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.

Carbohydrate digestion and glucose supply in the gut of the ruminant

“…Theoretical yields of VFA consisting, on a molar basis, of 65% acetic acid, 25% propionic acid and 10% n-butyric acid (65:25:10) are about 1.2 mol/Ioo g polysaccharide fermented when calculated according to stoichiometric principles (Walker & Nader, 1970) and about 1-3 mol/Ioo g OM fermented when based on the measurement of apparent energy digestion in the rumen (Nicholson & Sutton, 1969). In vivo measurements by isotope dilution procedures suggest that production is about 1.5 mol/Ioo g OM fermented (Hogan, Weston & Lindsay, 1969); in vitro techniques yield values about 35% lower than this and are almost certainly in error (Whitelaw, Hyldgaard-Jensen, Reid & Kay, 1970).…”

“…When roughages are given alone and in the chopped or long form, about 5 5 7 0 % of the digestible OM is fermented in the rumen (Weston & Hogan, 1968 When mixed rations of hay and concentrates are given, the proportion of digestible OM fermented in the rumen averages about 65-75% (Hogan & Weston, 1967b;Nicholson & Sutton, 1969;Sutton, Smith & Corse, 1970) and probably results in the production of about 0.8-0.9 mol VFA for every IOO g OM digested throughout the tract. For high-concentrate rations, the amounts of glucogenic VFA produced would vary widely according to whether high-propionate or high-butyrate fermentations developed.…”

Feed evaluation by measurement of sites of digestion in cannulated ruminants

“…Increases in level of intake reduce methane losses, alter volatile fatty acid proportions in the rumen and decrease ADOM. It is not known to what extent factors required by the proposed scheme are affected, but a reduction in ADOM," has been reported at higher levels of intake in sheep (Nicholson & Sutton, 1969). Clearly there is an urgent need to determine values for the required factors in milking cows receiving production rations or to establish whether sheep fed near to maintenance provide an adequate model for growing and lactating cattle.…”

Quantitative microbial protein synthesis in the bovine rumen

“…If one assumes that the diet fed was approxi mately 90% dry matter, 9.8 and 10.4 g microbial protein was synthesized per 100 g of dry matter intake of the semipurified diets without and with DES, respectively. The amount of dry matter that left the rumen was not estimated; however if 607» of the dry matter was assumed digested in the rumen (Nicholson and Sutton, 1969) One effect of dilution rates has been shown by studies in which the amount of dry cells synthesized increased from 10 to 20 grams as dilution rate increased (Hobson, 1965;Hobson and Summers, 1967). These in vitro ex periments indicate that bacterial protein yields from fermentation vary with species of microorganisms present, substrate concentration, type of culturing system used, and dilution rates.…”

“…^Purchased from the Rowett Research Institute, into the rumen through the fistulas every 12 hours for 7 days prior to and throughout each collection period as described by Nicholson and Sutton (1969).…”