Potential of graded doses of neem (Azadirachta indica) seed oil on ruminal fermentation characteristics, degradability, and methane formation in vitro

Neem (Azadirachta indica) belongs to Meliaceae family, represented mainly by trees, and widely cultivated and adapted in many tropical regions. The objective of this study was to evaluate the effect of increasing doses of neem seed oil (NSO) on ruminal methane (CH₄) formation, diet degradability, and fermentation characteristics after 24 h of in vitro incubation. Treatments were randomly designed to four doses of NSO supplemented to the basal diet (0, 20, 40, or 60 ml/kg DM). Increasing NSO dose resulted in a quadratic decrease (P < 0.05) in net gas (expressed as ml/g DM and ml/g TDOM) and CH₄ (expressed as ml/g TDNDF) production, while CH₄ (expressed as ml/g TDOM), acetate and propionate proportions decreased linearly confirming a dose-related effect. A quadratic increase in TDOM and linear increase (P = 0.023) in DNDF, NH₃-N concentrations, and total protozoal counts were observed. However, a linear increase (P = 0.009) was found in the ruminal butyrate proportion and partitioning factor as dietary NSO supplementation increased. In conclusion, dietary NSO supplementation mediated some desirable fermentation patterns, reducing ruminal NH₃-N concentration and CH₄ production with some adverse effects on fiber degradability. However, practical research under long-term conditions is required for further investigation.