The role of clove essential oil and condensed tannin supplementation in enhancing nutrient digestibility, rumen fermentation, blood metabolites, milk production, and the fatty acid profile in dairy goats

This experiment investigated the effects of clove essential oil (CEO) and a commercial condensed tannin (CT) on digestibility, rumen fermentation, blood metabolites, milk yield, milk composition, and fatty acid profile in lactating goats. Nine multiparous goats were used in a triplicated 3 × 3 Latin square design over three 21-d periods, with 14 d for diet adaptation and 7 d for data and sample collection. Goats were fed a basal diet without supplementation (CON), supplemented with CEO at 2 g/goat/d (CEO diet), or with CT at 2% of CT on a dry matter (DM) basis (CT diet). Digestibility of DM, organic matter, crude protein, and neutral detergent fibre was higher (p < 0.05) with the CEO diet than with the CON and CT diets. Total volatile fatty acid concentration and acetate proportion were increased (p < 0.05) in the CEO diet compared to the CT and CON diets. Both the CEO and CT diets lowered (p < 0.05) ruminal ammonia-N concentration and rumen methane production per kg DM compared with the CON diet. Blood urea concentration decreased (p = 0.02) on the CEO and CT diets versus the CON diet. Daily milk yield and the yields of fat-corrected milk, fat, protein, lactose, non-fat solids, and milk fat concentration were higher (p < 0.05) with the CEO diet than with the CT and CON diets. Polyunsaturated fatty acids (PUFA) increased (p < 0.01) while saturated fatty acids (SFA) decreased (p = 0.001) in the CON and CT diets compared with the CON diet. The CEO diet further increased monounsaturated fatty acids (MUFA) (p = 0.01) and improved the SFA/MUFA ratio (p < 0.01) compared to the CON diet. The proportion of C18: 0 (stearic acid) increased (p = 0.05) in the CEO diet compared with the CT and CON diets. In addition, C18: 1 n-9c (oleic acid) increased (p < 0.01) most in the CEO diet, followed by the CT diet, and then the CON diet. Compared with the CON diet, the proportions of C18: 2 n-6c (linoleic acid) and C18: 2 trans (TT) also increased (p < 0.05) in both the CT and CEO diets. In conclusion, both additives successfully mitigated environmental impacts by suppressing ruminal methane emissions and ammonia-N concentration. However, CEO demonstrated clear superiority over CT by simultaneously enhancing nutrient digestibility, increasing milk and component yields, and optimising the milk fat profile by reducing SFA while increasing MUFA and oleic acid content.