The word "yeast" comes from the Old English word gist - gyst, and from the Indo-European word "yes", which can mean foam or bubble. Yeast microbes are thought to be one of the earliest organisms discovered. Many species and strains of yeast used in horse nutrition have been recorded, but the most common are Saccharomyces cerevisiae and Saccharomyces boulardii. S. cerevisiae is rich in highly digestible proteins, vitamins (B6, thiamin, biotin, riboflavin, nicotinic acid and pantothenic acid), magnesium and zinc, but is poor in calcium content. Advantages of using yeast for horses: reducing the negative impact of concentrated feed with a high starch content, improving protein digestion, improving the availability of calcium and phosphorus, improving the nutritional value of low-quality hay, improving the athletic performance of horses, improving the quality of food in the feeding of pregnant mares and better growth of suckling foals. During an experiment in which pony horses participated, it was proven that horses fed with added yeast have a reduced production of acetate in the large intestine, and an increased digestion of dry matter. Furthermore, in a similar study in which the yeast Yea - Sacc® 1024 is used, it was concluded that the production of acetate increases in most food mixtures, while it does not in hayloft. By adding Yea – Sacc® 1024 to laminitic horses, it resulted in better forage degradability, while the increased amount of acetate increased the fibrolytic activity. Looking at it from the other side, the consumption of a large number of cereals can cause hypersensitivity to certain diseases such as colic, laminitis, etc. The results of the research showed that the quality of milk was higher in mares that were fed 20 g/day. In addition to the quality of milk, yeast has a good effect on the functioning of anaerobic bacteria and lactate utilizators. The only domestic factory of food mixtures for horses in Croatia is Kušić promet d.o.o. Sveti Ivan Zelina, which use live yeast cultures of S. Cerevisiae in their mixtures.