Effects of Genotype, Environment, and Feeding Antibiotics on Serum Concentrations of IGF-I and a1-Acid Glycoprotein
Purdue University 1999 Swine Research Report. It has long been known that management practices such as genetic selection, all-in/all-out (AIAO), segregated early weaning (SEW), and feeding diets containing antimicrobials have the potential to increase the efficiency of lean pork production. However, the physiological reasons for this increase in efficiency have yet to be fully discovered. It is common knowledge that pigs subjected to pathogens and other stressors do not reach their genetic lean growth potential. Possible blood-borne markers for lean growth potential and immune system activation include insulin-like growth factor-I (IGF-I) and a1-acid glycoprotein (AGP). IGF-I is a protein produced by several tissues that mediates many of the effects of growth hormone, such as the stimulation of lean tissue growth and the prevention of lean tissue breakdown. Circulating levels of IGF-I are sensitive to the nutritional and energy status of the animal (Brameld et al., 1996; Weller et al., 1994). The serum concentrations of IGF-I also reflect the health status of an animal. Experimental data demonstrate that an acute phase response (fever, lethargy, anorexia) due to endotoxin injection and parasite infestation includes a sharp decrease in circulating IGF-I levels (Fan et al., 1995; Prickett et al., 1992). The feeding of diets containing subtherapeutic levels of antimicrobials to pigs has been shown to increase serum IGF-I concentrations, along with average daily gain and feed efficiency in young pigs (Hathaway et al., 1996). The results of these experiments suggest that if the pathogen and parasite load on animals is reduced through such practices as AIAO, SEW, and feeding antimicrobials, increased serum concentrations of IGF-I can be obtained and therefore more efficient lean tissue growth can be achieved. AGP is an acute phase protein produced by the liver in response to inflammatory stimuli. AGP has been demonstrated to work in a negative feedback manner upon the immune system, and works to reduce the inflammatory response (Elg et al., 1997). Attempts have been made to determine the health status of pigs through the measurement of serum AGP as well as other acute phase protein concentrations. Itoh et al. (1992) found that serum AGP levels were higher in pigs raised in a conventional herd than pigs raised in an SPF system.