Effect of Immune Challenge on Different Genotypes: How Sick Do They Get?

Purdue University 1999 Swine Research Report. There is a significant economic incentive for pork producers to increase the efficiency of lean pork production. Environmental and disease stresses impose detrimental effects on food intake, lean muscle growth, and overall animal health. Even minimal immune challenges such as modified live vaccines may slow growth rate and feed intake. Furthermore, genetic lines of pigs selected for high rates of lean gain appear to be more susceptible to the detrimental effects of stress on animal performance (Frank et al., 1997). Thus it is important to identify genes which predispose animals to stress and disease, and to subsequently develop management strategies which minimize the impact of environmental and disease stressors on animal growth and well being. A gene that may be important in the regulation of feed intake and energy metabolism during disease stress is leptin. Leptin is a protein that is made by and secreted from fat cells (Pelleymounter et al., 1995; Halaas et al., 1995; Campfield et al., 1995; Houseknecht et al., 1996). Leptin works at the level of the brain to regulate food intake and energy expenditure in rodents and humans (Houseknecht et al., 1998). In rodents, an immune challenge causes leptin levels to rise, which sends a strong signal to the brain to stop eating and results in anorexia (Grunfeld et al., 1996; Sarraf et al., 1997). Pigs produce leptin (Bidwell et al., 1997), and it is possible that leptin concentrations change with stress or disease and may be important in regulating feed intake, growth rate and recovery from disease stress.