Dried yeast (Saccharomyces cerevisae) as a protein source for horses

The objective of this study was to evaluate the use of dried yeast in the diet of foals when replacing soybean meal to provide 0, 0.25, 0.50, 0.75 and 1.00 of the main protein source. Two trials were performed. Trial one was done to evaluate the influence of yeast on the digestibility of the five diets. Ten foals were kept in metabolic cages and five diets were tested twice. The experiment was repeated a second time, with foals receiving a different diet so that every diet was tested 4 times on a different animal. The concentrate was offered in a level of 2% of the body weight and Chloris guaiana hay was offered as roughage in a level of 1% of the body weight. In a second trial thirty 'Brasileiro de Hipismo' foals, aged between 12 and 14 months, were used. They were kept on pastures of Cynodon dactylon c.v. Coastcross and Cynodon spp. c.v. Tifton 85, and the concentrate was offered twice a day in separate pens at a level of 2% of the body weight. The pastures were of good quality and the pasture availability was high. The experimental design was a 5 × 3 factorial (five levels of yeast and three groups of animals in different pastures), with two replicates/treatment. The foals were weighed and measured every 28 days. Blood samples were collected at the end of the trial. The concentrate intake was measured daily. The pasture intake was measured through estimation of faecal output with chromic oxide and by the amount of acid detergent insoluble ash in the pasture, feed and faecal samples. The mean digestibility of dry matter, organic matter, crude energy and acid detergent fibre did not differ between the diets. A quadratic effect was observed for the digestibility of crude protein and neutral detergent fibre. Increasing the level of yeast in the diets did not have an influence on the average daily weight gain, heart girth gain, withers height gain, but linearly depressed the daily intake of the concentrate. However, the intake of pasture was not influenced by the different diets. The biochemical blood parameters total protein, albumin, globulin, urea, uric acid, creatinine, cholesterol, triglycerides, aspartate aminotransferase and gamma glutamyltransferase were not affected by increasing levels of dried yeast. It was concluded that dried yeast can be used as the only main protein source in the concentrate diets of 12 month old foals.