PASSAGE OF DIGESTA THROUGH THE CALF ABOMASUM AND SMALL INTESTINE

Biogeographical Differences in the Influence of Maternal Microbial Sources on the Early Successional Development of the Bovine Neonatal Gastrointestinal tract

The impact of maternal microbial influences on the early choreography of the neonatal calf microbiome were investigated. Luminal content and mucosal scraping samples were collected from ten locations in the calf gastrointestinal tract (GIT) over the first 21 days of life, along with postpartum maternal colostrum, udder skin, and vaginal scrapings. Microbiota were found to vary by anatomical location, between the lumen and mucosa at each GIT location, and differentially enriched for maternal vaginal, skin, and colostral microbiota. Most calf sample sites exhibited a gradual increase in α-diversity over the 21 days beginning the first few days after birth. The relative abundance of Firmicutes was greater in the proximal GIT, while Bacteroidetes were greater in the distal GIT. Proteobacteria exhibited greater relative abundances in mucosal scrapings relative to luminal content. Forty-six percent of calf luminal microbes and 41% of mucosal microbes were observed in at-least one maternal source, with the majority being shared with microbes on the skin of the udder. The vaginal microbiota were found to harbor and uniquely share many common and well-described fibrolytic rumen bacteria, as well as methanogenic archaea, potentially indicating a role for the vagina in populating the developing rumen and reticulum with microbes important to the nutrition of the adult animal.

Effect of suckling isotonic or hypertonic solutions of sodium bicarbonate or glucose on abomasal emptying rate in calves

OBJECTIVE

To determine and compare the abomasal emptying rates in calves suckling milk replacer or an isotonic or hypertonic solution of NaHCO(3) or glucose.

ANIMALS

5 male Holstein-Friesian calves that were < 30 days of age.

PROCEDURES

Calves were fed 2 L of milk replacer or isotonic (300 mOsm/L) or hypertonic (600 mOsm/L) solutions of NaHCO(3) or glucose containing acetaminophen (50 mg/kg). Venous blood samples and transabdominal ultrasonographic abomasal dimensions were obtained periodically after feeding, and abomasal luminal pH was continuously monitored by placement of a luminal pH electrode through an abomasal cannula. Abomasal emptying rate was assessed by the time to maximal plasma acetaminophen concentration, ultrasonographic determination of the half-time of abomasal emptying, and the time for luminal pH to return to within 1 pH unit of the preprandial value.

RESULTS

Hypertonic NaHCO(3) solution was emptied slower than an isotonic NaHCO(3) solution, isotonic glucose solution was emptied slower than an isotonic NaHCO(3) solution, and hypertonic glucose solution emptied slower than an isotonic glucose solution.

CONCLUSIONS AND CLINICAL RELEVANCE

An electrolyte solution for oral administration with a high osmolarity and glucose concentration may lead to a slower resuscitation of dehydrated diarrheic calves because such solutions decrease the abomasal emptying rate and therefore the rate of solution delivery to the small intestine. Whether slowing of the abomasal emptying rate in dehydrated diarrheic calves suckling an oral electrolyte solution is clinically important remains to be determined.

Assessment of the effects of erythromycin, neostigmine, and metoclopramide on abomasal motility and emptying rate in calves

OBJECTIVE

To determine and compare the effects of erythromycin, neostigmine, and metoclopramide on abomasal motility and emptying rate in suckling calves.

ANIMALS

6 male Holstein calves (15 to 40 days of age).

PROCEDURE

Calves were monitored for 1 hour before being fed milk replacer (60 mL/kg; time, 0 minutes) and then were monitored for another 3 hours. Calves received 6 treatments in randomized order: erythromycin (8.8 mg/kg, IM) at -30 minutes; low-dose erythromycin (0.88 mg/kg, IM) at -30 minutes; erythromycin (8.8 mg/kg, IM) at -30 minutes and neostigmine (0.02 mg/kg, SC) at -30 and 90 minutes; neostigmine (0.02 mg/kg, SC) at -30 and 90 minutes; metoclopramide (0.1 mg/kg, IM) at-30 and 90 minutes; and placebo (2 mL of saline [0.9% NaCl] solution, SC) at -30 minutes. Abomasal volume was calculated from ultrasonographic measurements of abomasal width, length, and height. Abomasal motility and emptying rate were assessed by measuring luminal pressure and change in abomasal volume over time.

