Dietary replacement of soybean meal with heat-treated fermented soybean meal affects milk production and nitrogen efficiency in lactating dairy cows

Objective The purpose of this study was to see how reducing dietary crude protein (CP) and rumen degradable protein while increasing rumen undegradable protein (RUP) afffected milk yield and composition, nitrogen (N) metabolism, and rumen and blood parameters in Holstein lactating cows. Methods Holstein cows (n = 13) were stratified by days in milk (91.75±32.39), parity (2.58±1.44), and milk yield (42.86 kg±6.6), and randomly assigned to one of two dietary groups (soybean meal [SBM] or heat-treated fermented soybean meal [HFSBM] group) in a completely randomized design. Results There were no differences in dry matter intake, milk production, or milk composition (fat, protein, lactose, somatic cell count, β-hydroxybutyrate, and milk urea N). Ruminal ammonia concentrations were lower in the HFSBM group than in the SBM group. Ruminal total volatile fatty acid concentrations, acetate and propionate proportions, and blood urea N concentrations did not differ. Calcium levels in the blood were lower both before feeding (0 h) and 3 h post-feeding in the HFSBM group compared to the SBM group. Total protein levels in blood were higher in the HFSBM group. There were no differences in digestibility of dry matter or CP. The neutral detergent fiber and N outputs from feces and urine did not differ. N efficiency tended to be higher in the HFSBM group. Conclusion Replacing SBM with HFSBM did not affect milk production but reduced ruminal ammonia concentrations, indicating that reducing dietary CP by increasing RUP levels can be implemented in dairy production without negatively impacting cow performance.