Live yeasts as a non-hormonal alternative to improve the performance of dairy cows

The present study aimed to evaluate live yeast dietary supply instead of rbST application in lactating dairy cows. Thirty-five Holstein cows (37.1 ± 7.8 kg/d of milk yield and 524 ± 27 kg of body weight; mean ± SD) were used in a completely random trial to evaluate: 1) rbST: animals treated with 500 mg of rbST every 14 d; and 2) Yeast: animals fed diets containing 40 g/d of live yeast. The trial lasted for five subsequent 14-d periods. Treatments showed no effects on cows’ feed intake. Yeast reduced large and small particles selection indexes compared, feed residue and starch in feces compared to rbST. Cows treated with rbST had increased glucose, triglycerides, and AST, and decreased cholesterol and urea serum concentration. In addition, yeast reduced somatic cells count and increased milk yield and cows’ production efficiency. Although treatments showed no effects on milk chemical composition, yeast increased saturated to unsaturated fatty acids ratio. Yeast increased saturated and short-chain fatty acids, whereas reduced unsaturated and cis-9 trans-11 C18:2 FA content in milk fat. Thus, yeast could be used instead of rbST to improve milk yield and the productive efficiency of cows in a short-term evaluation