Effects of intra-duodenal provison of limiting amino acids on serum concentrations of immunoglobulins and tissue concentrations of DNA and RNA in growing goats fed a maize stover-based diet

The study was conducted to investigate the effects of intra-duodenal infusion of methionine (Met), lysine (Lys) and leucine (Leu) on dry matter intake (DMI), serum concentrations of total protein (TP), IgA, IgG, IgM and PUN, as well as tissue DNA and RNA concentrations in growing goats. In Experiment 1, 3 Liuyang Black growing wether goats (10.0±0.1 kg) fitted with ruminal, proximal duodenal and terminal ileal fistulae were used to determine the optimal amounts of the limiting amino acids infused into the lumen of the duodenum on the basis of the intestinal digestibility of amino acids and the amino acid pattern in muscle protein. This experiment established the infusion amounts of Met, Lys and Leu to be 0.77 g/day, 0.91 g/day and 0.58 g/day, respectively. In Experiment 2, 12 Liuyang black growing wether goats (10.0±0.2 kg), cannulated in the duodenum, were randomly divided into four groups according to body weights. The four treatment groups were the 21% removal of Met, Lys or Leu from the mixed Met, Lys and Leu solution, and a control group (full amounts of Met, Lys and Leu). Blood samples were taken from the jugular vein on day 8 before slaughter to measure changes in serum total protein (TP), IgA, IgG, IgM and plasma urea nitrogen (PUN), as well as DNA and RNA in skeletal muscle and jejunal mucosa. Serum TP and IgA were unaffected (P > 0.05) by the 21% removal of Met, Lys or Leu, compared with the control group. Serum IgG and IgM concentrations were lower (P < 0.05) in response to the 21% removal of Met or Lys, but PUN concentration were higher (P < 0.05) in response to the 21% Met removal, in comparison with the control group. Concentrations of DNA and RNA in both skeletal muscle and jejunal mucosa decreased in response to the 21% removal of Met and Lys, compared with the control group. Collectively, results indicate that the extent, to which the immune response and tissue protein-synthetic capacity are affected by the intestinal removal of essential amino acids, appear to be related to the order of their limitation in the lumen of the duodenum. © 2006 Elsevier B.V. All rights reserved.