Relationship of Inflammatory Cytokines, Growth Hormone, and Insulin-Like Growth Factor-I to Reduced Performance During Infectious Disease

AbstractProduction of inflammatory cytokines and concentrations of growth hormone and insulin-like growth factor-I (IGF-I) were studied during experimental Escherichia coli mastitis to determine their potential involvement in reduced animal performance during infectious disease. During the first 10 to 14 hr after intramammary infusion of E. coli, bacteria multiplied to maximum levels of 104-109 cfu/ml of milk with no clinical signs of mastitis. A rapid and intense inflammatory response, characterized by udder swelling, increased bovine serum albumin (BSA) and somatic cell count (SCC) in milk of infected glands, and elevated rectal temperature and serum cortisol concentration, began at approximately 12 hr after challenge. Lactational performance was reduced greatly at 24 hr, and the maximal decrease averaged 76% and 63% among infected and uninfected glands, respectively, of challenged cows; three cows became temporarily agalactic in all glands. By 6 days, all cows had nearly or completely eliminated the E....