PSXIV-5 Dietary replacement of soybean meal with heat-treated soybean meal to reduce dietary crude protein on milk production and rumen and blood parameters in lactating cows.

Abstract The objective of this study was to investigate the effect of dietary replacement of soybean meal (SBM) with heat-treated soybean meal (HTSBM) to reduce dietary crude protein (CP) on milk production and rumen and blood parameters in lactating cows. Holstein cows (n=22) were stratified by days in milk (112 ± 58 d), parity (2.5 ± 1.22), and milk yield (35.2 ± 1.76 kg/day), and randomly assigned to one of two dietary groups (SBM or HTSBM group] in a completely randomized design. All cows were fed the same total mixed ration (TMR) and the concentrate. During the TMR feeding, soybean meal (1,000 g) for the SBM group and both heat-treated soybean meal (500 g) and corn flake (400 g) for the HTSBM group were top-dressed twice daily at 0900 and 1500 h in equal portions over a 70-day period. The TMR consisted mainly of 34.5% TMR-mix, 14.3% oat hay, 12.3% alfalfa hay, 6.1% tall fescue, 10.4% timothy, 2.16% flaxseed, 4.14% cottonseed, 9.85% corn flake, and 0.87% protected fat. The SBM was replaced with fermented HTSBM to reduce CP level and increase rumen undegradable protein (RUP) level in the HTSBM group (CP: 16.2% of DM, RUP: 37.8% of CP) compared to the SBM group (CP: 16.9% of DM, RUP: 35.0% of CP). Data were analyzed using a mixed model with PROC MIXED in SAS version 9.4. There were no differences in dry matter intake, milk production (milk yield, fat-corrected milk, energy-corrected milk), and milk composition (fat, protein, lactose, somatic cell count, β-hydroxybutyrate, milk urea nitrogen). Ruminal ammonia concentrations were lower (p< 0.01) in the HTSBM group than in the SBM group. Ruminal total volatile fatty acid concentrations and acetate and propionate proportions and blood urea nitrogen concentrations were not different (p >0.05). In conclusion, replacing SBM with HTSBM did not affect milk production and compositions but reduced ruminal ammonia concentrations, indicating that reducing dietary CP by increasing RUP levels can be implemented in dairy production without negatively affecting cow performance.