Effects of dry fiber plus solubles and a carbohydrase complex on nutrient digestibility, ruminal fermentation, and performance of finishing cattle

Abstract Two experiments were conducted to evaluate the effects of dry fiber plus solubles (DFS) inclusion, carbohydrase complex (CC) supplementation, and their interaction on nutrient digestibility, rumen fermentation parameters, performance and carcass characteristics of feedlot cattle. In Experiment 1, thirty rumen-cannulated Nellore steers were housed in 30 individual, fully covered pens with concrete floors, each equipped with an individual feed bunk and water. Steers were blocked by initial body weight (BW = 264 ± 35.4 kg; standard deviation [SD]) and randomly assigned to 1 of 6 diets in a 2 × 3 factorial arrangement with inclusion of DFS (15 or 45% of diet dry matter [DM]) and CC levels (0, 75 or 100 mg/kg of diet DM). In Exp. 2, four hundred crossbred bulls (BW = 314 ± 40.2 kg; SD), were assigned to pens (n = 6 or 8 bulls/pen), and randomly assigned to receive the same 6 diets described in Exp. 1 (n = 10 pens/diet). The experiment lasted 123 d consisting of a 15 d adaptation (step-up) and 108 d in a finishing diet. In both studies, data were analyzed using PROC MIXED from SAS. Significance was declared at P < 0.05. In Exp. 1, the inclusion of 45% of DFS increased neutral detergent fiber (NDF), ether extract (EE) and ash intake (P < 0.05), with no effect on dry matter intake (DMI) and nutrient digestibility (P > 0.05). CC did not affect nutrient intake (P > 0.05), but increased EE digestibility (P = 0.02). There was DFS × CC interaction for crude protein (CP) digestibility (P < 0.05), which increased with doses of CC in the diet containing 45% DFS. There were no interactions (P > 0.05) between DFS and CC doses for rumen fermentation parameters. The inclusion of 45% DFS increased ruminal pH (P = 0.03), with no effect on rumen short-chain fatty acids (SCFA) profile (P > 0.05). The CC decreased rumen acetate (P = 0.02), increased propionate (P = 0.01), and, consequently, decreased acetate:propionate ratio (Ac:Prop ratio) (P = 0.01). In Exp. 2, there was no DFS and CC doses interaction (P > 0.05). The inclusion of 45% DFS in the diet increased average daily gain (ADG) (P = 0.02), feed efficiency (G:F) (P = 0.02), net energy for maintenance (NEm) (P = 0.03) and net energy for gain (NEg) (P = 0.04) and decreased the content of fecal starch (P < 0.0001) compared with the inclusion of 15%. CC did not affect the performance and carcass characteristics of feedlot cattle (P > 0.05). In conclusion, the higher inclusion of DFS improved animal performance, whereas the CC modified ruminal fermentation patterns by increasing the molar proportion of propionate, with no effects on performance.