Increased responsiveness to intravenous lipopolysaccharide challenge in steers grazing endophyte-infected tall fescue compared with steers grazing endophyte-free tall fescue

Fescue toxicosis in cattle occurs as a result of consumption of ergot alkal oids in endophyte-infected (E+, Neotyphodium coenophialum) tall fescue (Fes tuca arundinacea). The condition is characterized by pyrexia, decreased wei ght gains, rough hair coats, and decreased calving rates. The objective of this experiment was to investigate whether steers grazing E+ fescue have al tered host response to lipopolysaccharide (endotoxin, LPS) challenge compar ed with steers grazing endophyte-free (E-) fescue. Angus steers (n = 8) had continuously grazed either E+ (n = 4) or E- (n = 4) tall fescue grass for 8 months prior to the experiment. The E+ steers had lower body weight, depr essed average daily gain, and decreased basal serum prolactin compared with the E- steers prior to LPS administration. Each steer received a single bo lus i.v. injection of LPS (0.2 mu g/kg body weight; Eschericha coli; 026:B6 ) dissolved in sterile saline, and blood was serially collected every 30 mi n for 4 h and at 24 h post LPS administration. LPS increased serum tumor ne crosis factor-alpha (TNF-alpha), cortisol, and haptoglobin but decreased pl asma glucose and IGF-I. Importantly, however, TNF-alpha, cortisol, and IGF- I responses to LPS were greater in E+ compared with E- steers. These result s indicated that animals grazing E+ fescue had altered integrated metabolic host response compared with animals grazing E- fescue. Potentially, combin ed exposure to E+ fescue and a bacterial LPS could have greater deleterious effects on the animal compared with exposure to only one of the two and wo uld likely lead to increased catabolism.