Substances in the calf alimentary tract interfering in the determination of polyethylene glycol

Estimation of rates of outflow of protein supplement from the rumen by determining the rate of excretion of chromium-treated protein supplements in faeces

An experiment was conducted to study the possibility of using marker concentration in faeces to estimate rumen outflow of Cr-treated protein supplements and the liquid phase (PEG). There were no significant differences in the outflow of each marker from the rumen when determined directly from rumen or indirectly from faeces, suggesting that faeces could be used to measure the outflow from the rumen without the need for surgical preparation of the animals. The outflow rate of the liquid phase was considerably faster than Cr-treated protein supplements.

Rates of Production of Acetate, Propionate, and Butyrate in the Rumen of Lactating Dairy Cows Given Normal and Low-Roughage Diets

Five lactating dairy cows with a permanent cannula in the rumen were given (kg DM/d) a normal diet (7.8 concentrates, 5.1 hay) or a low-roughage (LR) diet (11.5 concentrates, 1.2 hay) in two meals daily in a two-period crossover design. Milk fat (g/kg) was severely reduced on diet LR. To measure rates of production of individual volatile fatty acids (VFA) in the rumen, 0.5 mCi 1-(14)C-acetic acid, 2-(14)C-propionic acid, or 1-(14)C-n-butyric acid were infused into the rumen for 22 h at intervals of 2 to 6 d; rumen samples were taken over the last 12 h. To measure rumen volume, we infused Cr-EDTA into the rumen continuously, and polyethylene glycol was injected 2 h before the morning feed. Results were very variable, so volumes measured by rumen emptying were used instead. Net production of propionic acid more than doubled on LR, but acetate and butyrate production was only numerically lower. Net production rates pooled across both diets were significantly related to concentrations for each VFA. Molar proportions of net production were only slightly higher than molar proportions of concentrations for acetate and propionate but were lower for butyrate. The net energy value (MJ/d) of production of the three VFA increased from 89.5 on normal to 109.1 on LR, equivalent to 55 and 64% of digestible energy, respectively. Fully interchanging, three-pool models of VFA C fluxes are presented. It is concluded that net production rates of VFA can be measured in non-steady states without the need to measure rumen volumes.

Effects of nutrient solutions on concentration analysis of non-absorbable dilution markers--implications for studies of gastric emptying

Gastrointestinal luminal contents may interfere with concentration analysis of non-absorbable dyes. However, non-absorbable markers are broadly used for studies of gastric emptying rates of nutrient solutions. This prompted us to evaluate the properties of non-absorbable markers to mark such nutrient solutions. In vitro concentrations of polyethylene glycol, phenol red, dextran blue, two anthroquinone dyes and inulin were determined spectrophotometrically in the presence or absence of a formula diet, single compounds of the diet or an oligo-peptide diet, and the reproducibility and validity of the analyses were evaluated. The presence of the formula diet or the oligopeptide diet seriously impaired the analyses of marker concentrations, whereas single nutrient compounds did not uniformly interfere. The analysis of polyethylene glycol and phenol red concentrations was impaired by proteins, while the analysis of inulin concentration was impaired by carbohydrates. Dextran blue and the anthroquinones were completely eliminated by protein-precipitation procedures. In conclusion, phenol red and polyethylene glycol should only be used as marker substances for protein-free meals or nutrient solutions, while inulin should not be used with meals or nutrient solutions containing carbohydrates. Marker dilution techniques cannot be recommended for measurements of gastric emptying rates of complete meals.

Exchanges of magnesium and phosphorus at different sites in the ruminant stomach

Three ruminating calves were each provided with a rumen cannula (from which reticulum samples could be obtained), an abomasal cannula and a sleeve sutured at the omasal-abomasal orifice that permitted digesta flowing from the omasum to be diverted and collected. The calves were each given in turn a high roughage (HR) and high concentrate (HC) diet consisting mainly of dried grass and flaked maize in the proportions by weight of 3:2 and 1:2 respectively. A water soluble non-absorbable marker (polyethylene glycol) and a particulate marker (103Ru-phenanthroline complex) were also given and the diets were sometimes supplemented with MgSO4. For each diet (HR(O), HR(Mg), HC(O), HC(Mg)) samples were taken from the reticulum and omasal outflow. Magnesium, phosphorus, PEG and 103Ru were measured in the samples as taken and liquid-rich and solid-rich fractions prepared from them. From their distributions relative to the two markers, Mg and P flows into and out of the omasum were estimated. Results were too few to show significant differences in absorption efficiency between diets but overall approximately 10-40% of the Mg entering the omasum was absorbed as a net effect implying that this organ may be the major site of Mg absorption in young cattle. For P also substantial amounts entering the omasum (approximately 10-40%) were absorbed in that organ.

