Gastrointestinal endotoxin and metabolic responses in cows fed and recovered from two different grain-rich challenges

Effects of two grain-rich feeding challenges and their subsequent recovery on gastrointestinal endotoxin concentrations, acute phase response, and blood metabolites were determined in eight rumen-cannulated, non lactating Holstein cows. A 2 x 2 cross-over design was used. At the start of the experiment, cows were fed forage-only diet (baseline, d 0) and after a 6-d gradual adaptation, challenged with a 60% grain diet for 4 wk (d 7 - 35), either continuously (CONT) or interruptedly with a 1-wk break in the second wk (INT). Subsequently, cows were fed the forage-only diet for 9 wk to evaluate the recovery of the grain challenges. Feeding challenges markedly increased ruminal and fecal endotoxin concentrations, which returned to the baseline levels during the recovery phase. Ruminal endotoxin concentration tended to be higher in CONT than in INT cows on d 14 and 25. The concentration of acute phase proteins serum amyloid A and haptoglobin were not affected by the feeding challenges. The level of the liver enzyme aspartate aminotransferase was transiently increased on d 14 and 25 only in the CONT cows. The concentration of glutamate dehydrogenase peaked on d 14 of both challenge models and lowered thereafter. Blood glucose and urea concentrations rose due to the challenges with glucose tending to be higher in INT than in CONT cows. Both feeding challenges lowered blood cholesterol, non-esterified fatty acids, and creatinine concentrations. In conclusion, the feeding challenges promoted endotoxin release in the rumen and hindgut but did not trigger an acute phase response. All altered variables returned to baseline values within 2 wk after the both interruptedly and continuously high-grain feeding.