Beneficial and adverse effects of medicinal plants as feed supplements in poultry nutrition: a review

Medicinal plants exhibit colossal impact on poultry industries by improving its performance and productivity. However, some of these plants show adverse influence too by decreasing egg production percentage, egg mass, and microbiota counts. Green tea, nettle, pennyroyal, yarrow, and alfalfa in the form of seed, powder, and extract had vast potentiality to improve immunity, reduce the growth of pathogenic microbes, and improve the viable counts of lactic acid bacteria. Lavender, Alfalfa, and Nettle powder were able to improve egg yolk color. Furthermore, ginger reduced fat content in meat and increased color intensity. Flax seed increased alpha linolenic acid content in tissue, and increased n-3 fatty acid content in breast as well as thigh tissue. Physiological assessment showed that green tea, lavender, nettle, pennyroyal, and yarrow improved poultry immunity. Lavender and nettle improved internal organ traits. Interestingly, the use of flaxseed improved quail egg hatchability. Plants metabolites, particularly carvacrol and thymol showed its pivotal role as natural growth promoters by affecting growth performances, nutrient bioavailability, and immunity of broiler chickens. Additionally, in recent years, micro-encapsulation or nano-encapsulation of plant extracts and its metabolites improved growth performances of broiler chickens, thereby suggested wide utilization of this technique as a potential alternative to antibiotic growth promoters in future. This review sheds a light on beneficial as well as no adverse effects of some of the direct-fed important medicinal plants and its metabolites in poultry nutrition in order to suggest its key role in future poultry enterprise.