Exchanges of water and certain water-soluble minerals during passage of digesta through the stomach compartments of young ruminating bovines

1. Four ruminating bull calves were provided with cannulas in the rumen and abomasum and a sleeve sutured at the omosal-abomasal orifice that permitted digesta flowing from the omasum to be diverted and collected. 2. The calves were each given in turn a high-roughage (HR) and high-concentrate (HC) diet consisting mainly of dried grass and flaked maize in the proportions 3:2 and 1:2 by weight respectively. Water-soluble non-absorbable marker (polyethylene glycol) was also given and the diets were sometimes supplemented with magnesium sulphate. For each diet (HR(0), HR(Mg), HC(0), HC(Mg], collections were made from the rumen, reticulum, omasal outflow and abomasum, and flows of water, sodium, potassium and chloride calculated at these sites relative to intakes. 3. The general pattern of net exchange was similar for all the diets. Substantial additions of water and Na, a small addition of K and a small absorption of Cl occurred between mouth and reticulum. Substantial (approximately 40-60%) absorption of water and Na, a small absorption of K and considerable secretion of Cl occurred in the omasum. Quantitative comparisons indicated that addition of water and Na up to the reticulum, presumably in saliva, was significantly greater for the HR than the HC diets. Addition of Mg appeared to stimulate absorption of Na and water up to the reticulum for unknown reasons. Re-absorption of these components in the omasum varied for different calves and diets but appeared to be influenced primarily by a positive linear relation between amounts of digesta flowing into the omasum and amounts of water and Na absorbed from it. The proportion of water absorbed also increased with increasing entry rates of water. 4. Other findings showed that pH values rose slightly (about 0.2 pH units) but significantly in the reticulum compared with the rumen and that the value fell again by about the same amount during the passage of digesta through the omasum. Changes between omasal outflow and the abomasum were as expected, with marked additions of Cl, Na and water and a fall in pH.

Digestion, absorption and utilization of single-cell protein by the preruminant calf. Abomasal outflow and its composition from calves given milk-substitute diets containing varying amounts of either bacterial or yeast protein

Two experiments of Latin square design, with four Friesian bull calves fitted with re-entrant duodenal cannulas at 4-10 d of age, were made to study the effect of giving varying levels of single-cell protein on the abomasal outflow and composition of digesta. In Expt 1, diets in which 0, 220, 440, and 660 g/kg milk protein were replaced by the bacterial protein Pruteen were compared from 14 d of age. In Expt 2, which began at about 61 d of age, a comparison was made of diets in which 0, 220, 440 and 660 g/kg milk protein were replaced by the yeast protein Toprina. Collection of abomasal outflow was made for 8 h after feeding for 2 d within each 6 d period of the Latin square design experiment. The amount of diet offered daily was 50 g dry matter/kg body-weight 0.75. Polyethylene glycol (PEG), which was used as an indigestible marker, total nitrogen (TN), protein-N (PN), fat, and potassium, sodium and chloride ion outflows were measured together with pepsin (EC 3.4.23.1) and chymosin (EC 3.4.23.4) activities, pH and titratable acidity. In Expt 1 there was little difference in the outflow of liquid digesta between diets and about 0.9 of the dietary PEG was recovered within the 8 h collection period. With increasing amounts of Pruteen in the diet, outflows of TN, PN, fat and Na+ increased, and the pH of digesta increased. However, the volume of 'apparent secretion' into the abomasum (outflow - intake), pepsin activity, chymosin activity, titratable acidity, (outflow of Cl- -outflow of Na+) as a measure of outflow of HCl, and outflows of K+ and of Cl- were reduced. All outflows decreased with the time interval after feeding, except (Cl- -Na+) outflow. In Expt 2, the same trends as in Expt 1 were apparent, but since one calf had to be slaughtered and the experiment had to be analysed as a randomized block, only PN and K+ outflows and pH were significantly affected by dietary treatment, with K+ outflow increasing, rather than decreasing, with increasing concentration of single-cell protein in the diet.(ABSTRACT TRUNCATED AT 400 WORDS)

The nutritive value of rumen micro-organisms in ruminants. 2. The apparent digestibility and net utilization of microbial N for growing lambs

Four experiments were conducted with eighteen lambs sustained entirely by intragastric nutrition at gross energy inputs varying from 430 to 860 kJ/kg live weight0.75 (W0.75). Isolated rumen micro-organisms (RMO) were infused into the abomasum in quantities varying from 0 to 2 g digestible N/kg W0.75 to assess the increase in N balance as a result of increasing RMO input when N was limiting. The over-all utilization of N from RMO (RMO-N) could be described by the equation y = 0.543 X -0.457, residual SD = 0.037, where y is the N balance and X is the abomasal input of RMO-N, both expressed in g/kg W0.75. Thus the coefficient of efficiency of utilization of infused RMO-N was 0.543 (SE 0.008). The coefficient of efficiency of utilization of RMO-N truly digested (i.e. the biological value) was 0.659 (SE 0.015). The RMO-N input (mean with SE) at N equilibrium was 0.843 (0.009) g/kg W0.75. The true digestibility of RMO-N was 0.813 (0.004). The urinary N excretion when no N was infused was 0.329 (0.008) g/kg W0.75 and the N excreted via the faeces with zero N input was 0.036 (0.009) g/kg W0.75.

