Neem oil modulates rumen fermentation properties in a continuous cultures system

Neem oil is a commercialized product derived from fruits of the neem tree that has been shown to have antibacterial, antifungal and antiparasitic activities in various animal species. Our objective was to investigate effects of addition of neem oil to a feedlot finishing diet on rumen fermentation, ruminal digestibility and bacterial protein synthesis in a dual effluent continuous culture system. The experiment was designed as a replicated 3 × 3 Latin square with the treatments: control (no neem oil), low (20 g/kg of diet) and high (40 g/kg of diet, dry matter basis) amounts of neem oil. The experimental diet consisted of 872 g/kg of steam-rolled barley grain, 84 g/kg of whole crop barley silage and 44 g/kg of supplement (dry matter basis). Results indicate that concentrations of ruminal volatile fatty acid (VFA), as well as molar proportions of acetate and branch-chained FA, tended (P<0.10) to linearly decrease, whereas the proportion of butyrate tended (P<0.06) to be higher with increasing neem oil supplementation. Ruminal digestibilities of dry matter (0.79, 0.77 and 0.71), neutral detergent fibre (0.65, 0.64 and 0.56), starch (0.89, 0.85 and 0.82) and degradability of crude protein (0.78, 0.78 and 0.67) for control, low and high neem oil supplementation decreased linearly (P<0.01). The amount of bacterial N synthesized (g/day) tended (P=0.08) to increase linearly by 24% or 13%, respectively, for low and high neem oil supplementation compared with control. Bacterial N efficiency (g N/kg of ruminal truly fermented organic matter) was improved (linear: P<0.01) with neem oil supplementation. Results indicate that supplementation with neem oil supplementation inhibited ruminal microbial activity, possibly due to the bioactive compounds contained in neem oil. However, the lower ruminal digestibility of starch with low neem oil supplementation might be used to alleviate acidosis without having detrimental digestion of fibre and protein in feedlot cattle fed high-grain diets.