Dose-response of amylolytic enzyme on nitrogen utilization and live weight of dairy cows

The aim of the current study was to determine the effects of increasing dietary levels of amylolytic enzyme on nitrogen utilization and live weight of lactating dairy cows. Twenty-four Holstein cows [162 ? 107.9 days in milk, 31.6 ? 6.5 kg/d of milk yield and 636.3 ? 62.35 kg of live weight (LW) at the start of experiment, mean ? SD] were used in a 4 x 4 Latin square design experiment with 21-d periods (the last 7 d for sampling). Cows received four treatments: Control (CON); or CON containing 150, 300 and 450 FAU/kg DM. One FAU (fungal ?-amylase unit) is the amount of enzyme which breaks down 1 g starch in 1 h at pH 4.7 and 30?C. The enzyme comes from an Aspergillus oryzae extract, enriched with ?-amylase activity (Amaize, Alltech Inc., Nicholasville, KY, USA), and was supplied as a dry powder mixed with the concentrate. Diet was composed of 50% of corn silage and 50% of grain mixture. The feed offered and refusals were weighed daily, and samples of feed ingredients and orts were collected during the sampling period to determine N and indigestible acid detergent fiber (iADF) content and intake using micro-Kjeldahl and in situ incubation methods, respectively. Feces were collected every 9 h from d 16 until d 18 of each period to form a composite sample which were also analyzed for N and iADF to determine the total excretion of nitrogen in feces. Cows were milked twice daily, and samples were collected on d 15, 16 and 17 of each experimental period. Milk samples were analyzed for N and corrected to protein content (N x 6.38). Urine samples were collected at the same time of feces and daily urinary volume was determined based on creatinine concentration measured using colorimetric method, and N content of urine was determined. Cows were weighed after the first milking on d 14 and 21 of each period. Data were submitted to simple polynomial regression using the PROC MIXED of SAS 9.4. Treatments did not alter N intake and N excretion in urine, but tended to linearly decrease (P = 0.061) fecal N, and decreased (P = 0.023) N in milk. Enzyme linearly increased (P = 0.039) the LW of animals. Amylolytic enzyme altered nitrogen utilization and increased the live weight of dairy cows.