Effect of castration and dietary protein level on growth and carcass composition in beef cattle

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Abstract
SUMMARY: Thirty-six Hereford cross Friesian calves weighing on average 82.4 kg at an average age of 90 days were allotted in randomized blocks to a 2 x 3 factorial design. Castration by the open method was performed on half the number of calves and three dietary crude protein levels, 20, 14 and 11 % in dry matter were used in a mainly cereal concentrate diet fed ad libitum individually to the animals in stalls. Slaughter was at a fixed weight of approximately 420 kg.Steers compared with bulls gained weight at a significantly slower rate and with less efficiency. Castration's greatest effect in reducing rate of gain occurred during the later stages of rearing when puberty in the bulls, as measured by a steep rise in seminal fructose, was associated with their relatively well maintained live-weight gain. The influence of testicular hormones was also apparent in the bull's carcass with its heavier head, horn and hide and significantly higher proportion of lean and lower proportion of fat in the side.Dietary protein level affected rate of gain in both bulls and steers but at each level bulls performed better than steers. With circumstances similar to those in this experiment, a 14 % crude protein level in concentrate dry matter appears adequate for both categories up to a live weight of circa 270 kg and a reduction to 11 % thereafter. The effect of protein level on tissue proportions of the side and carcass composition generally was minimal.