Limiting amino acids for growing goats fed a corn grain, soybean meal and maize stover based diet

Two experiments were conducted to determine limiting amino acids (AA) for growing goats fed a corn grain, soybean meal and maize stover based diet. In experiment 1, three 4-month-old Liuyang Black growing wether goats (10.0 ± 0.1 kg), fitted with ruminal, proximal duodenal and terminal ileal cannulae, were used to determine flows of AA into the duodenum and apparent intestinal AA digestibilities. These data were used to calculate amounts of essential amino acids (EAA) that should be infused into the duodenum to match the ideal AA pattern of muscle protein according to calculations, which suggested that 0.91, 0.77, 0.58, 0.52 and 0.44 g/d of lysine, methionine, leucine, arginine and threonine were required, respectively, to be supplemented to the duodenum. In experiment 2, four 4-month-old Liuyang Black growing wether goats (10.0 ± 0.5 kg) fitted with duodenal cannulae were used in a 4×4 Latin square design experiment, and the four treatments were continuous duodenal infusion of a mixture of methionine, lysine and leucine at 0.77, 0.91 and 0.58 g/d, respectively (3EAA, from experiment 1), or replacement of 0.21 of methionine (−0.19 g methionine), lysine (−0.52 g lysine) or leucine (−0.56 g leucine) respectively with isonitrogenous glutamate infusion from the 3EAA mixture. Replacement of methionine, lysine or leucine reduced methionine concentrations in plasma. The magnitude of the change was greatest for methionine, followed by lysine and leucine. A general lack of statistical significance between AA replacement and 3EAA group on almost all measurements, except for plasma methionine concentration, was probably due to the small number of goats used. Nevertheless, for growing goats fed a corn grain/soybean meal/maize stover diet, methionine was likely the first limiting amino acid, followed by lysine and leucine.