Tannins are found in various feeds and can produce numerous benefits to ruminants, such as preventing bloat, favoring a better use of dietary protein, increasing microbial protein synthesis, according to its concentration, molecular weight and structure. The tannins affect the digestibility of the protein, because they form complexes with dietary proteins, improving the duodenal flow of proteins, of some essential amino acids and of unsaturated fatty acids, modifying the profile of two fatty acids of meat and milk and age in rumen biohydrogenation, They provide faster growth rates of live weight, higher milk production, increased fertility and reduction of the parasite load, improving the animal's well-being and health. The nutritional effects of two tannins may vary according to the type of tannin used and the level of inclusion in the diet, its chemical structure and molecular weight, the quantity ingested, the species or animal category involved and the energy and protein balance of the diet.