Intestinal Starch Digestion in Sheep Fed Different Rations with Abomasal Starch Infusion

Abstract

Four sheep were each fitted with an abomasal simple cannula and an ileal re-entrant cannula, and fed four rations at the maintenance energy level. The rations consisted of 30% concentrate and 70% chopped hay or 70% alfalfa meal pellets, and 70% concentrate and 30% chopped hay or 30% alfalfa meal pellets on a digestible energy basis. The concentrate contained mainly ground corn and soybean meal. Two digestion trials for each ration were conducted; in the first trial, animals were fed ration alone, and then in the second were fed the same ration with continuous infusion of purified corn starch into the abomasum, averaging 113g per day, equivalent to 0.2 times maintenance energy. The ingested starch digestibilities for the high-roughage rations were lower than those for the high concentrate rations in the rumen and small intestine, when expressed as percentages of the entered amount. Conversely, the large-intestinal digestibilities for the high-roughage rations became higher, but the total digestibilities tended to be lower in comparison with the high-concentrate rations. The treatment means of the small-intestinal digestibility of infused starch decreased from 86.0% with 30% chopped hay to 75.1% with 70% chopped hay as the amount of neutral detergent fiber entering intestine increased. However, the ration containing a high level of concentrate and a low amount of alfalfa meal pellets showed a considerably low digestibility of 45%, despite having the lowest amount of intestinal fiber. In such a ration, a higher content of long-chain polymers in α-glucoside fractions of ileal digesta suggested a lower action of α-amylase in the small intestine. As the greater digestibility of infused starch in the large intestine compensated for the lower digestibility in the small intestine, the total intestinal digestibility for each treatment was over 93%, and not different. It is thus considered that starch digestion is not affected by other ingested components throughout the whole intestine, but is variable in the small intestine.