Effects of decreasing roughage NDF in diets with high inclusion of DDGS on performance, feeding behavior, and ruminal parameters in Nellore bulls

Abstract

This study evaluated decreasing levels of roughage NDF (10, 7, and 4 % in DM) in DDGS-based finishing diets. In experiment 1, growth performance, feeding behavior, and carcass characteristics were evaluated on 18 Nellore bulls blocked by initial body weight (BW), with 6 replicates per treatment, in a complete randomized block design. In experiment 2, digestibility, feeding behavior, and ruminal fermentation were evaluated on 6 Zebu crossbred steers in two, 3 × 3 Latin square designs. Differences were considered significant at P < 0.05 and trends were declared at P < 0.10. In experiment 1, DMI increased quadratically with decreasing roughage NDF (rNDF) with the greatest DMI value achieved at 7.43 % rNDF (P<0.01). Average daily gain tended to respond quadratically, with the greatest estimated value occurring at 7.23 % rNDF (P<0.09). Similarly, hot carcass weight and final BW tended to respond quadratically (P<0.09). No effects of roughage NDF level were observed on carcass dressing percentage. Animals that received the lowest dietary rNDF selected for particles longer than 8 mm (P<0.05). Increasing roughage NDF levels in the diet tended to increase time spent ruminating (P<0.06). In experiment 2, a greater inclusion level of rNDF did not affect DMI, but linearly increased NDF intake (P<0.01) and tended to decrease DM digestibility (P<0.09). Ruminal pH remained, on average, above 6. Ruminal ammonia-nitrogen increased up to an inclusion level of 6.6 % rNDF and then decreased (P<0.02). Acetate: propionate ratio linearly decreased with increasing levels of dietary roughage NDF (P<0.02). Decreasing roughage NDF inclusion level in diets with high levels of corn DDGS is viable without compromising performance or increasing the risk of ruminal acidosis occurrence. Diets containing between 7.23 % and 7.43 % of roughage NDF are proposed to be suitable when corn DDGS-based diets are used to maximize intake and weight gain.