LAMB CARCASS CHARACTERISTICS .1. THE INFLUENCE OF CARCASS WEIGHT, FATNESS, AND SEX ON THE WEIGHT OF TRIM AND TRADITIONAL RETAIL CUTS

Carcass data were obtained for 258 lambs [hot carcass weight 16.0-28.7 kg, fat depth at the GR site (12th rib) 5-23 mm]. The sample included ewes, wethers, and cryptorchids (86 of each). Of these, 130 carcasses (42 ewes, 45 wethers, 43 cryptorchids) were prepared as boneless, heavily trimmed, 'trim lamb' cuts (i.e, a range of cuts promoted by the Australian Meat and Livestock Corporation). The remaining 128 carcasses (44 ewes, 41 wethers, 43 cryptorchids) were prepared as traditional, trimmed, bone-in cuts. Comparison of fat depth values before and after trimming over the loin at the 12th rib showed that the fat depth was reduced to a maximum of 4.0 mm. Models were developed based on hot carcass weight and GR measurement to enable estimation of the weight of each cut and carcass component (e.g. fat waste). The amount of variation of the components explained by the independent variables hot carcass weight and GR (R(2) values) ranged from 0.46 to 0.93. The time to prepare trim cuts from 115 carcasses and traditional cuts from 121 carcasses was measured. Depending on the combination of trim cuts prepared, it took a butcher, on average, 9.6-13.1 min longer to prepare these cuts from each carcass than to prepare traditional cuts, without considering the weight and fatness of the carcass. Regression analysis showed that preparation time increased as carcasses become either heavier or fatter, irrespective of the type of cuts being prepared. When differences in carcass type were accounted for, the difference in preparation time between trim lamb and traditional cuts decreased. The effect of fatness on preparation time was such that for every 5-mm increase in GR (equal to a fatscore), an additional 1-2 min was required to prepare both types of cuts. When the hindleg was broken down into trim cuts, the round cut from the cryptorchid carcasses was significantly heavier than from the ewe and wether carcasses. The neck and shank from cryptorchid carcasses were heavier (P<0.05) than from ewe and wether carcasses. Ewe and wether carcasses produced heavier (P<0.05) ribloin cuts (7- or 8-rib cut) than cryptorchid carcasses. There was a variable effect of sex on the cuts from the loin, with cryptorchid carcasses producing heavier (P<0.05) midloins but lighter (P<0.05) boneless loins than the ewe carcasses. There was no difference (P>0.05) between ewe and cryptorchid carcasses for the weight of the eye of loin, and there was no sex effect on the weight of the chump. Cryptorchid carcasses produced more (P<0.05) sausage trim than wethers, which produced more than ewes, this being a reflection of a decreasing proportion of breast and flap. Regardless of cutting method, cryptorchid carcasses produced significantly more saleable components than wether and ewe carcasses, which were similar. For a carcass of cold weight 20.2 kg and GR 12.5 mm prepared into one of the combination of trim cuts, the proportion of saleable meat is estimated to be 75.9, 73.4, and 73.7% for cryptorchids, wethers, and ewes.