The nutritive value of rumen micro-organisms in ruminants. 3. The digestion of microbial amino and nucleic acids in, and losses of endogenous nitrogen from, the small intestine of sheep

An experiment was conducted with three sheep maintained entirely by intragastric nutrition to estimate the digestibility of isolated individual constituents and amino acids (AA) of rumen micro-organisms (RMO) in the small intestine. Five levels of RMO were infused into the abomasum. The apparent and true disappearance of the individual components were measured by regression of abomasal input on the passage at the ileum. The true digestibility values of N, AA-N, DNA and RNA were 0.82, 0.85, 0.81 and 0.87, respectively. The digestibility of individual AA varied between 0.80 and 0.88, the only exceptions being diaminopimelic acid (0.37), histidine (0.68) and cystine (0.73), which were significantly lower than the average (0.847). The endogenous components in the ileal fluid in sheep given protein-free infusions, expressed in mg/kg live weight0.75 per d, were total N 42 and AA-N 20.

Prediction of the suitability of soya-bean products for feeding to preruminant calves by an in-vitro immunochemical method

1. An immunochemical test for predicting the suitability of different soya-bean products for feeding to preruminant calves was studied. Calves fitted with abomasal and re-entrant ileal cannulas, were first given a series of feeds containing heated soya-bean flour and two with casein as the protein source, and then given further test feeds in which different experimental soya-bean products, prepared under conditions which might be used commercially, provided the nitrogren source. These products (Q, R, S and T) were prepared respectively by extracting fat-free soya-bean flour with aqueous ethanol at 960, 650, 650 and 550 ml/l and at 60, 60, 78 and 78° and then treating the residue with steam for 30 min.

2. After infusion of a test feed into the abmasum measurements were made of transit time through the small intestine, flow-rate of ileal digesta, recovery of polyethylene glycol (a water-soluble marker added to the feed) and net N absorption up to the distal ileum. Glycinin and β-conglycinin, antigenic constituents of soya-bean protein, were determined in saline (9 g sodium chloride/l) extracts of soya-bean products by haemagglutination inhibition assay.

3. After calves had been given a series of four feeds containing heated soya-bean flour, they showed hypersensitivity to the flour by developing disturbances in digesta movement and N uptake. When experiments were made to compare the effects of giving feeds based on casein with those containing products R, S and T it was shown that some differences in transit times and flow-rates of digesta through, and N absorption from, the small intestine occurred. Disturbances were, however, much less than those observed with product Q feeds.

4. Haemaggultination inhibition assay of products Q, R, S and T gave titres (log2 reciprocal of highest dilution of saline extract inhibiting agglutination) of 12, 5, 3 and 2 for glycinin and 13, 3, 3 and 2 for β-conglycinin respectively. After steam treatment only product Q gave measurable titres; 10 and 11 for glycinin and β-conglycinin respectively.

5. It is concluded that the haemagglutination inhibition assay is a suitable in vitro method of indicating whether soya-bean products given in liquid feeds to preruminant calves will cause gastrointestinal allergic reactions. Furthermore, results show that the removal of deleterious factors from soya-bean meal by treating with ethanol, is critically dependent on the proportion of water present in the ethanol and the temperature of the treatment.

The uptake of nutrients from the small intestine of gnotobiotic and conventional chicks

1. Uptake of L-[2(n)-3H]methionine and 3-O-methyl[14C]-D-glucose (3MG) from jejunal loops in vivo was investigated in germ-free (GF), gnotobiotic (GN) and conventional (CV) chicks aged between 2 and 4 weeks. 2. Body-weight gain was less, and intestine weight per unit length greater, in CV and GN birds than in corresponding GF birds. 3. Uptake of both nutrients was less in CV and GN birds when calculated per g intestinal tissue, but no difference was found between any of the groups when uptake was expressed per unit length of intestine. 4. Concentration of methionine in mesenteric and cardiac blood was higher, and amounts in the intestinal wall lower, in CV chicks than in corresponding samples from GF birds. 5. Concentration of 3MG in mesenteric blood was similar in both environments but it was higher in cardiac blood and lower in the gut wall of CV birds. 6. It was concluded that uptake of methionine and glucose is not impaired by the presence of micro-organisms in the gut.

Artificial rearing of pigs. 10. Effect of replacing dried skim-milk by a single-cell protein (Pruteen) on performance and digestion of protein

1. Spray-dried diets were prepared containing (g/kg): dried skim-milk 665, dried whey 65, soya-bean oil 270 (diet U); or single-cell protein (Pruteen; SCP) 308, dried whey 440, soya-bean oil 252 (diet X). The diets had a crude protein (nitrogen × 6·25) content (g/kg) of 250 (diet U) and 240 (diet X), excluding nucleic acids (36 g/kg) in diet X.

2. The diets were reconstituted (200 g dry matter/l) and mixtures of diets U and X prepared to give diets supplying 0 (diet U), and approximately 400 (diet V), 600 (diet W) and 800 (diet X) g crude protein from SCP/kg total protein. All diets were supplemented with vitamins, and minerals to equalize the calcium, phosphorous, sodium and potassium concentrations.

3. Pigs weaned at 2 d of age were given the diets at hourly intervals on a scale based on live weight. At 28 d age the experiment was terminated and pigs killed 1 h after a feed for a study of protein digestion. Polyethylene glycol (PEG) was fed in the diets (0.5 g/l) for 24 h before slaughter.

