PSVI-5 - Effects of exogenous glucoamylase enzymes or a combination with a neutral protease on total tract apparent digestibility and feces D-lactate in bulls fed a total mixed ration rich in rolled corn

The aim of this study was to evaluate the effect of 2 glucoamylases (GA) and the combination of one GA with a neutral protease on total tract apparent digestibility in bulls fed a total mixed ration (TMR) rich in rolled corn. Sixteen Angus beef bulls (266 ± 4.9 kg of initial BW, and 182 ± 1.7 d of age) were housed individually in pens and were distributed in 4 blocks of 4 animals balanced by BW. The experimental design was a 4 x 4 Latin square (4 blocks and 4 periods) with periods of 2 wks. Four treatments were tested; 1) control, a blank solution of 0.2% potassium sorbate and 0.6% sodium benzoate corresponding to the preservatives used in the enzyme preparation, 2) a GA preparation from Trichoderma reesei; 3) a GA preparation from Aspergillus fumigatus; 4) and a GA from Aspergillus fumigatus and a Bacillus amyloliquefaciens neutral protease preparation. These enzyme solutions were daily mixed was mixed in a dry TMR with 70% of rolled corn at a rate of 10 mL for 40 kg TMR. From day 8 to 14 chromium oxide (1 mg/kg) was mixed with the diet and from day 12 to 14 feces were collected to estimate total tract apparent digestibility and D-lactate concentration. Intake was recorded daily. Enzyme supplementation, regardless of enzyme type, increased (P < 0.05) DM (from 66.7% to 73.1% ± 2.01), OM (from 66.7% to 72.9% ± 2.03), and starch (from 74.7% to 81.8% ± 2.25) total tract apparent digestibility, and did not affect feces D-lactate concentration (1.26 vs 1.00 ± 0.200 mM for control and enzyme supplemented, respectively). So, any of the enzyme preparations tested (glucoamylases from Trichoderma reesei or Aspergillus fumigatus, or Aspergillus fumigatus glucoamylase n combination with the Bacillus amyloliquefaciens protease) increased by 9.5% starch digestibility.