Effect of undigestible neutral detergent fiber concentration in finishing diets containing dry-rolled or steam-rolled barley for feedlot steers

This study evaluated the impact of grain processing method (dry- vs. steam-rolling) and diet uNDF concentration (low vs. high; 5.7% vs. 6.6% on DM basis by replacing silage with straw) in finishing diets on feed intake, feeding behavior, growth performance, ruminal pH, fermentation parameters, inflammatory stress responses, and carcass traits of 376 intact (initial body weight (BW) ± SD, 440 ± 33.6 kg), and 24 ruminally cannulated steers (initial BW ± SD, 474 ± 30.5 kg). Steers were housed in 32 pens with 4 pens of 30 steers, and 28 pens of 10 steers. Eight of the pens with 10 steers, and all of the pens with 30 steers were equipped with GrowSafe to record individual feed intake and feeding behavior. Three cannulated and 7 intact steers were housed in the smaller GrowSafe pens. Diets included (1) dry-rolled barley and barley silage; (2) dry-rolled barley and barley straw; (3) steam-rolled barley and barley silage; and (4) steam-rolled barley and barley straw, formulated to contain 89% barley-grain, 6% roughage and 5% vitamin and mineral supplement (DM basis). Interactions between the processing method and uNDF concentration were observed for maximum ruminal pH, and concentrations of blood glucose and lipopolysaccharide-binding proteins. Compared to dry-rolling, steam-rolling did not improve growth performance, ruminal pH, fermentation parameters, or liver abscess scores, but did increase longissimus muscle (LM) area (P = 0.01) and decrease the proportion of AAA carcasses (P = 0.01). Steam-rolled barley decreased (P = 0.04) glucose and increased (P = 0.01) blood concentrations of insulin and acute phase proteins. Increasing uNDF did not affect feed intake, growth, carcass traits, or liver abscess scores, but did increase (P = 0.01) bunk attendance, meal duration, and to a lesser extent meal intervals (P = 0.04) and eating rate (P = 0.01). Increased uNDF raised (P = 0.04) mean ruminal pH and reduced the duration of pH below 6.0, 5.8, and 5.2, and tended (P = 0.06) to increase the acetate to propionate ratio. The lack of growth response to dietary uNDF concentration could be due to the small differences in uNDF intake, or that uNDF concentration was sufficient to prevent digestive disturbances. Increasing dietary uNDF altered eating behavior and ruminal pH in a manner that could reduce the risk of clinical and subclinical ruminal acidosis.