Nitrogen Supplementation Increases Feed Intake and Reduces Methane Yield in Steers Fed Low-Quality Weeping Lovegrass Hay

Feed intake and diet quality are key factors influencing enteric methane (CH4) emissions in ruminants. Low-quality C4 grasses typically limit intake and are associated with high CH4 yield. Nitrogen supplementation may improve rumen function and reduce CH4 emissions per unit of feed intake, although responses under low-quality forage conditions remain insufficiently characterized. The goal of the study was to evaluate the effects of nitrogen supplementation (urea- or nitrate-containing supplements) on the utilization of low-quality weeping lovegrass hay (Eragrostis curvula) and CH4 yield in beef steers. Twenty-four Aberdeen Angus steers (326 ± 27 kg body weight) were assigned to three treatments: (1) weeping lovegrass hay alone; (2) weeping lovegrass hay + sunflower expeller + urea; and (3) weeping lovegrass hay + sunflower expeller + potassium nitrate (KNO3). The proportion of non-protein nitrogen (NPN; urea and KNO3) included in the supplements was set according to the maximum tolerated threshold. Methane emissions were measured using the SF6 tracer technique. Compared with the hay-only treatment, supplemented animals increased dry matter intake (DMI) by 35% and 38% in the urea and nitrate treatments, respectively (p < 0.01). Total CH4 emissions (g/d) were not affected by treatment (p = 0.16). However, CH4 yield (g CH4/kg DMI) decreased by 27% and 38% in the urea and nitrate treatments, respectively (p < 0.01). The methane conversion factor (Ym) was also reduced in supplemented animals. Under the conditions of this study, supplementation of low-quality weeping lovegrass hay with nitrogen-containing supplements increased feed intake and reduced CH4 yield without affecting total CH4 emissions. These findings highlight the importance of considering CH4 emission intensity, in addition to absolute emissions, when evaluating mitigation opportunities in forage-based beef production systems.