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

Problems of calf rearing in connection with their mortality and optimal growth: A review

Protection of calves against enteric and respiratory disorders is dependent on the passive immunity that the calf has received, its innate resistance to infection, the burden of infection in the environment and the nutrition of the calf. Superimposed on these, are the effects of management and physical environment.

The plane of nutrition required for dairy heifers during rearing depends on the age at first calving, and for meat animals depends on the carcass weight and fat deposition required at a particular slaughter date in relation to time of birth.

Conjugated bile acids and intestinal flora during the preruminant stage in goat. Influence of a lamb milk replacer

A total of 45 preruminant goats were fed either goat milk or a milk substitute to compare the evolution of taurine and glycine conjugated bile acids and the evolution of the intestinal flora during the first month of life. Samples of hepatic bile were obtained from kids of 1, 7, 14, 21, and 28 days old and conjugated bile acids were measured by high performance liquid chromatography. Bacterial flora were determined in 14 and 28 day old animals. Ours results show that under our experimental conditions tauroconjugated bile acids clearly predominated over the conjugated with glycine. This pattern of preferential tauroconjugation persisted at all ages tested and in both groups studied. On the other hand, it seems that the quality of the protein and fat used in the elaboration of the milk replacer affects the intestinal flora and the postnatal evolution of conjugated bile acids.

Dietary factors affecting the maximum feed intake and the body composition of pre-ruminant kid goats of the Granadina breed

An experiment was carried out with kid goats of the Granadina breed to identify the dietary factors affecting voluntary feed intake of the kid goat and those that additively could determine its body composition. The animals used were from birth to 61 d of age, fed ad lib. on different milk replacers containing 200, 240 and 280 g crude protein/kg DM and 200, 240 and 280 g fat/kg DM, thus giving nine dietary treatments. The utilization of the milk replacers and the animals' body composition were determined by balance and slaughter trials. There were significant positive effects of protein concentration of the milk replacers on component digestibilities, energy metabolizability, feed intake, empty-body weights, empty-body composition and protein and fat retention. The concentration of fat in the milk replacers also had a significant positive effect on the digestible and metabolizable energy concentration of the diets and on fat retention. The relationships existing between feed intake and diet composition (concentration of digestible protein, metabolizable energy and digestible protein:metabolizable energy ratio) as well as between empty-body composition or protein and fat retention and diet composition, were examined. From these it was deduced that feed intake was significantly influenced by the digestible protein concentration of the diets. The higher the digestible protein concentration the higher the feed intake up to a maximum digestible protein concentration value. As the digestible protein concentration of the diets was the dietary factor which significantly influenced feed intake, this also significantly influences the body composition and the protein and fat retention. The protein concentration of the feed at which metabolizable energy intake in these animals would be greatest was estimated to be 347 g/kg DM.

Effect of dietary protein source on feed intake, growth, pancreatic enzyme activities and jejunal morphology in newly-weaned piglets

Seventy piglets with no access to creep feed were weaned at 28 d of age and fed on one of four diets based on either skimmed-milk powder (SMP), soya-bean-protein concentrate (SPC), soya-bean meal (SBM) or fish meal (FM). At 0, 3, 6 and 10 d after weaning, piglets were killed and the pancreas and digesta from stomach and small intestine were collected, freeze-dried and analysed for dry matter (DM), N, and trypsin (EC 3.4.21.4) and chymotrypsin (EC 3.4.21.1) activities. Small-intestinal tissue samples were taken to examine gut wall morphology. Results indicated that dietary protein source affected post-weaning feed intake, pancreatic weight, gastric pH and gastric protein breakdown, and pancreatic and jejunal trypsin and chymotrypsin activities. Post-weaning feed intake appeared to be an important factor in digestive development of newly-weaned piglets.

