Abstract:
Domestic trade weight steers (149) were assessed visually for subcutaneous fat and then given a live muscle score based on the thickness and convexity of their shape relative to frame size, having adjusted for subcutaneous fat. After slaughter, carcasses were given visually assessed carcass muscle scores based on the same critera. Fat depths at the P8 site and 12-13th eye muscle area were measured. Half of each carcass was boned-out into primal joints with subcutaneous fat trimmed to 6 mm. The weights of these joints plus meat trim (85% visual lean) were added to obtain the weight of saleable meat. The weight of fat trimmed from the carcass, primal joints, and meat trimmings during the bone-out process was added to obtain weight of fat trim. The assessors did not give steers with a greater subcutaneous fat depth better muscle scores when scoring for muscle and intermuscular fat. There was a negative correlation between live muscle score and P8 fat depth (-0.37), and no significant correlation between carcass muscle score and P8 fat depth. The associations between muscle score and yield of saleable meat were investigated using multiple regression techniques, with fat depth and muscle score sequentially added after weight in the model. The coefficient of determination and the residual standard deviation were compared at each stage. For saleable meat yield (kg), liveweight and carcass weight were the main contributors to the variation explained by the models fitted. For saleable meat yield as a percentage of carcass weight, most of the variation accounted for by the models fitted was explained by fat depth, muscle score, and eye muscle area. When added after weight and fat depth in regression models, muscle score significantly increased the coefficient of determination in all cases, with an associated decrease in the residual standard deviation. The effect was strongest for percentage of saleable meat. At the same weight and fat depth, animals or carcasses with better muscle scores produced more saleable meat.