Backgrounding and finishing diets are associated with inflammatory responses in feedlot steers.

The objective of this investigation was to study the effects of feeding backgrounding and finishing diets on selected acute phase proteins in the plasma of feedlot steers. Two groups of 12 steers each, at the backgrounding and finishing stages, were offered either a backgrounding (45% barley grain-based concentrate and 55% barley silage on a DM basis) or a finishing (91% barley grain-based concentrate and 9% barley silage) diet for 12 and 15 wk, respectively. Steers at the backgrounding and finishing stages had initial BW of approximately 250 and 380 kg, respectively, at the beginning of the experiment. Blood samples were obtained from a jugular vein at 3-wk intervals during the experimental period beginning at wk 3 or 0 for the backgrounding and finishing periods, respectively. Plasma samples were analyzed for serum amyloid A (SAA), lipopolysaccharide-binding protein (LBP), haptoglobin, and alpha(1)-acid glycoprotein. Steers fed the finishing diet showed peak plasma SAA, LBP, and haptoglobin within 3 wk from the initiation of the diet (20, 23, and 1,940 microg/mL for SAA, LBP, and haptoglobin, respectively). Although plasma alpha(1)-acid glycoprotein reached a peak concentration (449 microg/mL) at the beginning of the finishing phase, no diet effect was obtained for this variable. Steers fed the backgrounding diet showed less variation in the concentrations of plasma acute phase proteins measured; plasma haptoglobin reached a peak concentration (1,720 microg/mL) 9 wk after the beginning of this diet. In conclusion, feeding feedlot steers the backgrounding or finishing diet was associated with increased peak concentrations of acute phase proteins in the plasma. More research is warranted to elucidate the mechanisms behind the inflammatory responses observed in feedlot steers and their implications for health issues and the production efficiency of feedlot operations.