In vitro gas production kinetics are influenced by grain processing, flake density, starch retrogradation, and Aspergillus oryzae fermentation extract containing α-amylase activity.

Grain processing such as particle size, flake density, or starch retrogradation can influence ruminal degradability characteristics; however, it is unclear how exogenous α-amylase supplementation interacts with different processed grains. Four experiments were conducted to compare the effects of Aspergillus oryzae fermentation extract (Amaize®; Alltech Biotechnology Inc., Nicholasville, KY) supplementation on in vitro gas production kinetics of grain substrates with different processing methods that are common in the feedlot industry. In Exp. 1, corn processing (dry-rolled, high-moisture, steam-flaked) and Amaize supplementation (0 or 15 U α-amylase activity/100 mL) were evaluated in a 3 × 2 factorial arrangement of treatments. The rate of gas production for dry-rolled corn was higher (P < 0.001) with Amaize supplementation. In Exp. 2, flake density (296, 322, 348, 373, and 399 g/L) and starch retrogradation (storage in heat-sealed foil bags for 3-d at 23ºC or 55ºC) were evaluated in a 5 × 2 factorial arrangement of treatments. There was a flake density × starch retrogradation interaction (P < 0.01) for the rate of gas production because the decrease in the rate of gas production with starch retrogradation was greater at lighter flake densities compared with heavier flake densities. In Exp. 3, Amaize supplementation was evaluated across flake densities of non-retrograded steam-flaked corn (stored at 23ºC) used in Exp. 2. There was a flake density × Amaize interaction (P < 0.01) for the rate of gas production where Amaize supplementation resulted in a lower rate of gas production at lighter flake densities (296, 322, and 348 g/L) but a higher rate of gas production at heavier flake densities (373 and 399 g/L). In Exp. 4, Amaize supplementation was evaluated across flake densities of retrograded steam-flaked corn (stored at 55ºC) used in Exp. 2. Gas production was lower after 24-h with Amaize supplementation for retrograded flakes produced to a density of 322 g/L and 399 g/L while Amaize supplementation did not influence gas production at 24-h at other flake densities. There was a flake density × Amaize interaction for the rate of gas production because Amaize supplementation resulted in a faster (P < 0.01) rate of gas production for all flake densities except retrograded flakes produced to a density of 296 g/L. Enzymatic starch availability was positively correlated with the rate of gas production. These data demonstrate that supplementation of 15 U/100 mL of Amaize resulted in greater rates of gas production for dry-rolled corn, corn steam-flaked to heavier densities, and retrograded steam-flaked corn.