I. The interaction between nitrogen and water intake was studied in two ewes and two red deer hinds. They were given pelleted diets, at maintenance level, containing equal amounts of roughage but either rich or poor in nitrogen. The deer received 5 0 yo more food than the sheep.Water was given either in large amounts (sheep 5.0 1, deer 7.0 1 daily) or in small amounts (sheep 1 . 1 1, deer 2.4 1 daily). 2.Nearly three-quarters of the nitrogen of the high-nitrogen rations but less than half of that of the low-nitrogen rations was excreted in the urine. Restriction of water intake reduced urinary nitrogen excretion by only about I g daily, mainly as a result of decreases in the excretion of urea and ammonia, but did not affect the excretion of nitrogen in the faeces.3. The urinary excretions of creatinine, creatine, hippuric acid, uric acid and allantoin were also examined. The excretion of creatinine was not related to either nitrogen or water intake. The excretion of uric acid and of allantoin was greater in the sheep than in the deer.4. The concentrations of urea in the plasma and of ammonia in the rumen fluid were measured before and after feeding. The plasma urea value was related to dietary nitrogen intake and was higher on the low-than on the high-water regime. The rumen ammonia value also was related to the nitrogen intake but, while it generally increased after feeding when the high-nitrogen diet was given, it fell almost to zero z h after feeding when the low-nitrogen diet was given.5 . The sheep digested dry matter, cellulose and nitrogen a little more fully than the deer. The high-water regime slightly increased the digestibility of dry matter and cellulose but did not affect the digestibility of nitrogen.

I. The flow of digesta to the abomasum and through the duodenum and terminal ileum was measured over 24 h periods in sheep. Pelleted diets of concentrates, principally composed of barley, and of poor-quality hay were given. The seven Scottish Blackface ewes studied were all fitted with rumen cannulas, and in addition two had simple abomasal cannulas, one a re-entrant abomasal cannula, two re-entrant duodenal cannulas, and two re-entrant ileal cannulas.2. Paper impregnated with chromium sesquioxide was given twice daily by rumen fistula. The amounts of dry matter, starch, cellulose, total nitrogen and energy passing through the abomasum, duodenum and ileum and the amounts excreted in the faeces were measured.Thc flows of digesta were adjusted to give 100 % recovery of chromium sesquioxide and the extent of digestion in various parts of the alimentary tract was calculated using these adjusted values. Concentrations of glucose in the blood and of volatile fatty acids (VFA) in the rumen were also measured.3. For the concentrate diet, 69 yo of the digestible dry matter disappeared in the stomach (reticulo-rumen, omasum and abomasum), 17 % in the small intestine and 14 % in the large intestine. Values for disappearance of digestible energy were 7 2 % in the stomach, 23 Yo in the small intestine and 5 % in the large intestine. Of the 298 g starch fed daily only 6-35 g passed through the abomasum or duodenum and only 1-4 g reached the terminal ileum. The cellulose in the diet was poorly digested. 4.For the hay diet, 67 % of the digestible dry matter disappeared in the stomach, 7.2 % in the small intestine and I I yo in the large intestine. Values for disappearance of digestible energy were 81 yo in the stomach, 7 yo in the small intestine and 12 yo in the large intestine.Of the 33 g of starch consumed daily, from 5 to 13 g passed through the abomasum or duodenum. The cellulose in the hay was 59 % digestible and virtually all this digestion took place in the stomach.5. The concentration of VFA and the proportion of propionate in the rumen fluid, 2.5 h after feeding, were considerably greater on the concentrate diet than on the hay diet, but diet had little influence on the concentration of blood glucose.6 . The importance of the small amount of starch passing to the sheep's small intestine is discussed.The volume and composition of the digesta passing through various sections of the digestive tract of sheep can be measured directly by causing the digesta to flow through re-entrant cannulas inserted into either the duodenum or terminal ileum (

The food eaten by sheep is digested in three stages. It is first fermented by micro-organisms in the reticulo-rumen where about two-thirds of the organic matter is degraded and absorbed. Food residues, saliva and the micro-organisms themselves then pass on to the abomasum and small intestine where they are exposed to acid and enzymes secreted by the sheep. What remains finally flows into the large intestine where it is subjected to microbial attack a second time and where water and salts are absorbed. A considerable amount is known about ruminal digestion but much less about the changes that occur in the small and large intestines, and the experiments described in this paper were undertaken to measure the digestion of cellulose and nitrogenous substances and the absorption of water and electrolytes by the large intestine. A brief summary of the results has been published (Goodall & Kay, 1962).Conscious sheep were used fitted with re-entrant cannulae in the terminal ileum. These diverted the flow of digesta to the large intestine through an external loop and by comparing the intake of food, the flow through the loop and the output of faeces over 24 hr periods, the extent of digestion and absorption of various components of the diet occurring before and after the point of cannulation were measured. This technique has previously been used by Hogan & Phillipson (1960) in sheep, by Smith (1962 in calves and by Cunningham, Friend & Nicholson (1963) in pigs. Sineshchekov and his colleagues (Sineshchekov, 1953(Sineshchekov, , 1962 have also used this approach to a wide variety of problems in sheep, cattle, pigs and horses. METHODSSheep. Two Scottish Blackface sheep were used: Alfred, a 2-year-old wether weighing about 32 kg, and Clara, a 2-year-old ewe weighing about 43 kg. They were housed in rooms at a constant temperature (180 C) and illumination (12 hr daily).At operation for insertion of the ileal cannulae the sheep were anaesthetized with pentobarbitone sodium and the ileum was divided 5-10 cm from the ileo-caecal junction. The cut ends were closed and a moulded plastic cannula with an internal diameter of 11 mm (Ash, 1962) was sewn into the side of each stump. The cannulae were exteriorized through stab wounds in the abdominal wall and were joined by glass or Perspex tubing to re-establish

