Effect of exogenous glucoamylase on ruminal in situ and in vitro dry matter and starch degradability of cereal grains in beef cattle.

Objective: To evaluate the effects of glucoamylase on ruminal in situ and in vitro dry matter degradability (DMD), in vitro starch degradability (IVSD), volatile fatty acids (VFA), gas production and methane production using cereal grains as substrates in beef cattle.

Methods: Six substrates (4 mm; 0.70 g per F57 bag) including sorghum (micronized and whole), barley (whole and steam-flaked), and corn (dry-rolled and steam-flaked); were incubated with exogenous glucoamylase (from Trichoderma reesei; 0.25 mg/g substrate DM) and buffered rumen fluid in six replicates per run in 3 independent runs. In vitro dry matter degradability (IVDMD), In vitro starch degradability (IVSD), In situ DMD (ISDMD), VFA, and methane production was measured after 7, and 12 h of incubation. In situ ruminal DMD (ISDMD) was measured after 0, 1, 3, 7, and 12 h of ruminal incubation in beef cattle fed high grain diets.

Results: Exogenous glucoamylase increased IVDMD and gas production for all substrates except whole sorghum and barley while ISDMD was increased for all substrates except whole barley. Glucoamylase increased IVSD for steam flaked barley and corn. Glucoamylase supplementation increased molar proportion of propionate and decreased acetate-to-propionate ratio, regardless of substrates used. Similarly, glucoamylase supplementation increased methane production with steam-flaked corn.

Conclusion: Glucoamylase supplementation can potentially improve DM and starch degradability in cereal grains commonly used as ingredients in beef cattle diets.