RESULTS

Administration of erythromycin (8.8 mg/kg) increased the frequency of abomasal luminal pressure waves and the mean abomasal luminal pressure and decreased the half-time of abomasal emptying by 37%. Administration of metoclopramide, neostigmine, and low-dose erythromycin (0.88 mg/kg) did not alter abomasal motility, mean luminal pressure, or emptying rate.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that administration of erythromycin at the labeled antimicrobial dose (8.8 mg/kg, IM) exerted an immediate, marked prokinetic effect in healthy suckling calves, whereas administration of metoclopramide or neostigmine did not alter abomasal motility or emptying rate.

Effect of an orally administered antacid agent containing aluminum hydroxide and magnesium hydroxide on abomasal luminal pH in clinically normal milk-fed calves

OBJECTIVE

To determine the effects of a commercially available orally administered antacid agent containing aluminum hydroxide and magnesium hydroxide on abomasal luminal pH in clinically normal milk-fed calves.

DESIGN

Randomized trial.

ANIMALS

5 male dairy calves.

PROCEDURE

Throughout the study, calves were fed milk replacer at 7:30 AM and 7:30 PM. Cannulae for pH electrodes were placed in the abomasal body and pyloric antrum. Treatments consisted of oral administration of a high (50 ml) or low (25 ml) dose of the antacid agent and oral administration of milk replacer alone (control). Antacid was given at 7:30 AM, 3:30 PM, and 11:30 PM, and luminal pH was monitored continuously for 24 hours, beginning 15 minutes before administration of the first dose of antacid.

RESULTS

Administration of the first dose of antacid at the time of the morning feeding resulted in an increase in mean abomasal body luminal pH of < 1 pH unit, whereas administration of the second and third doses of the antacid caused transient (< 3 hours) increases in mean luminal pH of approximately 1.5 (low dose) and 2.5 (high dose) pH units.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that clinically normal milk-fed calves given a commercially available antacid agent, PO, will have a transient increase in abomasal luminal pH. Such agents may, therefore, have a role in the treatment of abomasal ulceration in calves; however, the long-term effects of orally administered antacid agents in milk-fed calves and the clinical efficacy of such agents in treating abomasal ulceration remain to be determined.

Mucosal uptake, mucosal transfer and retention of iron in veal calves

A method for studying iron absorption in humans was adapted to veal calves. Three 10-week-old calves with moderate (calves 1 and 2) or severe (calf 3) iron deficiency were given an abomasal injection of 59Fe and 51Cr and all their faeces were collected over 15 days in order to measure mucosal uptake, mucosal transfer and retention of iron. The mucosal uptake was 62.2, 53.4 and 71.8% in calves 1, 2 and 3, respectively. The iron retention measured 14 days after administration of the test dose was 57.4, 52.3 and 56.4% in calves 1, 2 and 3, respectively. Maximal plasma activity was found in all three calves between 1 1/2 and 2 h after injection of the test dose. The plasma activity decreased rapidly, with a slight increase between the 5th and the 10th hour. After 21 h, less than 0.25% of the injected dose was still present in 1 litre of plasma. Not all the 51Cr was recovered in the faeces. No 59Fe was found in the urine but some 51Cr could be detected. The results of this study show that the method described is useful for measuring the different steps of iron absorption in iron-deficient veal calves.