In vivo and in vitro gastric emptying of milk replacers containing soybean proteins

Gastric digestion of three milk replacers for which protein was provided either exclusively by milk powder or partially (50%) by heated soybean flour or soybean protein concentrate was studied in vivo and in vitro. In vivo gastric emptying of protein fractions of the diets was measured in six preruminant calves fitted with reentrant duodenal cannulas and used in a double 3 x 3 Latin square design. In vitro gastric emptying was studied after hydrochloric acid and rennet digestion in an artificial stomach. In vivo and in vitro flow rates of 12% TCA-insoluble N and total N were higher for the soybean diets than for the milk protein diet, indicating that the incorporation of soybean protein prevented casein from clotting. Because of this faster gastric emptying, proteolysis in the stomach was reduced. However, gastric emptying of NPN (12% TCA-soluble N) was significantly decreased only in vitro. No difference existed between the two milk replacers containing either soybean flour or soybean protein concentrate. In vivo and in vitro results were correlated, suggesting that the in vitro method could be used to predict gastric digestion of protein fractions in vivo.

[Influence of emulsifiers and fat mixtures on the digestibility and sedimentation of fatty acids in calves]

In a digestibility experiment with 4 X 4 calves the animals received 100 g mixture for calves, 50 g dried green fodder and either 656 g dried whole milk and 164 g dried skim milk (VM) or 656 g dried whole milk and 164 g added fat. The added fat consisted of a mixture of tallow and lard in a 1:1 ratio plus 10% emulgator ES 20 (FE) or 8% ES 20 and 2% soybean lecithin (FL) or 25% lard, 25% tallow, 40% rape/sunflower oil with 10% ES 20 (FO). The apparent digestibility of the fat amounted to 91% in group VM and in groups FE/FL/FO to 66/70/67% resp. The composition of fatty acids and the use of an unsuitable charge of dried skim milk are considered to be the causes of the low apparent digestibility. The apparent digestibility of the fatty acids decreased with their growing chain length. The higher digestibility of the unsaturated fatty acids is largely caused by changes due to bacterial activity in these fatty acids in the intestines and by the influence of metabolically changed faecal fat. The combination of the synthetic emulgator with lecithin did not improve fat digestion but diminished the total fat content in the blood.

Use of a nylon-bag technique for pig feed digestibility studies

1. The use of a nylon-bag technique for pig feed digestibility determination was studied. Bags, measuring 25 x 40 mm and containing feed samples, were introduced into the pig gastrointestinal tract through a duodenal cannula, and recovered in the faeces between 23 and 69 h later. The disappearance of organic matter and crude protein (nitrogen x 6.25) from the bags was compared with in vivo apparent digestibility, determined by conventional faecal-collection methods, and neutral-detergent-fibre content for eleven feeds. The residues left in the bags after passage through the intestine from whole-crop-pea (Pisum sativum) and barley-grain samples were analysed for starch, non-starch polysaccharide residues, Klason lignin, crude protein and ash. 2. Dry matter disappearance of barley or whole-crop peas was not influenced by increasing bag pore size from 10 to 36 microns or sample weight from 250 to 1000 mg. Pepsin (EC 3.4.2.1) pretreatment had no effect on the degradation in the bags of the feeds investigated. 3. Organic matter and crude protein disappearance from the bags exceeded in vivo apparent digestibility by up to 0.10 and 0.42 units respectively. In vivo apparent organic matter digestibility could be predicted (P less than 0.001) by the organic matter disappearance from the bags and the neutral-detergent-fibre content of the feed, while in vivo apparent crude protein digestibility was highly correlated (P less than 0.001) to all these indices but poorly to crude protein disappearance from the bags. 4. Klason lignin was the least degraded component measured in the whole-crop-pea and barley residues from the bags, while starch was completely digested.(ABSTRACT TRUNCATED AT 250 WORDS)

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 digestion of protein in young pigs and the utilization of dietary methionine

