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

Dietary nitrate (NO₃ ^-) is an alternative non-protein nitrogen (NPN) source and has mitigation effects on enteric methane emission in ruminants. This study investigated the effects of NO₃ ^- 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 NO₃ ^- 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 NO₃ ^--N (p = 0.045) and plasma glucose, triglycerides, and cholesterol concentrations were higher (p < 0.001) with NO₃ ^- supplementation compared to urea. These results demonstrate that NO₃ ^- can substitute for urea as an NPN source without affecting intake, ruminal VFA profiles, and urea-N production in sheep.