Effect of prolonged, continuous rectal distention on mouth-to-cecum and colonic transit time in pigs

The effect of prolonged (6 h), continuous rectal distention on mouth-to-cecum and colonic transit time was studied in four unrestrained pigs. Mouth-to-cecum transit time was determined from samples of cecal efflux using the phenol red dye technique. Colonic transit time was assessed with radiopaque markers that were injected into the cecum before each trial. Rectal distention was applied 2-1/2 h before feeding, during feeding, and 3-1/2 h after feeding. No distention was applied during control conditions. Stools were collected for 48 h after marker application. Rectal distention increased mouth-to-cecum transit time (p < 0.05). Colonic transit time was also prolonged by rectal distention as shown by a significant decrease in the number of markers excreted within 36 h (p < 0.05). Rectal distention for 6 h increased colonic transit time up to 30 h following distention and prolonged mouth-to-cecum transit of a high fat liquid meal.

The effect of age and diet on sulfadiazine/trimethoprim disposition following oral and subcutaneous administration to calves

Thirty milligrams per kilogram of sulfadiazine/trimethoprim (SDZ/TMP, Tribrissen) was given orally and subcutaneously (s.c.) to two groups of male, Holstein calves. One group was fed milk-replacer throughout the 13-week period of the study while the second group was weaned onto a chopped grain-fiber mixture when 5 weeks old. Serum and urine were assayed for concentrations of unchanged drug. Trimethoprim bioavailability, following oral administration at 1, 6 and 12 weeks of age, is higher in milk-fed calves (non-ruminants) than in grain-fiber-fed calves (ruminants); bioavailability decreases with increasing age in both groups of calves. Serum concentrations above 0.1 micrograms/ml (the level of sensitivity of the assay) could not be obtained in ruminating calves. The rate of SDZ absorption following oral administration, as determined by the Wagner-Nelson method, was very slow in all the calves in this study with average half-life values ranging from 8.2-12.67 h; absorption was slightly faster in ruminating calves. Absorption of SDZ is rate-limiting and determines the biological half-life of the drug; SDZ serum concentrations above 2 micrograms/ml were maintained in all calves for at least 24 h. Following s.c. administration of Tribrissen to 7-and 13-week-old calves, urinary excretion patterns indicated that TMP was slowly released from the injection site; serum concentrations were below 0.1 micrograms/ml. In contrast, absorption of SDZ was very rapid; values for tmax were 1.5-1.8 h. The pharmacokinetic parameters for SDZ were calculated according to a one-compartment open model; neither diet nor age had a significant effect on SDZ disposition following s.c. injection. Subcutaneous administration of 30 mg/kg Tribrissen, b.i.d., may be the best therapeutic regimen; even though measureable concentrations of TMP cannot be achieved in the serum following a single s.c. dose, TMP concentrations should accumulate and, because of its sustained release, provide almost continual potentiation of SDZ.

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.

Effect of duodenal cannulation on abomasal emptying and secretion in the preruminant calf

1. The effect of re-entrant cannulation of the duodenum on digesta flow from, and secretion into, the abomasum of the preruminant calf was studied. 2. Calves fitted with abomasal cannulas and, at the same time or later, with re-entrant duodenal cannulas were given, by abomasal infusion, test feeds containing glucose and minerals. Net volumes of secretory fluids entering the abomasum and amounts of digesta flowing to the duodenum were estimated from changes in concentrations of water soluble markers (phenol red and polyethylene glycol) in digesta samples collected from an abomasal cannula. 3. Amounts of abomasal contents, net volumes of secretory fluids and digesta flow to the duodenum for calves fitted with only an abomasal cannula did not differ significantly from those obtained for animals with abomasal and re-entrant duodenal cannulas. 4. Collecting digesta from a re-entrant cannula and returning it promptly to the animal did not affect net volumes of secretory fluids. Under these conditions with cannulas open to the atmosphere, rather than being connected together, the amounts of digesta entering the duodenum increased slightly but differences were not significant. 5. Weight gains of calves fitted with abomasal and duodenal cannulas were similar to those of intact animals. 6. It is concluded that in calves receiving liquid feeds duodenal re-entrant cannulation is a suitable preparation for investigating digestive processes of the abomasum.

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.