Forty pigs between 23 and 51 d of age were given ad lib. diets containing wheat and one of five protein concentrates: meat meal A, meat meal B, soya-bean meal, milk and lupins (Lupinus augustifolius). Twenty of these pigs were given indigestible markers from 51 to 56 d of age and were killed at 56 d of age. The diets containing meat meals A and B, soya-bean meal and milk contained 2.3 g total methionine/kg and the diet containing lupins contained 2.1 g/kg. A further forty pigs of the same age were given the same diets supplemented with 1 g synthetic methionine/kg. The weight gains and feed conversion ratios of the pigs given the diets containing 2.1-2.3 g methionine and 3.1-3.3 g methionine/kg were not significantly different. The weight gains of the pigs given lupins (2.1 g methionine/kg) were less than those of the pigs given the diets containing 2.3 g methionine/kg. The apparent digestibility of dry matter (DM) and nitrogen was less for the diets containing the meat meals (0.75 and 0.78 respectively) than for those containing the other protein concentrates (0.80 and 0.84). The retention times in the large intestine of the diets containing soya-bean meal and lupins were 965 and 1083 min which were greater than those of the diets containing the other protein concentrates, mean 732 min. The major site of N digestion and absorption for the diet containing milk was the area of the small intestine 25-50% of total length from the pylorus, while for the other protein concentrates the major site was 50-75% of its total length from the pylorus. The digestion and absorption of N in the large intestine was less (3.4%) for the diet containing milk than for those containing the other protein concentrates (7.5-11.3%). The apparent digestibility of the methionine to the ileum for the five diets ranged from 0.74 to 0.86 while the calculated retention of the apparently-absorbed methionine was 1.00. It was suggested that methionine digestibility could be used as an indicator of availability. The calculated retention of apparently absorbed N in the carcass was 0.71 for the pigs given the diet containing milk and 0.51-0.58 for the pigs given the other diets.

Insulin and gastric inhibitory polypeptide secretion in young milk-fed and adult goats

Plasma concentrations of glucose, immunoreactive insulin (IRI), and immunoreactive gastric inhibitory polypeptide (IR-GIP) were studied in six adult and five young milk-fed goats after intravenous or intraduodenal infusions of glucose. Glucose concentrations after intraduodenal infusions were elevated from 3.5 to 4.7 mmol/liter on the average in adult and from 4 to 7 mmol/liter in young goats. Intravenous infusions were given at rates adjusted to mimic very closely the plasma glucose curves after intraduodenal infusions. Plasma IRI increased from 250 to 600 pmol/liter in adult and from 180 to 500-600 pmol/liter in young goats, but no significant differences were observed between intravenous and intraduodenal infusions. Duodenal infusions of glucose did not stimulate the release of IR-GIP in adult or young goats. It is concluded that the goat is lacking the incretin system for rapid disposal of oral glucose loads and that IR-GIP does not participate in regulation of glucose-stimulated insulin release in this species.

Digestion in the pig between 7 and 35 d of age. 6. The digestion of hydrolyzed milk and soya-bean proteins

1. Four pelleted diets were prepared containing milk or isolated soya-bean protein (ISP) as the major protein source. The milk and ISP were given either as intact proteins or partially (0.650 hydrolyzed with papain before feeding. 2. The diets were given ad lib. to thirty-two pigs from 7-28 d of age. The pigs were slaughtered at 28 d of age. 3. Weight gains, food conversion ratios and nitrogen balances of pigs given diets containing milk protein were better than those of diets containing ISP (231 g/d, 0.80 and 11.5 g/d compared to 209 g/d, 0.88 and 9.00 g/d respectively). 4. Partial hydrolysis of proteins before feeding did not affect the performance of the pigs. 5. Apparent digestibilities of N before the ileum and in the whole tract were 0.78 and 0.94 for the pigs given the ISP diets and 0.86 and 0.97 for the pigs given the milk-protein diets. 6. Retention time of ISP diets in the whole digestive tract was 1475 min and that of the milk-protein diets was 1089 min. 7. pH of digesta in the stomach was 5.0-5.3 for all diets and increased to 6.9-7.1 in the ileum. 8. There were no differences in flows of total N and protein N to the ileum and lower digestive tract between the pigs given the intact-and hydrolyzed-protein diets. 9. Apparent absorptions of N in the stomach, duodenum and jejenum were greater in the pigs given diets containing hydrolyzed proteins than in those given diets containing the intact proteins. 10. Flows of total N and protein N to the ileum tract were greater when the pigs were given the ISP diets than when they were given the milk-protein diets. 11. Hydrolysis of proteins before feeding resulted in a reduced trypsin and chymotrypsin activity in the duodenum and pancreas. 12. Retention of dietary N in the carcass was greater in pigs given the milk-protein diets (0.79) than in those given the ISP diets (0.68).

