The relations between the apparent digestibility of roughages in the rumen and lower gut of sheep, the volume of fluid in the rumen and voluntary feed intake

Three sheep with permanent fistulas of the rumen were each given dried grass and two hays, each in three different amounts, and the apparent digesti-bility of the roughages in the rumen and distal to the rumen was determined. A lignin ratio method was used to measure digestibility. With increase in the amount of the poorest hay given, the proportion digested in the rumen fell and that distal to the rumen increased. With the second hay this effect was also noted but was not statistically significant. The voluntary intakes ofdry matter varied from 1·94 kg/day for the dried grass to 1·28 for the poorest hay. The volumes of distribution of polyethylene glycol in the rumen when feed was offered ad libitum, however, were the same, irrespective of the type of feed, at between 14·1 and 15·2 litres. These observations were confirmed at slaughter. The results support the hypothesis that sheep voluntarily consume roughages of different qualities to achieve constant fill of their rumens, and that little regulation of voluntary intake can be attributed to distension of the hind gut.