44
Amino Acid Nutrition and Immunophysiology
Immune activation and the acute-phase response following infection produces a coordinated reduction in feed intake and growth performance in livestock species. As such, whole-body protein metabolism is altered to repartition amino acids away from synthesis of skeletal muscle protein and toward the production of specialized immune cells and proteins. In addition to the non-specific symptoms associated with infection, normal gastrointestinal function may be compromised due to decreases in nutrient digestion and absorption, especially if the animal is exposed to an enteric pathogen. From a nutritional perspective, these circumstances are quite challenging to manage because not only do sick animals consume less feed, but they experience shifts in amino acid metabolism, which are expensive from a livestock production standpoint. Therefore, it will become increasingly important to develop dietary strategies that can potentially prevent or alleviate performance losses during and after an infective period. In broiler chickens, coccidiosis is an economically-important disease resulting from infection of any one of nine Eimeria protozoan parasitic species. Our laboratory has recently focused on how acute immune activation due to Eimeria infection influences metabolic priorities of amino acids for the bird during and after infection. Key outcomes measured in this research include growth performance, markers of skeletal muscle protein breakdown, plasma carotenoid and proinflammatory cytokine concentrations, and ileal amino acid digestibility coefficients. We hypothesize that aligning the dietary amino acid profile with the composition of acute-phase proteins synthesized during an acute Eimeria infection will minimize growth performance deficits. Perhaps owing to the mismatch between amino acid compositions of skeletal muscle and acute-phase proteins, early evidence suggests dietary supplementation of phenylalanine, tyrosine, tryptophan, and serine can improve growth performance of birds during an acute coccidiosis infection, even when serum α-1-acid glycoprotein, an important acute-phase protein, remains elevated. Finding ways to manage the magnitude and duration of an acute inflammatory response is key to maximizing productive performance and profitability, and progress may occur by focusing on the post-infection (i.e., compensatory gain) period with regard to dietary amino acid strategies.
Keywords: amino acids, chicken, immunology