Effect of Nitrate Supplementation on Digestion, Rumen Fermentation, Plasma Metabolites, and Nitrogen Use in Sheep Fed a High‐Forage Diet

ABSTRACT Dietary nitrate (NO 3 − ) is an alternative non‐protein nitrogen (NPN) source and has mitigation effects on enteric methane emission in ruminants. This study investigated the effects of NO 3 − supplementation on rumen fermentation, nutrient digestibility, and nitrogen (N) utilization, focusing on urea‐N and amino acid metabolism in sheep fed a high‐forage diet. Six Suffolk wethers were assigned to a 2 × 2 crossover design conducted over two periods of 40 days each. Dietary treatments included supplementation with either urea (1.4% dry matter [DM]) or calcium nitrate tetrahydrate (5.8% DM). Each supplement contributed 32% of the daily crude protein supply (12% of DM). Intake, nutrient digestibility, N balance, ruminal volatile fatty acid (VFA) profiles, and plasma fluxes of urea‐N and phenylalanine were not affected by NO 3 − supplementation, with a trend ( p = 0.075) toward reduced DM digestibility. Ruminal ammonia‐N ( p = 0.004) and plasma urea‐N ( p < 0.001) concentrations were lower, whereas ruminal NO 3 − ‐N ( p = 0.045) and plasma glucose, triglycerides, and cholesterol concentrations were higher ( p < 0.001) with NO 3 − supplementation compared to urea. These results demonstrate that NO 3 − can substitute for urea as an NPN source without affecting intake, ruminal VFA profiles, and urea‐N production in sheep.