Replacing soybean meal with okara meal: Effects on production, milk fatty acid and plasma amino acid profile, and nutrient utilization in dairy cows

Okara meal is a byproduct from the production of soymilk and tofu and can potentially replace soybean meal (SBM) in dairy diets due to its high crude protein (CP) concentration and residual fat. The objective of this study was to investigate the effects of replacing SBM with okara meal on feed intake, yields of milk and milk components, milk fatty acid (FA) profile, nutrient utilization, and plasma AA concentration in lactating dairy cows. Twelve multiparous (65 ± 33 d in milk) and 8 primiparous (100 ± 35 d in milk) organically certified Jersey cows were paired by parity or days in milk, and within pair, randomly assigned to treatments in a crossover design with 21-d periods (14 d for diet adaptation and 7 d for data and sample collection). Diets were fed as total mixed ration formulated to be isonitrogenous and isofibrous and contained (dry matter basis) 50% mixed, mostly grass baleage, 2% sugarcane liquid molasses, 2% minerals-vitamins premix, and either (1) 8.1% SBM, 10% soyhulls, and 27.9% ground corn (CTRL); or (2) 15% okara meal, 8% soyhulls, and 23% ground corn (OKR). Dietary CP, ash-free neutral detergent fiber, and total FA averaged 15.4, 35.3, and 3.08% for CTRL and 15.9%, 36.3%, and 3.74% for OKR, respectively. Substitution of SBM with okara meal did not alter dry matter intake but increased intakes of CP and ash-free neutral detergent fiber. Additionally, no significant differences between treatments were observed for yields of milk and milk components, and concentrations of milk fat, lactose, and total solids. However, milk true protein concentration was lower in cows fed OKR (3.76%) versus CTRL (3.81%). Both milk urea N (8.51 vs. 9.47 mg/dL) and plasma urea N (16.9 vs. 17.8 mg/dL) concentrations decreased with OKR relative to the CTRL diet, respectively. Compared with CTRL, feeding OKR lowered the milk proportions of total odd-chain FA, de novo FA, and mixed FA and increased those of preformed FA, total n-6 FA, and total n-3 FA. The milk proportions of trans-10 18:1, trans-11 18:1, and cis-9,trans-11 18:2 were greater with feeding OKR versus the CTRL diet. The apparent total-tract digestibility of nutrients, urinary excretion of total purine derivatives (uric acid plus allantoin), and total N were not affected by treatments. Except for plasma Leu, which was lower in OKR compared with the CTRL diet, no other significant changes in the plasma concentrations of AA were observed. The plasma concentration of carnosine was lowest in cows receiving the OKR diet. Overall, our results revealed that okara meal can completely replace SBM without negatively affecting production and nutrient digestibility in early- to mid-lactation Jersey cows. Further research is needed to assess the economic feasibility of including okara meal in dairy diets, as well as the amount of okara meal that maximizes yields of milk and milk components in dairy cows in different stages of lactation.