Plant-food by-products to improve farm-animal health

•Experiments on plant-food by-products to improve farm-animals health are reviewed.•Grape-pomace, grape-seed extracts and tamarind seeds stimulate beneficial bacteria.•Green tea and pomegranate by-products enhance the health status of farm animals.•Cottonseed meal improves the immunocompetence of farmed fish.

Livestock health is a worldwide issue because of the expected rise in meat demand in the coming years, with a consequent intensification of animal-production systems. As these systems extensively administer antibiotics, use is expected to increase sharply in the near future. Such use leads to resistance to these treatments, posing a serious threat to animal health throughout the world. This problem of farm-animal health can be alleviated by the use of natural alternatives, such as providing plant by-products as feed complements, which contain suitable concentrations of antimicrobial and health-promoting agents. This review describes and analyses the still limited research on the use of plant-food by-products to feed farm animals to bolster health. Future actions needed to improve knowledge for avoiding antibiotic resistance in animal rearing are also outlined. The by-products reviewed influence microbiological changes, reducing ileal coliform counts and improving small-intestinal indicator microbes, as well as having positive effects on the farm-animal immunology. Also, blood glucose, urea, creatinine, triglycerides, cholesterol, and cortisol concentrations usually decrease after the intake of plant-food by-products. Furthermore, some of these by-products cause significant up-regulation of several genes, while the antioxidant activity in muscle increase. Cottonseed meal, green tea, apple- and red-wine pomace have been the most thoroughly tested plant-food by-products.