The effects of dietary crude protein level on rate, efficiency and composition of gain of growing beef bulls
Anderson, P.T.; Bergen, W.G.; Merkel, R.A.; Hawkins, D.R.
Journal of Animal Science 66(8): 1990-1996
ISSN/ISBN: 0021-8812 PMID: 3209507 DOI: 10.2527/jas1988.6681990x
Two experiments were conducted to evaluate the effects of dietary CP level on rate, efficiency and composition of gain of growing beef bulls. In Exp. 1, 59 bulls (333 .+-. 15.8 kg) were used. Eleven bulls were slaughtered on d 0 to provide an estimate of initial carcass composition (9-10-11 rib section chemical analyses), and remaining bulls were assigned to treatment diets containing 10, 12 or 14% dietary CP. Bulls fed the 10% CP diet grew slower (P < .05) than bulls fed the 12 or 14% CP diet, although dry matter intake and feed-to-gain ratio did not differ. Bulls fed the 12% CP diet had fatter cascasses (P < .05) than bulls fed the 10 or 14% CP diets and had greater daily fat accretion than bulls fed the 10% CP diet. In Exp. 2, 60 bulls (318 .+-. 9.0 kg) were used. Bulls were assigned to initial slaughter (n = 6) or to one of three dietary treatments, 10, 12 or 14% CP, and were slaughtered after feeding for 66, 136 or 202 d (n = 6 .cntdot. treatment-1 .cntdot. slaughter time-1). Bulls fed 10% CP diets had lower (P < .05) rates of carcass protein accretion during d 0 to 136 and d 0 to 202. Carcass fat gain was similar among treatments over the entire experiment, although bulls fed the 14% CP diet gained more fat during d 0 to 136 than bulls fed the other treatments. These data indicate that 10% dietary CP is not adequate to support maximal growth of young bulls and suggest that limiting CP may decrease fatness.