Effects of Replacing Cottonseed Meal with Corn Dried Distillers’ Grain on Ruminal Parameters, Performance, and Enteric Methane Emissions in Young Nellore Bulls Reared in Tropical Pastures

SIMPLE SUMMARY: Dried distillers’ grains (DDG), a co-product of ethanol production from corn, is gaining attention for its efficiency in ruminant nutrition, as it meets both the energy and protein demands of livestock and is less costly than the popular alternatives. The aim of this study was to evaluate the effect of replacing cottonseed meal with DDG at two levels (50 and 100%) on young Nellore bulls grazing Marandu grass in the rainy season, focusing on ruminal parameters, animal performance, and methane (CH(4)) emissions. When replacing 50% of cottonseed meal with DDG, animals presented higher intakes of dry matter, organic matter, forage, and digestible organic matter, compared to 100% DDG. Ruminal parameters, including pH, acetate, and acetate: propionate, were higher when animals received only mineral supplementation. Animals supplemented with concentrate (cottonseed meal and/or DDG) presented greater daily weight gain and final body weight than the animals consuming mineral supplementation. Replacing cottonseed meal with DDG does not cause great variations in ruminal parameters, animal performance, and enteric CH(4) emissions in grazing Nellore cattle during the rearing phase in the wet season. However, supplementation of 0.3% body weight with the concentrate can improve the productive performance of grazing animals. Both protein sources, DDG or cottonseed meal, can be used to intensify grazing beef cattle production. ABSTRACT: Two experiments were conducted to evaluate the effect of replacing cottonseed meal with DDG on ruminal parameters, methane (CH(4)) emissions (Experiment 1), and animal performance (Experiment 2) of young Nellore bulls grazing Marandu grass during the rainy season. Four supplementation strategies were used in both experiments: (1) Mineral supplementation (MS); (2) conventional multiple supplement (energy/protein) with cottonseed meal and citrus pulp (CMS); (3) CMS with 50% cottonseed meal replaced by DDG (50DDG); and (4) CMS with 100% cottonseed meal replaced by DDG (100DDG). The 50DDG condition resulted in greater intake of dry matter (p = 0.033), organic matter (OM) (p = 0.050), forage (p = 0.035), and digestible OM (p = 0.031) than 100DDG. The supplemented animals presented greater final body weight (BW) and average daily gain than the animals consuming MS (p = 0.011), and lower pH, acetate, and acetate:propionate (p < 0.05). However, the treatments had no influence on stocking rate, gain per area, and enteric CH(4) emissions (p > 0.05). Replacing cottonseed meal with DDG does not result in great variations in ruminal parameters, animal performance, and enteric CH(4) emissions of grazing Nellore cattle during the rearing phase in the wet season. Both protein sources in 0.3% BW supplementation can be used to intensify beef cattle production in pastures.