RELATIONSHIP OF INFLAMMATORY CYTOKINES, GROWTH-HORMONE, AND INSULIN-LIKE GROWTH-FACTOR-I TO REDUCED PERFORMANCE DURING INFECTIOUS-DISEASE

Production of inflammatory cytokines and concentrations of growth horm one and insulin-like growth factor-I (IGF-I) were studied during exper imental Escherichia coli mastitis to determine their potential involve ment in reduced animal performance during infectious disease. During t he first 10 to 14 hr after intramammary infusion of E, coli, bacteria multiplied to maximum levels of 10(4)-10(9) cfu/ml of milk with no cli nical signs of mastitis, A rapid and intense inflammatory response, ch aracterized by udder swelling, increased bovine serum albumin (BSA) an d somatic cell count (SCC) in milk of infected glands, and elevated re ctal temperature and serum cortisol concentration, began at approximat ely 12 hr after challenge, Lactational performance was reduced greatly at 24 hr, and the maximal decrease averaged 76% and 63% among infecte d and uninfected glands, respectively, of challenged cows; three cows became temporarily agalactic in all glands, By 6 days, all cows had ne arly or completely eliminated the E, coli, and milk production had par tially recovered, Milk composition showed an initial decrease in fat p ercentage followed by an increase thereafter, Protein percentage was i ncreased and lactose content was reduced during most of the mastitic e pisode, High concentrations of tumor necrosis factor (TNF) and interle ukin-l (IL-l) were detected in milk of infected glands, and their appe arance preceded or coincided with development of the mammary inflammat ion, systemic reaction, and hypogalactia. Serum growth hormone concent ration was higher among challenged cows, whereas serum IGF-I concentra tions changed little during the mastitic episode. Concentrations of IG F-I in milk whey increased from 5.0 to 12.2 ng/ml among infected gland s and from 4.4 to 8.5 ng/ml among contralateral, uninfected glands; IG F binding proteins also increased in the milk of infected glands, Thes e data demonstrate that (i) reduced lactational performance is not cau sed by reduced concentrations of growth hormone or IGF-I and (ii) infl ammatory cytokines are produced at a time consistent with a possible r ole in the inhibition of milk synthesis.