Digestion in the pig between 7 and 3 d of age. 3. The digestion of nitrogen in pigs given milk and soya-bean proteins

1. In two separate experiments, forty-four pigs weaned at 4--5 d of age were fed on diets containing milk or soya-bean protein until slaughtered at 14, 28 or 35 d of age. 2. Daily amounts of nitrogen flowing through the stomach and proximal small intestine of pigs were similar with both sources of protein fed. 3. Endogenous N flows in the duodenum, jejunum and ileum of pigs given an N-free diet were 22 . 9, 7 . 4 and 4 . 6 g N/kg dry matter (DM) intake. Endogenous N in faeces was 0 . 970 g N/kg DM intake. 4. The apparent and true digestibility of N to the ileum of 28-d-old pigs was 0 . 86 and 0 . 92 for the pigs given the milk-protein diets, 0 . 80 and 0 . 86 for the pigs given the isolated soya-bean protein (ISP; Promine D) diets and 0 . 51 and 0 . 62 for pigs given the soya-bean meal (SBM)-protein diet. These values over the entire gastro-intestinal tract were 0 . 98 and 1 . 00 for milk, 0 . 92 and 0 . 95 for ISP and 0 . 82 and 0 . 85 for SBM. 5. The apparent and true digestibility of N to the ileum of 14-d-old pigs given a liquid milk diet was 0 . 92 and 0 . 94, while the values for the pigs given a pelleted milk diet were 0 . 86 and 0 . 87. At 35 d of age there were no differences in the apparent digestibility of the N in the liquid an pelleted milk diets. 6. The apparent digestibility of N to the ileum and over the entire gastro-intestinal tract of pigs given ISP (Supro 610) increased with increasing age of pigs from 0 . 83 at 14 d of age to 0 . 88 at 35 d of age. 7. Of the N in the stomach 14--32% could not be precipitated by trichloroacetic acid (TCA; 30 milligram). 8. In the jejunal and ileal contents an average of 46 and 24% of the N was precipitated by TCA in pigs given soya-bean proteins and milk proteins respectively.

Concurrent studies of the flow of digesta in the duodenum and of exocrine pancreatic secretion of calves. 7. Influence of milk substitutes on abomasal lipolysis and biliary secretion

1. The abomasal hydrolysis of lipids and the flow of endogenous (biliary) lipids was studied in two Friesian calves given four milk-substitute diets, by sampling the duodenal digesta. The diets were: reconstituted, mildly preheated, spray-dried skim-milk powder with (SKF) or without (SK) margarine fat or with 500 g/kg skim-milk powder in diet SKF replaced by soy-beran flour (ASKF) or fish-protein concentrate (BSKF) together with dried whey. The diets were given ad lib. twice daily from 13 to 37 d of age, each diet being given for six consecutive days. Collections of duodenal digesta from the re-entrant cannula situated caudal to the bile duct were made for 12 h after feeding the 6th and 12th meals for each diet. Samples from one collection only were subjected to detailed analysis of the lipid classes. 2. The inclusion of non-milk protein (ASKF and BSKF) not only increased the rate of passage of lipid through the abomasum but also the proportion of the lipid present as triglyceride particularly, in the first 2 h after feeding. 3. In a 12 h period, 2.3-6.3 g 'polar' lipids (mainly biliary phospholipids) were estimated to have been secreted. The rate of flow was high during the first hour after feeding and constant thereafter. The quantity of 'polar' lipid was not related to the type of milk fed or the duodenal flow of lipid. 4. When diet SK was fed, the small amounts of lipid present were extensively hydrolysed so that free fatty acids represented 700 g/kg lipid of dietary origin passing through the duodenum. When margarine fat was included in the diets (SKF, ASKF and BSKF), the free fatty acids represented only 210 g/kg lipid of dietary origin. 5. The quantities of lipid and nitrogen passing through the duodenum were poorly related to the quantities ingested at the beginning of the 12 h experimental period but were closely related to each other.

