Estimating true digestibility of nonstructural carbohydrates in the small intestine of steers.

Four Angus steers (318 +/- 16 kg) fitted with ruminal, duodenal, and ileal cannulas were used in a 4 x 4 Latin square design to determine carbohydrate disappearance from the small intestine (SI). Steers were fed fescue hay at 1.8% of BW and abomasally infused with starch hydrolysate (SH) at 10, 20, or 40 g/h or glucose (G) at 30 g/h. Starch hydrolysate was raw cornstarch digested by a heat-stable alpha-amylase. Experimental periods were 10 d with 6 d of adaptation, 3 d of digesta and feces collection, and 1 d of rest. Glucose (% of infused) had greater (P < .001) apparent small intestinal and postruminal disappearance (% of infused) compared with 20 and 40 g/h SH. Starch hydrolysate infusion linearly increased (P < .001) apparent SI, large intestinal (LI), and total intestinal starch disappearance (g/d) and quadratically increased (P < .003) apparent SI and total intestinal starch disappearance (% of infused). Ileal starch flow from infusion increased quadratically (P < .03) as SH infusion increased. True SI and total intestinal starch disappearance increased linearly (P < .001; g/d) with SH infusion. However, SH infusion quadratically decreased (P < .02) efficiency of true SI starch disappearance (% of infused). True LI starch disappearance (g/d and % of infused) quadratically increased (P < .03) as SH infusion increased. These data demonstrate that, even in animals fed all-forage diets, there is a significant flow of alpha-glucosides, and these need to be considered when evaluating intestinal carbohydrate digestion.