THE INFLUENCE OF FEED ENERGY LEVEL ON GROWTH AND CARCASS TRAITS IN BULLS OF TWO BREED TYPES

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Abstract
A serial slaughter experiment is described using 48 yearling bulls: 24 Hereford crossbred (HX) and 24 Beef synthetic (SY). Twelve bulls of each breed type were fed a high-energy, mainly grain diet (Hi) and the other 12 a pelleted alfalfa diet (Lo). The two breed types showed similar growth rate and feed efficiency, yet at constant carcass weight (375.2 kg) the HX were fatter (44.2 vs. 37.2 kg) and had less muscle (110.3 vs. 116.8 kg) in the dissected side than the SY. The Hi diet resulted in greater growth rate (1.46 vs. 1.06 kg/day) and feed efficiency (9.5 vs. 12.7 kg/kg), in both breed types, than the Lo diet and resulted in a greater rate of fat thickness accumulation (P = 0.001). At constant carcass weight (375.2 kg), the Hi diet gave more fat (46.9 vs. 34.5 kg) and less msucle (109.0 vs. 118.0 kg) and bone (24.6 vs. 28.0 kg) in the dissected side than the Lo diet in both breed types. It is concluded that biological type and diet can be manipulated independently to produce optimum carcass grades at various carcass weights. Key words: Fatness, feed energy, growth, carcass, bulls, beef production