LAUSR

Abstract This study was designed to evaluate increasing dietary doses of an Aspergillus oryzae extract with alpha-amylase activity on nutrient intake and total tract digestion, sorting index, ruminal fermentation, milk yield and composition, blood metabolites and nitrogen utilization of mid- to late lactating dairy cows. Twenty-four multiparous Holstein cows (162.3 ± 107.9 days in milk, 636 ± 62 kg of live weight, and 31.6 ± 6.5 kg/d of milk yield) were used in a replicated 4 × 4 Latin square design experiment. Eight cows used in the experiment had rumen cannulas to assess ruminal fermentation variables. Periods had 21 days, in which 14 days were allowed for treatment adaptation and 7 days for sampling. Cows were randomly assigned to the following treatments: control (A0), and Aspergillus oryzae extract to supply 150,300 or 450 FAU/kg DM. One FAU (fungal amylase unit) is the amount of enzyme which will dextrinize soluble starch at the rate of 1-mg per minute at 30 °C and pH 4.8. Treatments did not affect DM and nutrient intake, as well as the sorting index of cows. Alpha-amylase supplementation linearly increased ( P  = 0.031) crude protein digestibility and tended to linearly increase ( P  = 0.060) DM digestibility. Treatments did not affect ruminal pH, acetate, butyrate, propionate and total branched-chain fatty acids. Alpha-amylase linearly increased ( P  = 0.023) isovalerate production and tended to quadratically affect ( P  = 0.065) ammonia nitrogen concentration in rumen. Milk yield and composition, and efficiency of milk production were not affected ( P  ≥ 0.275) by alpha-amylase supplementation. Treatments tended to linearly decrease ( P  = 0.061) N excreted in feces. Treatments linearly increased ( P  ≤ 0.039) live weight and body condition score of cows. Finally, alpha-amylase supplementation did not affect ( P  ≥ 0.234) serum glucose, urea, and hepatic enzymes concentration. Increasing doses of an Aspergillus oryzae extract up to 450 FAU/kg DM did not alter starch digestibility, ruminal propionate production, microbial protein synthesis, and milk yield and composition of mid-lactating cows.