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 digesta content of South African Mutton Merino ram lambs, fed a standard total mixed diet high in rumen degradable protein (RDP), was investigated. The standard 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 essential 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 composition can serve as an example of the ideal protein requirements for carcass 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 contained significantly lower (p < 0.05) concentrations of arginine, histidine, methionine and threonine and significantly higher (p < 0.05) concentrations of leucine and phenylalanine when compared to the carcass. Chemical score indicated that the duodenal digesta was first-limiting in histidine and second-limiting in threonine, followed by arginine and methionine for the carcass growth of South African Mutton Merino lambs fed a standard diet. Isoleucine, leucine and phenylalanine appear to be in excess for the carcass growth of lambs.