Absorption of magnesium by the young steer

1. Steers with rumen and simple duodenal cannulas were allowed to graze pasture or were given diets of dried grass or flaked maize with or without hay. For an experiment a solution or suspension of magnesium chloride, polyethylene glycol (molecular weight 4000) and either 144Ce (as cerous chloride) or chromic oxide was added to the rumen with a morning feed. Conditions in the rumen were sometimes modified by adding sodium chloride or hydrochloric acid. 2. Changes in magnesium:marker in samples of strained rumen contents with time interval after adding the dose were due partly to changes in Mg distribution between different phases. Results indicated, but not unequivocably, that negligible amounts of Mg were absorbed in the first few hours. 3. Relative recoveries of Mg and markers at the duodenum indicated that proportions of Mg intake absorbed (net) varied from approximately zero for pasture to 0.2--0.5 for flaked maize. Significant correlations between absorption efficiency and sodium:potassium in rumen contents (positive) and rumen pH (negative) were observed. 4. Steers with simple duodenal and re-entrant ileal cannulas were given a diet of flaked maize and hay supplemented with different amounts of magnesium oxide. Little net change in Mg relative to an unabsorbed marker was found between these sites even for a diet containing an Mg supplement of 8 g/kg dry matter.

Measurement of flow and sampling of digesta in the preruminant calf

1. Methods of measuring and sampling the flow of digesta passing through intestinal cannulas in preruminant calves were studied and compared. 2. The effect of collecting digesta from a duodenal cannula on abomasal emptying in a calf given whole milk was determined. When digesta were collected and returned to the duodenum manually in large amounts (about 200 g) the outflow of abomasal contents was intermittent. When digesta were returned to the animal either manually or automatically in amounts of less than about 50 g abomasal emptying was smooth. 3. An automatic apparatus for measuring and sampling the flow of digesta continuously was developed. The device allowed effluent to be returned smoothly to an ingoing cannula at the same rate that digesta left the outgoing cannula. After a feed of whole milk abomasal contents were observed to enter the duodenum in an orderly series of gushes. Each gush consisted of about 5--30 g of digesta. 4. The apparatus was rearranged to measure the effects of composition of duodenal digesta on abomasal emptying. Replacement of duodenal digesta with a suspension containing heated soyabean flour slowed the abomasal outflow of a feed containing casein. 5. Automatic apparatus was used to collect digesta arriving at the distal ileum. Withholding effluent from the large intestine did not affect the movement of digesta from the ileum.

Digestibilities of nitrogen compounds in rumen bacteria and in other components of digesta in the small intestine of the young steer

1. Mixed bacteria were obtained from the rumen contents of steers and were taken at different times after the animals had been given different feeds. The feeds contained [15N]urea and in some experiments Na2 35SO4 so that the bacteria were labelled with these isotopes. 2. Samples of labelled bacteria were subjected to a simulated abomasal digestion with pepsin and the digests were infused with a non-absorbed marker, polyethylene glycol, into the duodenums of test steers equipped with re-entrant ileal cannulas. Except for samples taken after a 24 h fast, which sometimes gave somewhat lower values, mean values for digestibilities of 15N and 35S in the small intestine were 0-79 and 0-85 respectively. 3. The corresponding value for the digestibility of 15N in similarly-treated wheat-leaf protein concentrate was 0-86. 4. Net digestibilities of total N in the small intestine of the test steers when they were given either a mainly protein-free diet of straw, tapioca and urea or a diet of flaked maize and hay were approximately 0-62. 5. From these and other values it was calculated that approximately 5-2 g intestinally-secreted endogenous N/d flowed through the ileum of a 100 kg steer.

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.

