Characterization of Nigella sativa Meal (NSM) and the Effects on In Vitro Rumen Fermentation and Degradability

Nigella sativa meal (NSM) is a by-product of the oil extraction process with potential use as a functional feed ingredient in ruminant nutrition due to its rich bioactive compounds and nutrient content. Therefore, this replicated (n = 6) completely randomized design (CRD) study aimed to firstly characterize NSM for its the bioactive compounds by chromatography–mass spectrometry (GC–MS) and liquid chromatography–MS (LC–MS). The effects of its dietary inclusion at 0%, 5%, 7.5%, and 10% NSM on in vitro rumen fermentation, gas production, CH4 production, and rumen degradability were analyzed. Rumen fluid was collected orally from five sheep (body weight 20 ± 2 kg/head) and incubated with basal diets supplemented with pre-determined levels of NSM. The identified bioactive compounds identified included palmitic acid, oleic acid, linoleic acid, phenolic, flavonoid, thymoquinone, and saponin. The results showed that the dietary NSM supplementation in the diet significantly increased (p < 0.05) gas production at 18 and 48 h, NH3–N concentration, IVDMD (In vitro dry matter degradability), and IVOMD (In vitro organic matter degradability). However, there was no significant effect (p > 0.05) on gas production at 12 and 24 h, and CH4 production, pH, acetate, propionate, iso-butyrate, butyrate, iso-valerate, valerate, the acetate-to-propionate ratio (A:P), or total VFA concentration. Rumen fermentation was optimally modulated up to 10% without adverse effects on digestibility or CH4 production. In this context, NSM acted as a functional feed ingredient in vitro. Therefore, in vivo analyses are required to confirm the efficacy under practical feeding conditions.