Effect of protein source and soluble carbohydrate addition on rumen fermentation and lactation performance of Holstein cows

Rumen in vitro and in vivo experiments were conducted to evaluate the effec t of rumen undegradable protein and soluble carbohydrates on rumen ammonia N release and lactation performance of Holstein cows. In the in vitro exper iment, freeze-dried annual ryegrass (Lolium multiflorum, LAM) pasture was s upplemented 1:1 with ground corn-based grain supplements containing expelle r or solvent soybean meal with sucrose or lactose supplements at 0, 2.5, or 5% of dry matter (DM). The ammonia release rate was slower with expeller c ompared with solvent soybean meal-supplemented diets. Sucrose supplementati on at the 5% level lowered rumen ammonia concentrations, but lactose-fortif ication of grain supplements was without effect. In the in vivo study, 32 m ultiparous Holstein cows were blocked according to milk yield and randomly assigned to corn-based grain supplements containing 1) solvent soybean meal , 2)solvent soybean meal + 5% sucrose supplement, 3) expeller soybean meal, or 4) expeller soybean meal + 5% sucrose supplement. Grain supplements and fresh annual ryegrass were component fed at approximately a 1:1 grain to f orage ratio (DM basis). Forage DM intake was higher for cows receiving solv ent soybean meal supplemented grain supplements than those receiving expell er soybean meal (12.2 +/- 2.1 vs. 11.4 +/- 2.2 kg/d), but total DM intake w as similar for all diets (22.8 +/- 2.9 kg/d). Fat-corrected milk yield was similar for all diets averaging 37.5, 38.2, 39.1, and 37.6 kg/d for diets 1 to 4, respectively. Rumen fermentation, milk urea nitrogen, and body condi tion were unaffected by supplements; however, cows fed grain supplement 1 u tilized dietary energy more efficiently than cows offered the other dietary treatments. High dietary crude protein concentrations may have limited lac tation response to rumen undegradable protein and sugar.