Effect of roll clearance of mechanical processing of corn silage harvested at the black-line stage of maturity on carbohydrate and protein utilization in dairy cows.

The experiment was conducted to evaluate the effect of roll clearance of mechanical processing of whole plant corn silage (CS) on carbohydrate and protein utilization in dairy cows. Treated CS was harvested at the black-line stage of maturity and chopped at a theoretical length of cut (TLC) of 9.5 mm without processing or at a TLC of 19 mm with processing at a roll clearance of 1, 3 and 5 mm. Four ruminally and duodenally cannulated dry cows were assigned to a 4 × 4 Latin square design for 14-day periods. Cows were fed diets containing 77% CS and 23% soybean meal (dry matter basis) to equalize the crude protein supply. Mechanical processing had no significant effect on dry matter intake and neutral detergent fiber digestibility. Ruminal and total tract starch digestibility and total digestible nutrients tended to be higher with processing at a roll clearance of 1 or 3 mm than at 5 mm. Microbial nitrogen efficiency in cows did not differ among all treatment groups. These results suggest that when CS is harvested at the black-line stage of maturity, roll clearance should be 3 mm or less with a TLC of 19 mm.