4. Performance of pigs fed on diet V was as good as on the all-milk diet U. Greater levels of replacement by SCP (diets W and X) reduced performance. Mortality was greater on the all-milk diet, but protein source had no effect on the incidence of scouring. N retention (g/d per kg live weight) was similar for all diets but declined with age.

5. SCP appeared to stimulate secretion of pepsin and chymotrypsin, and reduced the pH value in digesta in the stomach. Enzyme adaptation may have been insufficient to digest high levels of SCP in the diet, and together with the decreased transit time observed using PEG as a marker, may account for the poorer performance when 600 or 800 g/kg milk protein was replaced.

6. Nucleic acids from SCP were metabolized and not retained for tissue synthesis. Allantoin excretion accounted for 75% of the theoretical maximum for complete excretion of nucleic acids, and uric acid excretion was also increased.

The effect of giving feeds containing soya-bean meal treated or extracted with ethanol on digestive processes in the preruminant calf

1. Preruminant calves, fitted with abomasal and re-entrant ileal cannulas, were given, at intervals of 2–3 d by infusion into the absomasum, a series of five single experimental feeds containing heated soyabean flour (product B) as the only protein source. The calves were sensitized in this way to a constituent in the soya beans and by the fifth feed showed a number of digestive disturbances. Further test feeds were then given in which heated soya-bean flour was sometimes replaced by soya-bean products prepared under laboratory or commercial conditions by treating I part fat-free raw soya-bean meal with either I part (product M) or 4 parts (product L) ethanol (750 ml/l) at 78–80° and evaporating the whole mixture to dryness, or by extracting I part meal with 4 parts aqueous ethanol under similar conditions (product K). Products M, L and K were heated with steam and finely ground. Feeds prepared from casein and from commerical ethanol-extracted concentrate (product D) were also examined.

2. Measurements were made of transit time through the small intestine, flow rate of ileal digesta, recovery of polyethylene glycol (a water-soluble marker added to the feed) and net nitrogen absorption up to the distal ileum. Compared to feeds based on casein, feeds containing products K, L or M showed some differences in digesta movement and N uptake, but much less disturbance than feeds containing product B. Products prepared by extracting soya-bean meal with ethanol appeared to be slightly superior to those prepared from meal treated with ethanol, but the differences were not significant.

3. Weanling rats were used to assess the nutritive value of soya-bean products by an N balance method. Digestibilities (mean 0.948) and biological values (mean 0.860) obtained for products B, D, K and L did not differ significantly.

4. Results confirmed that extracting soya-bean meal with hot aqueous ethanol improved its value for calf feeding and indicated that at least part of the effect was due to the destruction of a toxic constituent present in the soya bean which probably acted by inducing a gastrointestinal allergy.

The effect of different diets including those containing soya-bean products, on digesta movement and water and nitrogen absorption in the small intestine of the pre-ruminant calf

1. Preruminant calves, fistulated in the abomassum and distal ileum, were given by infusion into the abomasum, at intervals of 2-3 d, single experimental feeds of cow's milk or a synthetic milk diet in which the protein source was casein or a soya-bean product. Polyethylene glycol (PEG) and phenol red were included as markers. 2. After infusion of the experimental feed, measurements were made of transit time from proximal duodenum to distal ileum and mean ileal flow-rates for the first 3 and 21 h after food residues reached the distal ileum. PEG recoveries for these two periods and net nitrogen absorption up to the distal ileum were also determined. In some experiments sodium, potassium and magnesium concentrations and numbers of viable bacteria in ileal digesta were determined. 3. Measurements of passage of digesta, recovery of marker and net N absorption did not differ greatly between calves given cow's milk and the synthetic milk diet containing casein. Compared to the casein-based diet, a diet based on heated soya-bean flour given to a calf for the first or second time produced a somewhat higher ileal flow-rate and a significantly lower net N absorption. Net N absorption was even lower when a calf received a diet containing unheated soya-bean flour. 4. Calves given the diet containing heated soya-bean flour on several occasions appeared to develop a sensitivity to the flour, and after further feeds containing it they had significantly higher rates of ileal flow (accompanied by correspondingly high rates of Na and K flow), lower small intestine transit times and lower net N absorption values than similarly fed unsensitized calves. They also had significantly lower rates of passage of marker in the first few hours after food residues reached the ileum, indicating inhibition of abomasal emptying. Over all, the changes indicated a severe disturbance in digestive function which was not caused by abnormal bacterial growth and may have been due to a gastrointestinal allergy. 5. Diets prepared from water-extracted flour and from soya-bean-protein isolate also led to digestive disturbances in sensitized calves, but those containing concentrates prepared by extracting soya-bean meal with hot aqueous ethanol did not.

