The composition, fat distribution and yield of carcass beef from steers and heifers when entire, spayed, pregnant or fitted with an intravaginal device

Abstract

An experiment at the Pastoral Research Institute, Hamilton, compared the carcass composition and yield of one group of 14 Hereford steers, and four groups of 14 heifers, either spayed, fitted with an intravaginal device, pregnant or entire. The animals were slaughtered at 18 or 22 months when average fat depths and carcass weights were 5.8 mm and 188.0 kg, or 7.5 mm and 219 kg, respectively. When compared at a constant carcass weight, the steers generally had heavier boneless primary cuts, with less fat than the heifers (P<0. 05). Steers also had less channel and kidney fat, subcutaneous fat, intra-muscular and inter-muscular fat and consequently less total fat than heifers (P<.05) . Differences between heifer groups were generally small and non-significant. When compared at the same age, differences between heifers and steers in carcass fatness were generally not significant (P>0. 05) but trends similar to those described above were apparent. Estimated yield of carcass beef (muscle plus saleable fat) was affected by sex, fat depth and level of fat specified in the carcass beef. When lean carcass beef (1 5% fat) was specified, steers yielded about 3.8% more than heifers at the same weight and fat depth, but when fatter carcass beef (20% fat) was specified, this difference was reduced to about 3.2%. Removal of channel and kidney fat from the carcass brought the yield of steer and heifer carcasses to within about 3.0% of each other.