Symposium: disease prevention in calves. Factors affecting susceptibility of calves to disease

Enteric and respiratory disorders are the main hazards to successful calf rearing. The many interrelated factors in the etiology of these disorders are reviewed, and an attempt has been to classify the factors into those of a microbiological, immunological, nutritional, genetic, physical, or psychological nature. No one would dispute that enteric and respiratory disorders are the two main hazards to calf health, but many would argue about the relative importance of specific pathogens and other predisposing factors in the etiology of these disorders.

Abomasum emptying in dairy calves fed milk replacers with varying fat and sources of protein

Young Holstein male calves fitted with reentrant duodenal fistulae were in two 3 x 3 Latin square experiments. In the first experiment the calves were fed milk replacers containing either 5%, 15%, or 25% lard. Total nitrogen, protein nitrogen, and fat left the abomasum more slowly for the 5% fat milk replacer than for the other two milk replacers. In the second experiment, the calves were fed milk replacers containing either whey proteins, whey, and fish proteins (50:50), or whey and soybean proteins (50:50). Dry matter, total nitrogen, protein nitrogen, and nonprotein nitrogen left the abomasum more slowly for the milk replacer containing whey and soybean proteins than for the other two milk replacers. In both experiments, milk replacers did not differ in rates of passage of fresh matter, reducing substances, ash, gastric secretion of hydrochloric acid, gastric proteolysis, and diarrhea. In Experiment 1, milk replacers did not differ in rates of passage of dry matter and nonprotein nitrogen. In Experiment 2, milk replacers did not differ in rate of passage of fat. Circadian rhythm had no influence.

Concurrent studies of the flow of digesta in the duodenum and of exocrine pancreatic secretion in calves. 6. The effect of feeding warm or cold milk by bucket or teat

1. The effects of bucket- v. teat-feeding and warm- v. cold-milk feeding on the flow of duodenal digesta and the concurrent pancreatic secretion were studied in two experiments in preruminant Ayrshire calves (28–43 d of age), fitted with duodenal re-entrant and pancreatic sac cannulas.

2. As measured by the time interval taken for total recovery of the polyethylene glycol fed in the milk, the whey fluids had a more rapid passage through the abomasum when the calves were given warm milk by teat rather than by bucket (Expts 1 and 2). The duodenal digesta contained less sodium ions and more ‘Cl-Na+’ when the calves were fed by teat even though the volumes of milk drunk and duodenal flow were similar. It was concluded that more abomasal acid was secreted when calves were fed by teat.

3. When the calves were fed by teat rather than by bucket, the protein-nitrogen : N (PN : N) in the duodenal digesta was lower, especially during the first 6 h after feeding and there was a tendency for more pancreatic proteases to be secreted.

4. In Expt 1, when the calves were given warm milk the total flow of N and lipid in the duodenal digesta was 22 and 19% greater than that ingested. This was considered to be due to the coagulum from the penultimate meal plus the experimental meal passing more readily through the duodenum when sampling and to endogenous secretion of N and lipid.

5. When four Ayrshire calves were bucket-fed cold, rather than warm milk there was a reduced secretion of abomasal and pancreatic fluids and abomasal acid. There were no differences in the time interval required for the whey fluids to leave the abomasum or the PN : N value.

6. There was a positive correlation between the total duodenal flow of non-whey fluids and the pancreatic secretion regardless of the method of feeding.

7. The completeness of digestion and susceptibility of calves to diarrhoea when fed by teat and bucket is discussed.

Concurrent studies of the flow of digesta in the duodenum and of exocrine pancreatic secretion in calves. 5. The effect of giving milk once and twice daily, and of weaning

