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Influence of substrates on efficacy of exogenous glucoamylase on in vitro dry matter digestibility, pH, and gas production.

D. Vyas



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Influence of substrates on efficacy of exogenous glucoamylase on in vitro dry matter digestibility, pH, and gas production.
L. Mu1, K. G. Arriola1, G. Hao1, H. Sultana1, A. Oyebade1, F. X. Amaro1, K. Almeida1, C. Heinzen1, J. O. Gusmao1, C. A. Nino de Guzman1, I. Fernandez1, W. Li2, S. Yu3, D. Vyas*1. 1University of Florida Gainesville, FL, 2DuPont Nutrition & Biosciences Wilmington, DE, 3DuPont Nutrition & Biosciences Aarhus, Denmark.

The objective was to evaluate the effect of exogenous glucoamylase supplementation on ruminal in vitro dry matter (IVDMD), pH, and gas production of different cereal grains used for livestock production. Five substrates (4 mm; 0.5 g per F57 bag) including sorghum (micronized and whole), barley (whole and steam-flaked), and corn (steam-flaked); were incubated with exogenous glucoamylase (from Trichoderma reesei; 0.25 mg/g substrate DM) and buffered rumen fluid for 7 h in 6 replicates per run in 3 independent runs per experiment. Gas production was measured at 0, 2, 4, and 7 h while DMD, and pH was measured after 7 h of incubation. Rumen fluid was collected from 3 rumen-cannulated lactating dairy cows fed corn silage-based diet formulated based on NRC (2001) guidelines. Data were analyzed using the GLIMMIX procedure of SAS. Treatments and sampling time (for gas production) were used as fixed effects while run was considered random factor. Exogenous glucoamylase had no effect on DMD of micronized sorghum (P = 0.21); however, DMD was increased by 10, 32, 19, and 59% with whole sorghum (P = 0.03), whole barley (P = 0.04), steam-flaked barley (P = 0.05), and steam-flaked corn (P = 0.04). Cumulative gas production was increased with glucoamylase when whole (P < 0.01) and steam-flaked barely (P = 0.03) while tendency was observed with steam-flaked corn (P = 0.07). No treatment effects were observed on pH values except with steam-flaked corn where pH was reduced with glucoamylase supplementation (6.65 vs 6.81; P = 0.03). The interaction between glucoamylase and sampling time resulted in greater gas production with amylase treated whole and steam-flaked barley after 4 and 7 h of incubation (P = 0.03). Similarly, the interaction effect tended to increase gas production for amylase treated steam-flaked corn after 4 and 7 h of incubation. In conclusion, IVDMD was increased with exogenous glucoamylase supplementation when whole sorghum, whole and steam-flaked barley, and steam-flaked corn was used as substrate.

Keywords: amylase, in vitro dry matter digestibility (IVDMD), gas production.