1. An experiment was conducted using three non-lactating cows completely maintained by infusions of volatile fatty acids into the rumen, and casein into the abomasum. Plasma insulin responses to propionic acid, glucose or casein were recorded. Further information was obtained using protein-free infusions.2. When part of the propionic acid was infused into the rumen in a twice-daily 3 h dose and the remainder infused continuously with acetic and butyric acids and casein, there were large increases in the concentrations of propionic acid and insulin in the jugular blood. When glucose, corresponding in energy to that supplied by the intermittent propionic acid infusions was similarly infused, the plasma levels of glucose and insulin were increased. Glucose appeared to stimulate a greater increase in insulin than did propionic acid. Casein infused into the abomasum in intermittent doses produced a rise in plasma insulin, but smaller than that observed with propionic acid or with glucose.3. The protein-free infusion was characterized by a lower concentration of insulin in the blood plasma, a reduction in plasma urea and free amino nitrogen and unchanged plasma glucose.Glucose, volatile fatty acids (VFA) and amino acids (AA) are generally considered to be potential stimuli for insulin secretion in the ruminant. There are various reports of intravenous infusion of glucose or VFA having produced elevation in plasma insulin concentration (Manns & Boda, 1967; Horino et al. 1968). Similar rises were not observed when these nutrients were infused into the abomasum and rumen respectively, so as to ensure more normal absorption and metabolism (Sterm et al. 1970;Bassett, 1972).The present experiment was designed to measure plasma insulin and metabolites in cattle when glucose, propionic acid or casein were infused as intermittent doses or continuously into the rumen or abomasum. Information on metabolites in the blood plasma of ruminants maintained on protein-free diets is not easy to interpret, since protein of rumen microbial origin is still digested and absorbed in the small intestine. A study was made when the animals were maintained on a protein-free infusion. E X P E R I M E N T A L Animals and treatmentsThree non-lactating Friesian cows, each fitted with a rumen cannula and with an abomasal catheter, were used. Their initial and final average live weights were 517 and 576 kg respectively. They were infused as described by MacLeod et al. (1982). No solid food was offered. The infusion room temperature was maintained at approximately 22" and the level of infusion was calculated to be approximately 1.5 x maintenance energy from an estimated requirement of 0450 MJ/kg live per d. The cows were allocated to a randomized sequence of six treatment periods, each of 7 d duration. When increased amounts of VFA or different mixtures were required for consecutive treatments, the change was effected gradually over 2 d. Vtdnnaires, 45,

I . Two young steers, aged approximately 6 months and each fitted with a rumen and an abomasal cannula, were used to measure the flow of digesta to the abomasum over periods of 24 h. A diet of concentrates, at two levels, and a diet of hay cubes were given to the steers. Paper impregnated with chromium sesquioxide was inserted into the rumen twice daily.2. The amount of digesta passing to the abomasum and the output of faeces were measured and the values were adjusted to give 100% recovery of chromium sesquioxide. Measurements were also made of concentrations of plasma glucose, of volatile fatty acids (VFA) in both the rumen and abomasal fluid, and of rumen fluid volume and outflow.3. About 60-80 yo of the digestible dry matter and of the digestible energy of both diets disappeared from the forestomach (reticulo-rumen and omasum). The amounts of starch flowing through the abomasum differed little between diets and ranged from 29 to 77 g daily.4. The volume of rumen fluid did not differ consistently between diets, but the outflow of fluid from the rumen was considerably higher when hay was given. 5 . Diet had little influence on plasma glucose but affected the concentrations and molar proportions of VFA in the rumen fluid, and to a lesser extent in the abomasal fluid.Sheep fitted with cannulas into various parts of the digestive tract have been used by Topps, Kay & Goodall (1968) to show that about 9 j yo of the starch ingested as a concentrate diet was fermented in the rumen. Since some of the starch reaching the intestines may have been of microbial origin, degradative processes in the rumen are evidently very effective in breaking down dietary starch given at a high level. These observations in sheep led to speculation as to whether digestion in cattle receiving high-cereal diets followed the same pattern. Although it is well established that the digestive capabilities of cattle and sheep are very similar (Swift & Bratzler, 1959), anatomical differences, such as the size of the reticulo-omasal orifice, may cause different retention times in the rumen of certain parts of the diet and this might lead to differences in the extent to which they are degraded. Furthermore, a recent report by Karr, Little & Mitchell (1966) on work with yearling steers given high-maize diets indicated that large quantities of starch, as much as 38 yo of dietary intake, passed through the abomasum. Experiments were therefore carried out with two young steers fitted with rumen and abomasal cannulas in an attempt to obtain further evidence on this subject.