Lipopolysaccharide-induced reductions in food intake do not decrease the efficiency of lysine and threonine utilization for protein accretion in chickens.

Exposure of animals to infectious agents induces immune responses that result in reductions in food consumption and weight gain. The effect of these changes on amino acid requirements and utilization remains unclear. Three assays were conducted with young chicks with Escherichia coli lipopolysaccharide (LPS) used to stimulate the immune system. An initial study was conducted to evaluate the effects of LPS on animal performance. In a daily or alternate day injection regimen for 9 d, chicks were given intraperitoneal injections of sterile saline containing 0, 100 or 400 microgram LPS. Administration of 100 or 400 microgram LPS daily, or every other day, decreased both weight gain and food consumption. In two subsequent growth assays, chicks were fed graded levels of lysine or threonine and injected with either 0 or 400 microgram LPS every other day to evaluate the effect of LPS administration on the efficiency of amino acid utilization. At the three lowest amino acid doses, whole-body protein accretion was a linear function of supplemental lysine or threonine intake, and slopes of the accretion curves were not altered by LPS administration. The dietary lysine concentration required to maximize protein accretion was unaffected by LPS, but the absolute lysine intake required to maximize chick performance was lower in LPS-injected chicks than in saline-injected chicks. These results show that LPS administration reduces weight gain, food intake, efficiency of food utilization and the absolute quantity of lysine required to maximize these criteria. However, LPS administration does not affect the efficiency of amino acid utilization, nor does it affect the concentration of dietary lysine required to maximize performance.