330 - 3-nitrooxypropanol Supplementation of a Forage Diet Decreased Enteric Methane Emissions from Beef Cattle Without Affecting Apparent Total-tract Digestibility

Supplementation of ruminant diets with the investigational methane (CH₄) inhibitor 3-nitrooxypropanol (3-NOP; DSM Nutritional Products, Switzerland) is as a promising mitigation strategy. However, most studies have examined high grain or mixed forage-concentrate diets. The objective of this study was to evaluate the effects of supplementing a forage diet with 3-NOP on rumen fermentation, CH₄ emissions and apparent total-tract nutrient digestibility. Eight ruminally cannulated beef heifers (BW = 514 kg) were randomly allocated to two treatments in a crossover design with 49-d periods. Dietary treatments were: control, high-forage diet (90% forage DM basis) without 3-NOP; and NOP, control diet supplemented with 150 mg 3-NOP/kg DM. After a 14-d diet adaption, dry matter (DM) intake (DMI) was recorded daily. Rumen contents were collected on days 17 and 28 for volatile fatty acid (VFA) analysis, whereas ruminal pH was continuously monitored from day 20 to 27. Diet digestibility was measured on day 38 to 41 by total collection of feces. Enteric CH₄ emissions were measured on days 46 to 49 in chambers. Dry matter intake was lower (P = 0.001) for NOP (10.0 kg/d) as compared with control (10.2 kg/d). However, DM, neutral and acid detergent fiber, and crude protein digestibilities were similar between treatments (P ≥ 0.29). Although total VFA concentration was not affected by treatment (P = 0.19), the reduction in acetate and increase in propionate proportion for NOP lowered (P < 0.001) the acetate to propionate ratio by 18% as compared with control. Mean pH was lower (P = 0.03) for control (6.46) than NOP (6.57). Furthermore, CH₄ yield (g/kg DMI) was 21.6% less (P < 0.001) for NOP relative to control (25.5 g/kg DMI). Overall, the results indicate that enteric CH₄ emissions were effectively decreased with 3-NOP supplementation of a forage diet without affecting apparent total-tract digestibility of nutrients.