Absorption of L-histidine and glucose from the jejunum segment of the pig and its diurnal fluctuation

1. Flow rate of digesta and its component in the upper jejunum, and the absorption of L-histidine and glucose from the jejunum segment were measured in pigs fitted with three simple cannulas. The pigs were fed once faily at 08.30 hours. 2. Maximum flow of digesta was obtained in the period 10.00-10.30 hours; the flow rate decreased with time after feeding, reaching a minimum in the period 22.00-22.30 hours. 3. The absorption rate for L-histidine and glucose increased in a hyperbolic manner with increasing concentrations of infused test material, which ranged from 2.5 to 20 g/1 for each material. 4. L-histidine and glucose were absorbed nearly independently when perfused in combination. The absorption rates for glucose were significantly (P less than 0.01) greater than the corresponding rates for L-histidine at each concentration of infusate. 5. The absorption of both L-histidine and glucose expressed as a percentage of the amounts in the perfusate decreased with increasing flow rate of perfusate, from 400 to 800 ml/h. The increase in flow rate from 400 to 800 ml/h was associated with a 20% increase in L-histidine absorption rate; there was a 30% increased in glucose absorption rate when the flow rate was increased to 600 ml/h, but no further incrase at 800 ml/h. 6. The absorption of both L-histidine and glucose decreased with time after feeding; the absorption rates for L-histidine and glucose measured for the period 10.00-22-30 hours were 126 and 133%, respectively, of those measured for the period 22.00-22.30 hours.

The effect of different feeds, including those containing soya-bean products, on the passage of digesta from the abomasum of the preruminant calf

1. The effects of various factors on rates of flow and composition of digesta leaving the abomasum of preruminant calves were studied. The possible relation of some of these effects to the development of serum antibodies to certain dietary constituents has also been examined. Two situations were distinguished: (a) unsensitized responses, shown by calves receiving milk protein or soya-bean products for the first one or two occasions; (b) sensitized responses, shown by calves receiving certain soya-bean products, after a number of these feeds had been given. 2. For unsensitized calves, the rate of flow of total digesta from the abomasum was greater in the first few hours after a feed consisting of a mineral solution was given, than after cow's milk was given. This difference wasapparently due to differences in the composition of digesta entering the duodenum. Total digesta flows after giving synthetic milk feeds, prepared from different protein sources, were similar to those after cow's milk was given. 3. For sensitized calves, rates of flow of total digesta from the abomasum were greatly affected by the nature of the protein source used in the diet. Soya-bean flour (heated or unheated) generally caused inhibition of flow for some hours after feeding; a soya-bean protein isolate (isoelectric) had a similar but smaller effect, but a soya-bean concentrate (prepared by alcohol extraction of a soya-bean flour) and milk protein had little or no effect. The inhibition, believed to be a sign of more general disorders, appeared to be caused by a factor entering the duodenum which induced a change in the way in which the calf responded, probably as the result of a gastrointestinal allergy. 4. Calves given soya-bean flour or a soya-bean protein isolate (isoelectric) in their diets for several weeks, showed respectively high and low titres of serum antibodies to an antigen prepared from soya-bean flour. Calves given alcohol-extracted soya-bean concentrate had no similar antibodies. 5. In addition to variations in total digesta flow, dietary nitrogen compounds were held up in the abomasum to different extents after different feeds. After a whole-milk feed or a synthetic feed prepared from casein, a slow, steady release of N occurred over at least 9 h. N hold-up after giving soya-bean-containing feeds was slight for the soya-bean flour, but extremely marked for the soya-bean protein isolate (isoelectric). The latter hold-up was followed after several hours by a rapid outflow of N from the abomasum.

Absorption and catabolism of histamine in sheep

1. The fate of dietary histamine in sheep has been studied. When 200 mg histamine diphosphate was administered into a rumen with normal contents the average time taken for the biological activity to disappear from the rumen was about 4 hr. In sheep starved for 60 hr the activity disappeared much more slowly.2. When 0.9% NaCl solution was substituted for the normal rumen contents and the rumen was isolated in situ under anaesthesia, the disappearance of histamine was scarcely detectable. About 1% of the radioactivity introduced into such rumen preparations as [(14)C]histamine was recovered in the urine during a 6 hr period.3. When both [(14)C]histamine and 200 mg unlabelled histamine diphosphate were administered into the rumen, between 4 and 15% of the radioactivity and 2 and 11% of the biological activity reached the duodenum.4. When jejunal loops isolated between two pairs of re-entrant cannulas were perfused with 0.9% NaCl solution containing histamine a considerable fraction of the histamine was absorbed from the loops.5. When [(14)C]histamine and 200 mg histamine diphosphate were administered into the rumen an average of 9% of the radioactivity appeared in the urine. When histamine was given into the abomasum the corresponding figure in a single experiment was 25%.6. Between 11 and 34% of the radioactivity administered into the rumen as [(14)C]histamine was exhaled as (14)CO(2). Most of the (14)CO(2) seemed to stem from metabolism of [(14)C]histamine in the ruminoreticulum whereas the contribution of the intestines to (14)CO(2) was very small.7. When [(3)H]histamine was administered into the rumen most of the radioactivity in the urine a few days after administration was in the form of tritiated water. The formation of (3)H(2)O is probably a result of histamine metabolism in the fore-stomach, analogous to the formation of (14)CO(2).

Digestion and absorption of starch, maltose and lactose by the preruminant calf

1. Preruminant calves, some of which were equipped with re-entrant cannulas in the small intestine, were given liquid feeds in which various starches, maltose or lactose formed the sole source of carbohydrate.

