Cytokines dramatically alter metabolic function and are potent anorexic agents that result in reduced feed intake and nutrient deficiency. These complex and dynamic events are summarized in Figure 1. Levels of hormones such as insulin, glucagon and corticosterone are altered. Amino acids are partitioned away from growth in favor of antibody production. Energy is used to increase body temperature and metabolic rate is increased while locomotion is decreased.
More glucose is required for fuel and fat utilization is impaired.
Amino acids are deaminated to supply glucose resulting in higher nitrogen in blood and excreta. Blood iron and zinc are decreased while copper and fat levels are increased. The effect of all these changes on nutrient requirements is not easily predicable but has been examined by several investigators. Results in Figure 2 show that less methionine and cystine are retained in muscle during immune stress. This reduced muscle demand for amino acids is offset by a higher demand for antibody protein production.