Effect of glucoamylase and duration of silage storage on ruminal degradation and dry matter loss of corn and sorghum grain rehydrated and ensiled

Flint corn and sorghum grain are slow rumen degradable starch sources. Storing grain by rehydration and ensiling can improve ruminal degradability, by prolamin degradation in the silo. We evaluated the ruminal degradation and DM loss of rehydrated and ensiled grains of sorghum and flint corn (G) and the interaction of G with glucoamylase addition at ensiling (A) and duration of silage storage (D). Treatments were a 2 × 3 × 2 factorial combination of G (Sorghum, 129 µm geometrical mean particle size vs. Corn, 211 µm geometrical mean particle size), A (CTLvs. AMG vs. GAM), and D (30 d vs. 180 d). Dosage of glucoamylases AMG (AMG, Novozymes) and GAM (Sanferm Yield, Novozymes) was 0.35 mL/kg of grain. Mature grain was rehydrated to a targeted DM concentration of 65%. Approximately 4 kg of rehydrated grain was ensiled in 10 cm diameter × 60 cm length PVC silos with Bunsen valves (6 silos/ treatment combination). At opening, silages were frozen DM degradation in 0 (bag wash), 3, 6, 12, 18, and 48 h of incubation (3 rumen cannulated cows). Time 0 DM disappearance was the fast degrading Fraction A. The slowly degradable Fraction B was 100- Fraction A (a 2 pool model). The fractional rate of Fraction B degradation (kd) was calculated as the slope of the linear regression over time of the Ln of bag residue/incubated. Effective ruminal degradation (ERD6) was calculated as: A + B [kd/(kd + kp)], kp at 6%/h. Glucoamylases increased Fraction A, but had no effect on DM degradation at other incubation times and ERD6, and increased DM loss, especially in longer storage (P < 0.01 for the interaction of A and D). Corn had greater DM loss and kd than sorghum, but lower DM degradation up to 6 h of ruminal incubation and ERD6, the smaller particle size of ground sorghum may explain such response. Longer storage increased DM loss, kd, ruminal degradation at all incubation times, and ERD6. Glucoamylase increased the rapidly degradable grain fraction at the expense of increased DM loss. Longer storage increased ruminal degradation and DM loss. Rehydrated and ensiled sorghum was as degradable in the rumen as corn and had lower DM loss, but had lower starch concentration than corn.