Plants have developed mechanical and chemical defense strategies that are effective against herbivores. Plants contain chemicals that are known as secondary metabolites (allelochemical) and these chemicals do not directly involve in organisms’ reproduction and growth, on the other hand, they affect survival, growth and behavior of species. These compounds usually take ecological tasks and plants use these compounds against diseases, parasites, and predators for interspecies competition. It is known through the observations on feeding of herbivorous insects that these compounds act as deterrent chemicals or they are toxic against them. Feeding is one of the most fundamental and the most important behaviors for herbivorous insects. Even though host plant preference of herbivores is partially depend on nutrients, this behavior greatly depends on secondary chemistry of plants. Effects of secondary compounds on herbivorous insects can be positive or negative.

Tannins are phenolic metabolites, which naturally produced by plants. They can defend plants against pathogen microorganisms and viruses. According to animal nutrition, tannins have both adverse and beneficial effects depending on animal species, physiological state of the animal, structure and concentration of the tannins. The objective of this study was to review the literature about tannins, their effects and usage of tannins in animal nutrition.