Meeting Abstract
The importance of specific macronutrients to immune processes is partly due to their ability to provide the building blocks of immunoproteins and fuel expensive immune responses. More recently we have begun to appreciate that macronutrient content of the diet also can affect immune processes through the gut microbiome. In this study, we conducted two experiments. The first explored whether birds exhibit shifts in the gut microbiome community and immune responses when fed isocaloric diets differing in macronutrient ratios, specifically lipids and proteins. We then designed an experiment to determine whether birds alter macronutrient intake when presented with an immune challenge. We found that macronutrient content of the diet changed the relative abundance of microbes, but not the diversity of microbes present in the gut. Despite changes in the gut microbiome, we did not find effects of diet on the physiological endpoints we measured, complement activity and corticosterone concentrations. However, birds given the choice of isocaloric diets high in either protein or lipids, then injected with an immune antigen (lipopolysaccharide; LPS), exhibited illness-induced anorexia that was macronutrient specific. Birds decreased intake of the protein rich diet, but maintained intake of the lipid rich diet. These results indicate that birds exhibit selective feeding when immune challenged, presumably because lipids provide a larger caloric gain than proteins, and proteins can benefit pathogen growth. Although we did not detect macronutrient-specific effects on complement activity, immune effects may still occur and could be more apparent with a more severe immune challenge.