1. The effects of giving milk once or twice daily (Expt 1) and of weaning (Expt 2) on the flow rate of digesta through the duodenum and on pancreatic secretion were studied in four and two Ayrshire calves respectively. The calves were prepared with duodenal re-entrant and pancreatic sac cannulas. 2. In Expt 1, when whole milk was offered ad lib. once daily, the calves ingested 141 g/kg live weight (46 g dry matter (DM)/kg live weight 0.75) at a single meal. The subsequent pattern of flow and total recovery of polyethylene glycol from the duodenum suggested that none of the ingested milk passed into the rumeno-reticulum. As the total daily quantity of milk ingested when the calves were fed once and twice daily was similar, it was concluded that abomasal distension is unlikely to be the sole factor limiting milk intake in the preruminant calf. 3. With twice-daily feeding, there were no differences in the pattern or total flow of fluid, electrolytes, nitrogen or fat through the duodenum of the calves following the 09.00 and 21.00 hours meals. The pattern of flow of duodenal and pancreatic fluids and the concentration of electrolytes, N and fat were markedly different when the calves were fed once or twice daily. The patterns of flow of fluid and the concentration of electrolytes in the duodenal digesta reflected the frequency of feeding and the size of the meal and the consequent balance between feed and endogenous components of the digesta. The quantity of the apparent endogenous secretion and pancreatic secretion was markedly less when the calves were fed once daily. 4. In Expt 2, the two Ayshire calves were given whole milk twice daily (diet MM), whole milk once daily with concentrates (diet MC), concentrates alone (diet CC) or dried grass alone (diet DG). The calves consumed 46, 49, 45 and 51 g DM/kg live weight 0.75 when given diets MM, MC, CC and DG respectively. 5. The twice-daily fluctuations in the flow and concentration of fluid, electrolytes, N and fat in the duodenal digesta and the pancreatic fluid observed when diet MM was given were replaced by relatively constant flow rates and composition when diet CC or DG was given. 6. Over the 24 h experimental period 97, 70, 50 and 58% of the DM and 112, 98, 99 and 84% of the N in the feed passed through the duodenum of calves when given diets MM, MC, CC and DG respectively. 7. When dry food was given, the rate of pancreatic fluid secretion was markedly lower (11.3 and 13.5 ml/kg live weight for diets CC and DG respectively) than when diet MM (19.7 ml/kg live weight) was given.

Concurrent studies of the flow of digesta in the duodenum and of exocrine pancreatic secretion of calves. 4. The effect of age

1. The effect of age on the flow of duodenal digesta and of pancreatic secretion was studied in preruminant calves fitted with duodenal re-entrant and pancreatic sac cannulas. In Expt 1 a comparison was made at 7, 24 and 63 d of age of Ayrshire calves given whole milk, and in Expt 2 Friesian calves given milk-substitute diets were studied during the period 16–37 d of age.

2. For the Ayrshire calves, ad lib. whole-milk intake increased with age, but whole-milk intake on a per kg metabolic body-weight (W0.75) basis did not alter. As the intake increased with age, the whey fluids were passed out of the abomasum more rapidly.

3. As judged by the mean duodenal pH values and the values for ‘chloride ion minus sodium ion’ concentration in the digesta, and for apparent secretions (total quantity recovered at duodenal cannula during 12 h after feeding minus intake) the duodenal digesta became more acid as the Ayrshire calves became older. There was no change with age in the extent of degradation of the milk proteins as indicated by the protein-nitrogen: total N values for duodenal digesta.

4. The volume of pancreatic fluids secreted by the Ayrshire calves increased markedly with age, but when expressed on a per kg W0.75 the volume did not increase after 24 d of age. In absolute terms and also in relation to whole-milk intake or W0.75 there was a large increase in secretion of total protease, a very large increase in α-amylase (EC 3.2.1.1) but no change in trypsin (EC 3.4.4.4) activities with age.

5. In the Friesian calves secretion of pancreatic fluid and activities of α-chymotrypsin (EC 3.4.4.5), α-amylase, lipase (EC 3.1.1.3) and ribonuclease (EC 2.7.7.16, 2.7.7.17) but not trypsin or total protease increased with age.

6. The extent of the increase in secretion of pancreatic enzymes during the first hour after the Friesian calves were fed milk-substitute diets differed between enzymes.

7. The changes in the quantities of pancreatic enzymes secreted are discussed in relation to the changes in the digestibility of milk-substitute diets.