2. The sugars left the abomasum at the same rate as a water-soluble marker but the starches were greatly delayed. Little starch left the abomasum until about 5 h after feeding. Examination of abomasal contents 0.5 h after feeding showed the starch to be associated with the casein clot.

3. Amounts of starch, maltose and lactose removed during the passage of digesta through the small intestine were about 60, 43 and 97% of intake respectively, with no marked difference with age between about 7 and 16 weeks.

4. No change in blood glucose was apparent in calves given starch-containing feeds. The possible effect of the retention of dietary starch in the abomasum in minimizing blood glucose responses is discussed.

Concurrent studies of the flow of digesta in the duodenum and of exocrine pancreatic secretion of calves. 2. The effects of addition of fat to skim milk and of 'severe' preheating treatment of spray-dried skim-milk powder

1. The duodenal flow of digesta and the concurrent pancreatic secretion were compared when six Ayrshire calves, with duodenal re-entrant and pancreatic sac cannulas, were fed on three reconstituted milks. The diets were: reconstituted, ‘mildly’ preheated, spray-dried skim-milk powder (SK); the same skim milk containing 20 g fat/l (SKF); and reconstituted, ‘severely’ preheated skim-milk powder containing 20 g fat/l (HSKF). The calves were fed ad lib. from teats twice daily from 9 to 21 d of age, each diet being offered for 4 d. Collections of duodenal digesta and pancreatic secretions were made for 12 h after the fourth and eighth meals on each diet.

2. The calves tended to have the highest liquid intakes when diet SK was given. After adjustment for differences in intake, diet SK resulted in the appearance of more hydrogen, chloride and potassium ions but less undigested protein nitrogen in the duodenal digesta than with either diet SKF or HSKF.

3. Compared with diets SK and SKF, the whey fluids from diet HSKF took significantly longer to leave the abomasum, less H+ passed through the duodenum during the first 6 h after feeding and less Cl− during the whole postprandial period. More undigested protein N and fat from diet HSKF passed through the duodenum during the first 6 h after feeding, although this difference was significant only for protein N during the 1st hour after feeding.

4. Over the 12 h postprandial period, the duodenal digesta contained almost exactly the same quantities of polyethylene glycol (PEG), N and fat as those in the meal. The total volume of digesta was 2.25 l greater than the quantity of milk ingested. When the hourly duodenal flows of PEG and fluid were expressed as the square root of the hourly quantities recovered, the pattern of abomasal emptying was rectilinear. The flows of N and fat were curvilinear, when expressed on the same basis.

5. The concentration of ‘sodium-free’chloride in the duodenal digesta, in excess of that ingested in the milk, was used as an indicator of the quantity of acid secreted by the abomasum. The relative quantity of acid secreted was greatest with diet SK and least with diet HSKF.

6. The pancreatic secretion of fluid was highest during the period 5–9 h after feeding but the secretion of enzyme activity was highest during the first 2 h after feeding.

7. Considerable variability in the secretion of enzyme activity was observed and the rate of secretion did not appear to be related to any component of the duodenal digesta.

8. Diet SKF was associated with a greater volume of pancreatic secretion and more pancreatic protease secretion than either diet SK or HSKF, but most amylase activity was secreted when diet HSKF was given. Evidence is presented which suggests that pancreatic enzyme activity adaptation occurred when diet HSKF was offered in succession to diet SK or SKF. The secretion of trypsin activity did not differ between diets.

Absorption of glucose and galactose and digestion and absorption of lactose by the prepruminant calf

1. Uptakes of glucose, galactose, glucose+galactose and lactose from the intestine were studied in preruminant calves fitted with cannulas in the proximal small intestine, and in slaughtered calves. Responses in concentration of blood sugar to the presence of sugar in the small intestine were also investigated.

2. Glucose and galactose were absorbed at about the same rate when present in the intestine separately. The rate for each sugar approached a maximum with increasing sugar concentration in the lumen.

3. When glucose and galactose were present in the intestine together, the rate of galactose absorption was greatly depressed; that of glucose was virtually unaffected. Consequently, when calves were fed with mixtures of glucose and galactose, absorption of galactose in the proximal intestine, where the relative concentration of glucose was high, was depressed. In the more distal intestine where the glucose concentration had fallen, absorption of galactose was rapid. Both sugars were absorbed efficiently during their passage through the whole small intestine, but at different sites.

4. Galactose appeared in the blood after galactose alone was given but conversion of some galactose into glucose always occurred. Results of experiments in which [14C]galactose, together with glucose, was infused into the duodenum of a calf suggested that under these conditions the rate of galactose absorption was depressed to such an extent that nearly all the galactose entering the blood was converted into glucose.

5. Lactose hydrolysis occurred much more rapidly than the absorption of its constituent monosaccharides. Thus, after lactose was fed to the calves, glucose and galactose accumulated in the lumen of the proximal small intestine. A similar accumulation occurred when lactose was infused into loops of small intestine. The rate-limiting step in the total absorption of lactose in the young calf was not, therefore, the hydrolysis stage, as reported for other mammals. The absorption of the released glucose and galactose occurred in a manner similar to that described above for mixtures of glucose and galactose.

