Abstract:
Proc. Aust. Soc. Anim. Prod. Vol. 17 431 RUMEN PROTECTED AMINO ACIDS AS SUPPLEMENTS FOR GROWING STEERS OFFERED LOW QUALITY ROUGHAGE DIETS _ _ _ J.A. LINDSAY , J.F. KIDD , M.D. CERVONI and D.J. REID _ Mature dry season pastures in the dry tropics of northern Australia contain low levels of N. Supplements of urea can overcome part of the N deficiency and when cottonseed meal is also fed liveweight is further increased (Lindsay 1984). Both microbial protein and cottonseed meal may be lacking in the limiting amino acids such as methionine and lysine (Storm and Orskov 1984) which are necessary for optimum growth. Thus when cattle graze low quality pastures and are offered supplements of urea and cottonseed meal amino acid supplementation should alleviate any deficiencies and allow optimum growth. Seventy-two Bos indicus crossbred steers were randomly allocated to one of five treatments. There were,four replicates in four treatments and two replicates in the fifth, making 18 pens of four animals in total. The basal diet of native pasture hay contained 0.4% N and was offered ad libitum. The supplements fed were: 30 g N as urea and either 125 g, 250 g or 400 g/d of protected protein. The two lower levels were offered with and without a supplement of 12 g methionine plus 6 g of lysine. The protected protein was a mixture of formaldehyde cottonseed meal and meat and bone meal (3:l). The amino acids were rumen protected by a polymer coating (Eastman Chemical Company, USA). The supplements were fed daily during a 71 day period. Table 1. Mean liveweight gain and mean dry matter intake # Means with dissimilar postscripts are significantly different (P<O.O5). The addition of an amino acid supplement significantly increased LWG when 125 g/d protected protein was fed. The LWG of animals fed 250 g/d protected proteinwas significantly higher than similar animals fed 125 g/d protected protein. There was no difference between feeding 400 g/d protected protein and 250 g/d protected protein plus amino acids. Thus amino acids may be added to protected protein either to increase LWG at lower intakes of protected protein or to reduce the amount of protected protein required for a given LWG. LINDSAY, J.A. (1984). In Hennessy, D.W. 'Conditions determining the need for supplemental N in cattle at pasture'. Proc. Aust. Soc. Anim. Prod. x 15:104. STORM, E. and ORSKOV, R.R. (1984). Br. J. Nutr. S 52:613. 8 Queensland Dept Primary Industries, Swan's Lagoon, Millaroo, Qld, 4807
