The effect of diet composition and level of feeding on digestion in the stomach and intestines of sheep

Abstract

1. Four wether sheep, each fitted with re-entrant duodenal cannulas and a rumen cannula, were used to determine the relative quantitative importance of digestion in the stomach compared with that in the intestines when diets of low (HM1) and high starch (CM1) content were fed at 0.9 times maintenance and when the high-starch diet was fed at 1.7 (CM2) and 2.3 (CM3) times maintenance. Paper, impregnated with chromic oxide, and polyethylene glycol (PEG) were administered.2. An apparatus is described which allowed one operator to collect, record, sample and return the duodenal digesta from two sheep simultaneously.3. Total digestion was determined by faeces collections over 7–10 day periods, and digestion in the stomach by measuring the total flow of digesta from the abomasum to the duodenum over two 24 h periods with two or three sheep on each ration. Flow values were adjusted to give 100% recovery of chromic oxide.4. The recoveries of chromic oxide and PEG were similar and it was concluded that either marker was satisfactory for adjusting 24 h flow values. Disadvantages of using PEG are discussed.5. There was relatively little difference between rations HM1 and CM1 in the proportion of digestible organic matter and energy digested in the stomach. Only 57.1% of the total dry-matter digestion occurred in the stomach for ration HM1 compared with 65.0% for ration CM1 reflecting a smaller net gain in ash for ration CM1. Doubling the level of intake (ration CM2) resulted in a decrease in the proportion of digestible dry matter, organic matter and energy digested in the stomach. When the level was increased still further with ration CM3, the proportion continued to decrease with one sheep but increased with the other.6. All but 5–11% of the digestible starch (measured as α-linked glucose polymer) was fermented in the stomach, the lowest proportion being with ration HM1.7. The amount of nitrogen reaching the duodenum was approximately equal to the amount ingested with rations HM1 and CM1 but considerably greater with the other two rations. All rations contained approximately 2% nitrogen.8. Calculation of the estimated loss of energy as methane and heat of fermentation suggested that 50–54% of the digestible energy was absorbed as volatile fatty acids.