Rate of flow of digesta and electrical activity of the small intestine in dogs and sheep

1. Spiking activity of the small intestine in the conscious dog and sheep was recorded continuously from electrodes chronically implanted on the jejunum and summed at intervals of 20 sec. The activity was related to the transit time and flow rate of intestinal contents as estimated by phenol red and by dilution of continuous marker infusions respectively. Also in some sheep the flow of digesta was measured directly from a cannula in the proximal part of the jejunum, and also by use of an electromagnetic flow meter. 2. In the fasted dog and in sheep on a normal diet the intestinal activity was characterized by a migrating myo-electric complex comprising an irregular phase followed by a regular phase. These migrating myo-electric complexes occurred regularly after a period of inactivity at a frequency of 15-20/24 hr. In dogs after feeding, a continuous spiking activity appeared and persisted for periods of 7-8 hr. This was associated with much higher rates of flow and shorter transit times than were observed during fasting. In sheep, continuous spiking activity could be induced by intravenous injection of 5-hydroxytryptophan and this, similarly, was accompanied by a more rapid flow and a shorter transit time than recorded during the control period. 3. In both species the longest transit time occurred when a phenol red bolus was injected during the period of electrical inactivity. Relatively short transit times were observed when the bolus was administered just before the period of regular spiking activity. 4. When relaxation of the bowel was induced by intraperitoneal injection of hypertonic saline there was no spiking activity and the transit time for the infused solution was greatly lengthened, especially in the sheep. A noticeable flow of digestive contents persisted in the dog. 5. In the sheep the intestinal contents flowed intermittently during periods of 10-15 min and at the same frequency as the migrating myo-electric complex. Two thirds of this flow took place in the 4-6 min immediately preceding the periods of irregular spiking activity. 6. It is concluded that in the fasted dog and in the sheep the migrating myo-electric complex controls the pressure gradients on which the flow of intestinal contents depends. This is accomplished in the main by the prolonged phase of irregular spiking activity, and it is suggested that the regular spiking activity which follows it, though not in itself propulsive, serves as a barrier to prevent backflow of digesta into the quiescent part of the intestine. When continuous spiking activity is induced, by feeding in the dog and by injection of 5-hydroxytryptophan in the sheep, no part of the intestine is quiescent and the transit time is shortened by the incessant irregular spiking activity.

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.

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.

Mineral composition and rates of flow of effluent from the distal ileum of liquid-fed calves

1. Liquid-fed calves (aged 1(1/2)-4 months) examined more than five weeks after inserting a re-entrant fistula into the distal ileum, of normal sodium and potassium status and without abnormal gut infection, showed mean emergence rates from the ileum for sodium, potassium and water of 2.3 m-mole/hr, 0.38 m-mole/hr and 21 g/hr respectively after 16 hr fasting.2. Sodium and potassium emergence rates changed little when the residues from a milk or glucose-solution feed arrived at the distal ileum. When magnesium chloride was added to a glucose-solution feed an increase sometimes occurred but only in association with decreased small-intestine transit time.3. Widely differing sodium and potassium intakes had no appreciable direct effect on their emergence rates. Continued feeding of a diet deficient in either ion, however, altered the calf's metabolism and led to appropriate changes in the sodium/potassium ratio of ileal effluent. These changes were not simulated by injecting adrenal cortex hormones. The ratio also decreased when ileal effluent was allowed to discharge for several weeks without being returned to the colon. It was abnormally high in samples obtained less than five weeks after inserting cannulae.4. An increase in sodium and potassium emergence rates, which often occurred spontaneously at about 3 months of age, appeared to be due to infection and was usually prevented by giving aureomycin orally.5. Water emergence rate reflected changes in the emergence rates of osmotically effective constituents and isotonicity was maintained. In effluent after fasting, the cations involved were mainly sodium and potassium, and [Na] + [K] was approximately constant (mean 132 m-mole/l.). In effluent following feeds of milk or glucose, magnesium chloride solution, [Na] + [K] was depressed and [Na] + [K] + 1.5 [Mg] was approximately constant (mean 139 m-mole/l.). Magnesium behaved as it were mainly ionic. Calcium had no apparent osmotic effect and was probably insoluble.6. Bicarbonate was the major anion in ileal effluent after a milk feed with smaller amounts of chloride, phosphate and some other unknown anion(s).