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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 indicus) dairy cows under rotational grazing (Guinea Grass, Panicum maximum cv. Mombaca) 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 YDP0 (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.

We aimed to determine the effects of partially replacing conventional solvent-extracted soybean meal by amino resin-treated soybean meal in the concentrate supplement of lactating dairy cows grazing Guinea grass (Panicum maximum cv. Mombaca) on dry matter intake, milk production and composition, feed and nitrogen use efficiency, and nutrient digestibility. Eighteen Holstein x Gyr crossbred multiparous cows (79 ± 38 days in milk and 37.4 ± 4.69 kg/d of milk yield) were used in a replicated 3 × 3 Latin square design study with three experimental periods of 21 d The solvent extract soybean meal of the control diet (CON) was replaced by 1.0 (TSBM1.0) and 1.5 (TSBM1.5) kg as-fed basis of amino resin-treated soybean meal (29 and 43% as dry-matter basis, respectively) in the treatment diets. Dry matter intake, milk casein, protein, and fat contents, feed efficiency, nitrogen use efficiency, and nutrient digestibility did not differ among treatments (P > 0.05). The metabolizable protein was not increased by the treatments; however, cows fed with TSBM1.5 tended to produce 1.2 kg/d more milk (P = 0.09) and 64.3 g/d more lactose (P = 0.06) than CON cows. Although the supply of metabolizable protein was not affected by treatments, increasing rumen undegradable protein supply by 43% by replacing conventional solvent-extracted soybean meal with amino resin-treated soybean meal tended to increase milk production of high producing grazing cows.