Amino acid requirements of South African Mutton Merino lambs 1. Duodenal and carcass essential amino acid profile

The essential amino acid (EAA) composition of the carcass and duodenal dige sta content of South African Mutton Merino ram lambs, fed a standard total mixed diet high in rumen degradable protein (RDP), was investigated. The st andard diet consisted (%) of 30 lucerne, 8 wheat straw, 56.25 maize meal, 3 .5 molasses, 1 urea, 0.5 salt and 0.75 ammonium chloride. The carcass essen tial amino acid composition (g AA/100 g crude protein) was as follows: 6.94 arginine; 2.61 histidine; 3.19 isoleucine; 7.19 leucine; 7.03 lysine; 2.08 methionine; 4.15 phenylalanine; 3.79 threonine and 4.28 valine. This compo sition can serve as an example of the ideal protein requirements for carcas s growth of South African Mutton Merino ram lambs fed a standard diet high in RDP. Relatively large differences occurred between the average essential amino acid concentrations of the standard diet and duodenal digesta, with the exception of histidine, leucine and threonine. Duodenal digesta contain ed significantly lower (p < 0.05) concentrations of arginine, histidine, me thionine and threonine and significantly higher (p < 0.05) concentrations o f leucine and phenylalanine when compared to the carcass. Chemical score in dicated that the duodenal digesta was first-limiting in histidine and secon d-limiting in threonine, followed by arginine and methionine for the carcas s growth of South African Mutton Merino lambs fed a standard diet. Isoleuci ne, leucine and phenylalanine appear to be in excess for the carcass growth of lambs.