Effects of Feeding Dry or Modified Wet Distillers Grains with Solubles with or without Supplemental Calcium Oxide on Ruminal Metabolism and Microbial Enzymatic Activity in Beef Cattle

Abstract Text: Objectives were to determine the interaction of feeding dry (DDGS) or modified wet (MDGS) distillers grains with solubles with or without supplemental CaO on apparent DM and NDF digestibility; in situ DM and NDF disappearance; ruminal pH, VFA, and methane concentrations; and cellulase and xylanase activity. Fistulated steers (n = 8; initial BW = 540 ± 250 kg) were used in a replicated 4 × 4 Latin square design. Treatments were arranged in a 2 × 2 factorial and steers were randomly allotted to 1 of 4 dietary treatments: (1) 50% DDGS with 0% CaO, (2) 48.8% DDGS supplemented with 1.2% CaO, (3) 50% MDGS with 0% CaO, or (4) 48.8% MDGS supplemented with 1.2% CaO. The remainder of the diets were husklage, dry rolled corn, and vitamin and mineral supplement. There were no interactions (P ≥ 0.12) of distillers grains (DGS) type and CaO supplementation on any variables; therefore, main effects are presented. Steers fed DDGS increased (P < 0.01) DMI by 17% when compared to steers fed MDGS; however, CaO supplementation reduced (P = 0.03) DMI. Supplemental CaO elevated (P < 0.01) dietary pH by 1.82 pH units. This caused a time post-feeding by CaO addition interaction (P = 0.05) for ruminal pH. Steers supplemented with CaO tended (P = 0.09) to have elevated ruminal pH at 1.5 h and had elevated (P = 0.03) ruminal pH at 3 h post-feeding; however, ruminal pH did not differ (P ≥ 0.24) the remainder of the day. There was no difference (P = 0.46) in ruminal cellulase activity when comparing type of DGS fed. There was a time by CaO supplementation interaction (P < 0.01). Cattle fed 1.2% supplemental CaO had greater (P = 0.02) ruminal cellulase activity than cattle fed 0% CaO only at 0 h post-feeding. Furthermore, feeding supplemental CaO increased (P = 0.04) the acetate to propionate ratio, but did not affect (P ≥ 0.07) other VFA concentrations. Supplemental CaO did not increase (P ≥ 0.48) in situ NDF disappearance or apparent NDF digestibility. However, cattle fed MDGS had increased (P < 0.01) NDF digestibility. There were no differences (P ≥ 0.48) in ruminal methane concentration when comparing DGS type or supplemental CaO. In conclusion, despite the fact that CaO increased ruminal pH and cellulase activity at certain times, it did not increase fiber digestibility in this study.

Keywords: beef cattle, calcium oxide, distillers grains, rumen metabolism