341 Influence of dry-rolled corn processing and distillers grain inclusion rate on ruminal digestive enzyme activity.

Ruminal enzymes play a critical role in the breakdown and metabolism of nutrients. To determine the effect of degree of dry-rolled corn processing on ruminal α-amylase, trypsin and maltase activity, 8 ruminally and duodenally cannulated Holstein steers (526 ± 3.6 kg) were used. Treatments were assigned in a 2 × 2 factorial arrangement consisting of 1) 65% coarse-rolled corn (2.5 mm) with 20% dried distillers grains with solubles (DDGS), 2) 45% coarse-rolled corn with 40% DDGS, 3) 65% fine-rolled corn (1.7 mm) with 20% DDGS and 4) 45% fine-rolled corn with 40% DDGS. Diets were formulated with 10% forage and calculated to meet or exceed NRC recommendations and were offered for ad libitum intake. The experiment was designed as a 4 × 4 Latin square with 7 d of diet adaptation and 7 d of sample collection. To determine enzyme activity, approximately 200 mL of ruminal fluid were sampled from d 3 to 5 in a manner representing every other hour in a 24-h cycle. Data were analyzed using the Mixed procedure of SAS (SAS Inst. Inc., Cary, NC). Activity of α-amylase (U/L of ruminal fluid, α-amylase/kg starch disappearance) was greater (P ≤ 0.001) in diets containing 20% DDGS compared with 40% DDGS. Diets containing fine-rolled corn and 40% DDGS had greater (interaction: P = 0.01) trypsin activity (U/kg CP disappearance). Maltase activity (U/L of ruminal fluid) also demonstrated an interaction (P = 0.004) with diets containing coarse-rolled corn and 40% DDGS having the least activity. In conclusion, α-amylase activity was greater in diets containing 20% DDGS, likely because of additional starch provided in rations containing more corn. Trypsin activity was greater in diets with 40% DDGS compared with the 20% DDGS diet which likely was caused by increased protein intake. Digestive enzyme activity of ruminal microbes responded to changes in nutrient composition resulting from variation in DDGS inclusion more so than variation in particle size of dry-rolled corn.