Milk-substitute diet composition and abomasal secretion in the calf

1. The effect of different protein sources in milk-substitute diets on abomasal acidity and proteolytic activity was studied in Friesian calves, aged 20-58 d (Expt 1). The diets contained 'mildly' preheated, spray-dried skim-milk powder (MHM), severely preheated, spray-dried skim-milk powder (SHM), fish-protein concentrate (FPC) or solvent-extracted soya-bean flour (SF) as the main protein source. 2. Gastric juice was collected from abomasal pouches before feeding and at 15 min intervals for 8 h after the morning feed. Samples of digesta were obtained from the abomasum at 1 h intervals during the same period. 3. Digesta pH was lower and titratable acidity higher 0-3 after giving the diet containing MHM than when any of the other three diets was given. 3. Acid secretion from the pouches for the different diets was in the order: FPC greater than MHM greater than SHM greater than or equal to SF. 5. Protease secretion from the pouches, assayed at pH 2-1, was in the order: MHM greater than SHM = FPC greater than SF. 6. The effect of dry matter (DM) intake and concentration on abomasal acidity was also studied in calves given diets which contained MHM (Expt 2). This diet was reconstituted at either 100 or 149 g DM/kg liquid diet and fed at either 32-5 or 49-0 g DM/kg live weight 0-75 per d. Samples of abomasal digesta were collected as in Expt 1. 7. A high intake of DM at a low DM concentration resulted in low acidity of the digesta in the first 3 h after feeding, which suggested a dilution effect. Comparison of two diets of different DM concentration, which were fed in the same volume of liquid, indicated that the greater the DM intake, the greater was the amount of acid secreted. 8. It is concluded that the protein sources varied in their ability to stimulate abomasal acid and protease secretion and it is suggested that this may relate to calf performance.

Concurrent studies of the flow of digesta in the duodenum and of exocrine pancreatic secretion of calves. 3. Further studies on the addition of fat to skim milk and the use of non-milk proteins in milk-substitute diets

1. The flow of digesta through the duodenum and the concurrent secretion of the pancreas were studied in four Friesian calves given four milk-substitute diets. The diets were: reconstituted, "mildly" pre-heated, spray-dried skim-milk powder with (SKF) or without (SK) margarine fat or with 5o percent of the skim-milk powder in diet SKF replaced by soya-bean flour (ASKF) or fish-protein concentrate (BSKF), together with dried whey. The diets were given ad lib. twice daily from 13 to 37 d of age, each diet being given for 6 consecutive days. Collections of duodenal digesta and pancreatic secretions, from cannulas, were made for 12 h after feeding the 6th and 12th meals ("experimental" meals) for each diet. 2. The diets fed as "experimental" meals contained polyethylene glycol (PEG) as a fluid (whey) marker and goat's milk containing (3H)lysine as a marker for total protein; beta-carotene was added as a lipid marker to the three diets containing margarine fat. 3. Over the 12 h postprandial period, the patterns of duodenal digesta flow and secretion of pancreatic fluid did not differ markedly between the four diets. The abomasal outflow of both nitrogen and lipid in a 12 h postprandial period was related to their intakes from the "penultimate" (5th and 11th) meals for diets SKF and SK BUT TO THEIR INTAKES AT THE "EXPERIMENTAL MEALS" FOR DIETS ASKF and BSKF. Secretion of pancreatic enzyme activity was highest during the 1st hour after feeding but the main outflow from the abomasum of total N and lipid occurred 5-10 h after feeding. 4. The time required for all the whey marker (PEG) to pass through the duodenum was similar for diets SKF and SK, but only 53 and 42 percent respectively of the ingested protein marker passed through the duodenum in the 12 h after feeding. More acid appeared to be secreted by the abomasum when diet SK was given; also less undigested protein passed out of the abomasum after giving this diet. It is concluded that the physical absence of fat globules in the abomasal clot increases the degree of proteolysis. 5. The secretions of pancreatic fluid and pancreatic enzyme activity were all markedly lower for diet SK than for diet SKF. 6. With diets containing non-milk proteins (ASKF and BSKF), abomasal proteolysis was less efficient and the ingested protein passed out of the abomasum more rapidly than for diet SKF. There was no difference in the rate of abomasal outflow of the whey fluids between diets SKF, ASKF and BSKF. 7. In comparison with diet SKF, diets ASKF and BSKF tended to induce less pancreatic enzyme secretion over a 12 h postprandial period, with the exception of lipase. 8. There appeared to be no direct relationship between the quantities of any of the pancreatic enzymes secreted during a postprandial period and either the concurrent flow of duodenal digesta or the total quantities of dietary constituents passing through the duodenum.