Primary Industry, P-0, 180, Kingsmeadows, Tas. 7249. 494