Protein requirements of growing lambs

1. The protein requirements of lambs were established by measuring nitrogen balance in seventy-four animals given liquid diets which passed direct to the abomasum. Four groups of lambs weighing approximately 8 kg (group 1), 13 kg (group 2), 21 kg (group 3) and 30 kg (group 4) received diets in which 0·10, 0·15, 0·20, 0·25, 0·30, 0·35 or 0·40 of the digestible energy was provided as protein (DPE:DE ratio) and a gross energy intake of from 1·30 to 1·42 MJ/kg0·73per d.

2. When the protein requirements were taken to correspond to the protein intake at the point of intersection of the line describing the increase in N balance with increase in protein intake and the line representing the maximum N balance, values of 0·25, 0·23, 0·17 and 0·12 DPE:DE ratio were obtained for groups 1–4 respectively. The requirements expressed in these terms can be applied only to lambs fed on liquid diets which contain milk proteins and escape fermentation in the rumen. To enable the results to be applied to lambs given other diets, the requirements were expressed as g reference-protein (defined as a theoretical protein with the ideal pattern of amino acids) per MJ net energy and were 11·6, 10·4, 8·0 and 6·2 for groups 1–4 respectively. The relationship between protein requirement (Y, g reference protein/MJ net energy) and live weight (X, kg) was:Y= 13·4–0·242X.

3. The influence of energy intake on protein requirements in lambs is discussed and it is concluded that the results obtained are applicable to lambs given a metabolizable energy intake of more than about 1·75 times their maintenance requirement.

4. Application of the estimated requirements to ruminant lambs and methods of formulating diets to supply the required quantity of reference protein/MJ net energy are discussed.

EFFECTS OF NEUTRALIZING ACID WHEY POWDER IN MILK REPLACERS CONTAINING MILK AND SOYBEAN PROTEINS ON PERFORMANCE AND ABOMASAL AND INTESTINAL DIGESTION IN CALVES

Milk replacers with relatively low pH result from the inclusion of acid whey powder in the formula. Experiments were carried out to determine the effects of adjusting the pH of milk replacers containing different levels of acid whey and milk (M) or milk and soybean proteins (MS) on calf performance. Weight gains of calves to 8 weeks of age were increased by 15% (P < 0.20) in two experiments when the pH of the M diet with 23% whey powder was adjusted from about 5.7 to 6.8 with NaOH. Digestible nutrient intakes per unit weight gain decreased by about 15% (P < 0.10), but digestion coefficients were not significantly affected. Results from four calves with abomasal or reentrant intestinal cannulas indicated that the beneficial response to pH adjustment was due to a slower rate of abomasal emptying. Compared with the unadjusted diets, pH adjustment resulted in a greater drop in pH and higher nitrogen content (mg/ml) in abomasal digesta, and reduced volume flow, nitrogen, trypsin, and chymotrypsin in intestinal digesta. The calf responses to pH adjustment were less with the MS compared with the M diets containing 23% whey powder. Adjusting the pH of the M diet containing 52% acid whey powder from 5 to 6.8 had no effect on calf growth or nutrient utilization. The nitrogen supplied by the whey powder was calculated to be only 50% digestible by calves at 3–4 weeks of age. Proteolytic enzyme secretion from the pancreas was about 2.5 times less on the 52% compared with the 23% whey formula. We conclude that acid whey powder can be added to milk replacers at levels of about 23 % and that adjusting the pH improves calf performance.

The passage of calcium and strontium across the gut of the anaesthetized goat

1. The translocation of calcium and strontium across the intestine of the anaesthetized goat has been studied. It has been found to be unaffected by ouabain, by the absence of sodium, by a severely hypertonic environment and by heparin and chondroitin sulphate. Thus it is unlikely that, in the intact goat, the trans-mucosal sodium and calcium transport systems are interrelated.2. The effect of sodium alginate both on the rate of absorption and the calcium/strontium discrimination ratio has been confirmed.3. The movement of calcium ion in both directions across the intestinal mucosa has been studied and evidence for the active transport of calcium adduced.

Nucleic acid metabolism in the ruminant. 3. Amounts of nucleic acids and total and ammonia nitrogen in digesta from the rumen, duodenum and ileum of calves

1. Concentrations of nucleic acid nitrogen and other nitrogenous constituents were estimated in digesta taken from the proximal duodenum of calves which were given, either, one of a number of stall diets or pasture. These concentrations were compared, using polyethylene glycol (PEG) as a non-absorbed marker, with corresponding concentrations in rumen fluid and ileal contents.

2. There was little net change in amounts of RNA or DNA between rumen and duodenum relative to PEG, but there was a marked increase in amounts of total-N. In duodenal digesta, for any one animal given most diets, nucleic acid-N formed a fairly constant percentage (8–11 for different animals) of the total non-ammonia-N. This value was lower (by about 3) than the corresponding percentage in rumen fluid. Comparison of nucleic acid-N: total-N ratios in duodenal contents and bacteria suggested that, for these diets, about 40–55% of the non-ammonia-N in duodenal contents was of microbial origin.

3. During passage of digesta between the duodenum and ileum the mean percentage disappearances of total-N, RNA and DNA were estimated to be about 67, 85 and 75 respectively. There was evidence that these values varied with the amounts of the constituents entering the duodenum.

