The digestion of chopped and ground roughages by sheep. II. Digestion of nitrogen and some carbohydrate fractions in the stomach and intestines

Abstract

A study of the intake and digestion of lucerne and wheaten hays was made with Merino wethers offered chopped hay near ad libitum, ground hay at the same level as the chopped hay, and ground hay near ad libitum. These treatments were imposed to separate the effects of grinding per se from those associated with the increased intakes of roughages permitted by grinding. The following conclusions were reached:

(1) Grinding permitted a substantial increase in food consumption on both diets.

(2) Grinding per se of both hays produced little change in the relative importance of stomach and intestines as sites of digestion of any of the feed components studied. Grinding had no effect on the digestibility of lucerne hay but reduced that of wheaten hay, mainly by reducing the digestion of the cell wall constituents.

(3) When both ground hays were offered near ad libitum, digestibility was reduced, mainly because of a fall in digestibility of the cell wall constituents. With lucerne hay, grinding increased the organic matter intake by 37% above chopped hay but the organic matter digested was increased by only 27%. By contrast, on wheaten hay an increase of 42% in organic matter intake on ground hay resulted in the digestion of only 18% more organic matter than on chopped hay. On both diets the relative extent of digestion occurring in stomach and intestines was similar to that observed with chopped hay.

(4) On all three lucerne diets there was a net loss of 22–25% of dietary nitrogen from the stomach. By contrast, on the wheaten hay diets a substantial gain of nitrogen occurred during the passage of digesta through the stomach; the amount of nitrogen gained was independent of feed processing and feed intake. The crude protein apparently digested in the intestines was approximately 17% of the total organic matter digested on the lucerne diets and 10–12% of that digested on the wheaten hay diets.

(5) Within diets the relative proportions of individual rumen VFA were the same on chopped and ground hay offered near ad libitum.

(6) Grinding probably did not cause any change in the composition of the end products of digestion.

(7) On the lucerne hay diets, 16–20% of the organic matter digested in the rumen was soluble carbohydrate, on wheaten hay approximately 40–50%.