Effect of dietary black cumin seed (Nigella sativa) on performance, immune status, and serum metabolites of small ruminants: A meta-analysis

A growing number of publications are identified toward the use of black cumin seeds (Nigella sativa L) on small ruminant animals since many beneficial evidences have been reported in humans and animals. This study used a meta-analysis approach to quantify the effect of black cumin seeds (BCS) supplementation on the productive performance, nutrients utilization, and blood metabolites profile of small ruminant animals. Following the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) protocols, a total of 23 studies were aggregated in a database and were analyzed using mixed model methodology classifying the studies as random effects and levels of BCS as fixed effects in the models. Results found that interaction between BCS levels and animal species tended to be significant whereas increasing dietary BCS levels linearly increased average daily gain (ADG) (p < 0.01, R2 = 0.538) and dry matter intake in lambs (p < 0.01, R2 = 0.958) but had no effect on sheep. Nitrogen (N) intake, and N digested were found to be significantly increased (p < 0.01) as inclusion rates of BCS increased while organic matter (OM), crude protein (CP), and ether extract (EE) intakes tended to increased (p < 0.10). In addition to other immune responses, strong positive relationships were found on the increase of concentration of IgA (R2 = 0.922) and IgG (R2 = 0.939) (p < 0.05) in response to increasing BCS supplementation. To conclude, black cumin seeds can be used as a safe and beneficial feed supplement to promote the growth of small ruminant animals such as lambs, sheep, and goats. © 2021 Elsevier B.V.