4. Ammonia was absorbed in the omasum-abomasum only when concentrations in rumen fluid were high (40 mM), but even moderate concentrations of ammonia entering the duodenum (3 mM) were efficiently absorbed (about 90%) in the small intestine.

Artificial rearing of pigs. 2. The time course of milk protein digestion and proteolytic enzyme secretion in the 28-day-old pig

1. The time course of digestion of milk protein was studied in the 28-d-old pig given a test meal of homogenized cow's milk after a preliminary starvation period.

2. The milk was found to clot in the stomach 15–30 min after the meal. The soluble or ‘whey’ fraction of the stomach contents rapidly passed into the small intestine. Most of the clotted digesta had also left the stomach z h after the meal.

3. The distribution of digesta was studied in six equal segments of the small intestine. In general, there were no significant increases in the amount of intestinal contents at any time after the meal when compared with those in starved pigs, suggesting that digestion of milk at this age is a very efficient process.

4. Fractionation of the soluble digesta from the stomach and small intestine in Sephadex G-25 indicated that relatively little proteolysis occurred in the stomach, but in the small intestine digestion proceeded rapidly, producing a considerable increase in free amino acids in the mid-region.

5. The level of proteolytic enzyme activity in the stomach wall was elevated at 15 min after the meal, but thereafter returned rapidly to the prefeeding levels. Increasing the level of feeding increased the enzyme activity of the digesta and stomach wall. The enzyme activity appeared to be mainly adsorbed by the stomach clot.

6. The proteolytic enzyme activity in the pancreas was unaffected by the meal. However, the activity in the contents of the small intestine increased after the meal, reaching a maximum value at 45 min. Some accumulation of enzymes was found in the lower part of the small intestine, except in the region of the distal ileum where a marked decline in enzyme activity occurred. Increasing the level of feeding increased the proteolytic enzyme activity in the contents of the small intestine.

7. The soluble marker polyethylene glycol was not entirely satisfactory as an indicator of the rate of passage of digesta. The concentration of the marker was found to be greater in the soluble stomach fraction than in the clot shortly after the milk had been ingested. The transit time of the marker from ingestion to the terminal ileum was 2–3 h.

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

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.

Dietary factors influencing the digestion of starch in the rumen and small and large intestine of early weaned lambs

1. Lambs fitted with cannulas in the abomasum, terminal ileum and caecum were used to study the digestion of starch and dry matter when rations with high starch content were given. Polyethylene glycol was used as an indigestible reference substance.

2. In Expt I reduction in level of feeding from an estimated adlib. intake to 70% of this level reduced the amount of dietary starch escaping fermentation in the rumen from 6.8 to 4.4% of intake on a barley diet and from 12.8 to 7.7% on a diet consisting of 40% dried grass and 60 yo barley. Inclusion of 40% chopped dried grass in the diet increased the amount of dietary starch escaping fermentation in the rumen. There appeared to be a linear relationship between the concentrations of starch in abornasal and ilcal dry matter, indicating a limited capacity for starch digestion in the small intestine.

3. In Expt 2 a barley diet was compared with diets based on flaked maize, ground maize or cracked maize. With these diets the percentage of dietary starch escaping fermentation in the rumen was respectively 6.2, 5.4, 12.1 and 142, showing that more starch escapes fermentation with uncooked maize diets than with barley diets.

4. The molar proportions of volatile fatty acids produced by fermentation in the caecum were apparently influenced by the amount of starch passing to the intestines. The highest proportion of acetic acid (78%) was associated with 4.5% of starch in abomasal dry matter, and the lowest proportion (57%)was associated with 20.1% of starch in abomasal dry matter.

5. The possible relationships between the extent of fermentation in the rumen and energy and nitrogen metabolism are discussed.

The absorption of long-chain fatty acids from the small intestine of the sheep

1. Three sheep, each of which was fitted with a rumen cannula and with two pairs of reentrant cannulas in different parts of the small intestine, were used in this study. They were fed on dried grass cubes or hay plus linseed meal and oats: an aqueous solution of polyethylene glycol (PEG) was infused continuously into the rumen.

2. Total lipids were extracted from samples of the chyme entering and leaving the different lengths of the small intestine embraced by the respective cannulas. The lipids were fractionated into unesterified fatty acids, neutral lipids and phospholipids and the contribution of each fraction to the total fatty acids was determined. The samples were also analysed for their PEG content, thus affording an index of the extent to which water had been absorbed from each particular length of intestine.

3. From the above findings and a knowledge of the flow-rate of the digesta, the uptake of unesterified fatty acids and the degree of dissimilation or uptake, or of both, of esterified fatty acids was calculated.

4. The results indicated that, by the time the digesta reached the ileum (i.e. the distal half of the small intestine), the uptake of fatty acids was almost complete, as was also the hydrolytic release of esterified fatty acids.

5. Though there were no gross differences in the overall composition of the unesterified and esterified fatty acids in different parts of the small intestine, it appeared that C18mono-unsaturated acid, the principal unsaturated unesterified acid, was absorbed somewhat more efficiently than were the major saturated acids (palmitic acid and stearic acid).