Partial substitution of soybean meal with a yeast-derived protein in the diet of dairy cows under a rotational grazing system

This study's aim is to evaluate the substitution of soybean meal with a yeast-derived protein (YDP) in the diet of F1 Holstein (Bos Taurus) x Gyr (Bos indices) dairy cows under rotational grazing (Guinea Grass, Panicum maximum cv. Mombasa) and to analyze the effects on milk yield, milk solids percentage, blood parameters, and feed efficiency (FE). Sixteen Holstein X Gyr (F1) multiparous cows with an average of 30 +/- 1.8 kg/d (Mean +/- SD) of milk, 489 +/- 22 kg of body weight, and 62 +/- 26 days in milk (DIM), at the beginning of the study, were assigned to four squares based on their DIM, milk yield, and parity. The experimental diets were based on the substitution of soybean meal with a YDP in equal proportions: treatment YDPO (without a YDP), treatment YDP150 (substitution of 150 g of soybean meal with a YDP), treatment YDP300 (substitution of 300 g of soybean meal with a YDP), and treatment YDP450 (substitution of 450 g of soybean meal with a YDP). The substitution of soybean meal with a YDP in the diets of dairy cows under rotational grazing linearly decreased milk and solids production and affected the neutral detergent fiber (NDF) intake, without affecting the total feed intake. No difference was found in the microbial protein synthesis between treatments. FE tended to be lower at high inclusions of the YDP.