The influence of intake level and corn processing on digestibility and ruminal metabolism in steers fed all-concentrate diets.

The effects of intake (ad libitum and 70% of ad libitum) and corn processing (whole or rolled) on digestion, ruminal metabolism, and blood metabolites were determined in a 2 x 2 factorial experiment using eight ruminally fistulated steers. All-concentrate diets were fed with adjustments to dietary concentrations of N, vitamins, and minerals to ensure equal daily intake of these nutrients. Digestion of DM, OM, and starch were affected by an intake x processing interaction (P < .03). Starch digestion for the low-intake, whole-corn diet was much lower than that for the other three diets. This decrease in starch digestion was the major reason for the interaction. Nitrogen digestion was improved (P < .03) with limited intake but was not affected by processing. Ruminal volume and ruminal turnover (percentage/hour) were both reduced (P < .03) on the low-intake diet. Molar proportion of acetate was reduced and propionate was increased (P < .01) for steers receiving high intake of rolled corn compared with the other three diets. Butyrate concentrations were increased (P < .01) when corn was rolled before feeding. Ruminal pH was higher immediately before feeding for steers receiving whole corn than for those receiving rolled corn. Decreases in pH were observed for rolled corn 2 to 9 h after feeding, suggesting a faster rate of fermentation of rolled corn than of whole corn. Concentrations of blood glucose and insulin were not affected by intake or processing. It was concluded that processing corn can improve DM and OM digestibility if intake is restricted and that N digestion is improved with restricted feeding.(ABSTRACT TRUNCATED AT 250 WORDS)