Orange (Citrus sinensis) essential oil as feed additive for sheep: nutrient intake and apparent digestibility, nitrogen balance, and rumen fermentation characteristics.

Feed additives have been used in high-concentrate diets to modulate ruminal fermentation; however, information on the metabolic effects of orange essential oil (OEO) under this dietary condition remains limited. The study aimed to evaluate the effects of increasing levels of orange essential oil as a source of D-limonene on nutrient intake, apparent digestibility, nitrogen balance, and ruminal fermentation characteristics in sheep fed high-concentrate diets, compared with sodium monensin. Ten rumen-cannulated Dorper × Santa Inês wethers were assigned to a 5 × 5 Latin square design and fed diets containing 90% concentrate. Treatments consisted of four OEO inclusion levels (0, 100, 500, and 1000 mg/kg dry matter [DM]) and sodium monensin (25 mg/kg DM; M25). Nutrient intake, apparent digestibility, nitrogen balance, ruminal pH, and short-chain fatty acid (SCFA) concentrations were evaluated. The OEO inclusion did not affect overall nutrient intake (P > 0.05). However, intake of dry matter, organic matter, crude protein, neutral detergent fiber, non-fiber carbohydrates (NFC), and total digestible nutrients was higher for OEO treatments compared with M25 (P < 0.05). Apparent digestibility of NFC decreased at the highest OEO level (1000 mg/kg DM; P < 0.05), although values remained higher than those observed with M25. Digestibility of other nutrients, nitrogen balance, ruminal pH, and SCFA profiles were not affected by OEO inclusion (P > 0.05). Under the conditions of this study, orange essential oil did not improve nutrient digestibility, nitrogen balance, or ruminal fermentation in sheep fed high-concentrate diets, although high inclusion levels negatively affected NFC digestibility. These results contribute to understanding the metabolic effects of limonene-rich essential oils as alternatives to ionophores in intensive feeding systems.