1. Four sheep, each fitted with a rumen fistula and a re-entrant cannula at the proximal duodenum were fed a semi-purified diet containing urea as the only nitrogen source. The quantities of total protozoal amino acid-N (TPAN) present in the rumen and entering the duodenum were determined when the mean rumen dilution rate (D) was low (0.034/h) and when D was increased to 0.078/h by the intraruminal infusion of artificial saliva.

2. Increasing the dilution rate had no significant effect upon the proportions of TPAN present in the total microbial amino acid-N (TMAN) of the rumen fluid and duodenal digesta. With both dilution rates the mean proportion of TPAN in the duodenal TMAN (0.24) was markedly less than the equivalent proportion (0.45) found in the rumen fluid.

3. The daily flow of TPAN, as measured at the duodenal cannula at both dilution rates was equivalent to only 41 % of the flow of TPAN as predicted from measurements of rumen outflow, indicating that a substantial proportion of rumen protozoal protein was retained within the rumen.

1. Pigs were weaned at 2 d of age and fed on a milk substitute at hourly intervals. They were slaughtered at 28 d of age.

2. The diets contained 730 g dried skim-milk and 270 g fat/kg dry matter (DM). Three diets were compared in which the fat was supplied as soya-bean oil (SO) (diet A), equal amounts of SO and medium-chain triglyceride (MCT) (diet H), or 246 g MCT and 24 g SO (diet I)/kg DM. In the latter diet, SO ensured that the diet had an adequate content of essential fatty acids.

3. Growth rate (2–28 d of age) was reduced (P < 0.05) by the high-MCT diet (diet I) compared with the medium-MCT diet (diet H), but in comparison with diet A, the differences were not significant (P > 0.05). The feed: gain ratio (g DM consumed/g live-weight gain) was not affected by the type of dietary lipid.

4. Diet I increased the proportion of crude protein (nitrogen × 6.25) (g/kg wet weight) in the carcass but did not increase N retention (g/d per kg live weight). The proportion of fat in the carcass was reduced, particularly by diet I (P < 0.001), and was inversely related to an increase mainly in the water content, and to a lesser extent, in the crude protein content of the carcass. The liver weight (g/kg live wt) was greatly increased by MCT (P < 0.01 or P < 0.001).

5. Approximately 20, 44 and 80% of the fatty acids in the carcass of pigs on the SO, diet H and diet I respectively could not have been derived from direct deposition of the dietary fatty acids, but rather by de novo synthesis from carbohydrate or elongation of shorter-chain fatty acids.

MCT increased the concentrations in the blood, taken 1 h after feeding, of total lipid, phospholipid, cholesterol and cholesterol ester, indicating incomplete oxidation of the caprylic and caprylic and capric acids in MCT by the liver, and their incorporation, after chain elongation, into plasma lipids.

1 A series of experiments were conducted to investigate the effects of dietary retinol status on chickens ingesting aflatoxin B1. The effects of dietary supplementation with biotin and α-tocopherol were also examined.

2. Aflatoxin B1 levels greater than I mg/kg diet had a detrimental effect on ‘liveability’, body-weight gain, food intake and food conversion efficiency. When fed for more than 2 weeks aflatoxin increased relative liver weight and liver lipid concentration. These effects were less pronounced with avitaminotic A chickens.

3. A synergistic effect on hydropericardium development was observed between aflatoxin B, and retinol. This effect was not observed when the dietary level of α-tocopherol was increased tenfold.

4. The specific activities of certain hepatic lipogenic and amino acid-metabolizing enzymes were influenced by aflatoxin ingestion. A reduction in lipogenic enzyme activity was observed before a reduction in the activities of amino acid-metabolizing enzymes.

5. Liver fatty acid composition was significantly influenced by aflatoxin B1. The extent of these changes was reduced by the inclusion of additional dietary biotin.

1. The requirement of the artificially-reared pig for crude protein (nitrogen × 6.38; CP) was estimated between 2 and 28 d of age. The pigs were given one of five diets, each containing 270 g soya-bean oil/kg and either dried skim-milk and dried whey in different proportions to supply 150, 180, 210 or 240 g CP/kg, or dried skim-milk alone which supplied 270 g CP/kg. The energy content of the diets was approximately 22 MJ digestible energy/kg.

2. The diets were obtained as spray-dried powders, reconstituted in water, and fed as a liquid containing 200 g DM/l. The pigs were fed at hourly intervals to a scale based on live weight.

3. N retention (g/d per kg live weight) and the proportion of CP in the carcass indicated a CP requirement of 240 g/kg for pigs from 2–28 d of age.There was no significant difference (P > 005)in performance between levels of dietary CP of 2.10, 240 or 270 g/kg. Although there was no increase in the proportion of CP in the carcass above a dietary CP level of 240 g/kg, a linear reduction in the proportion of lipid occurred as dietary CP level increased from 150 to 270 g/kg. Mortality, which was associated with scouring, was increased when the diet contained less than 210 g CP/kg.

4. There was a linear response in N retention to the level of CP in the diet at 7 d of age, whereas at 19 d of age, N retention reached a maximum with 240 g CP/kg diet, suggesting that the CP requirement may be greater during the first week of life.

5. Excretion of endogenous N in the urine was found to be 250 mg N/d per kg live-weight0.75 in pigs between 7 and 19 d of age (20–6.4 kg live weight).

1. Young pigs were fed on three diets consecutively, each diet being given for 1 week. The diets were given in random order as (g pig feed/kg body-weight): (a) 20, (b) 60, (c) 20 plus a supplement with the energy equivalent of 40 g pig feed/kg. The supplements included desiccated coconut, fish meal and glucose.

2. At the end of each week resting metabolic rate, beginning 12–14 h after feeding, was measured overnight using an open-circuit respiration chamber at thermoneutrality.

3. The oxygen consumption of pigs on the 60 g/kg diet was always higher than on the 20 g/kg diet. The addition of desiccated coconut, or fish meal also increased metabolic rate; whereas with added glucose, O2 consumption tended to be even lower than on 20 g/kg alone.

4. The administration of the β-blocker propranolol to pigs on ad lib. food intake reduced the rate of overnight resting O2 consumption, measured from 10 until 20 h after feeding, by 12%, but it had no effect on O2 consumption when the intake was 20 g feed/kg. Exposure to mild cold (15°) caused an increase in O2 consumption and this was reduced by 14% after injection of propranolol.

1. Half (diet M) or total replacement (diet N) of dried skim-milk by fish-protein concentrate and dried whey was compared with a diet containing dried skim-milk (710 g/kg) as the only source of protein (diet A). All three diets were prepared as spray-dried powders, and contained 20 g starch and 270 g soya-bean oil/kg. The diets were calculated to be isonitrogenous, but upon analysis had crude protein (nitrogen × 6.25) contents (g/kg) of 230, 270 and 291 in diets A, M and N respectively.

2. The diets were reconstituted as liquids containing 200 g dry matter (DM)/l and given to pigs weaned at 2 d of age during a 26 d experiment. The diets were fed at hourly intervals to a scale based on live weight. Protein digestion was studied in pigs, 6 d of age, and killed 1 h after a feed.

3. Live-weight gain was slightly improved when half the dried skim-milk was replaced, but the feed: gain ratio (g DM consumed/g live weight gain) was unaltered. Total replacement of dried skim-milk, markedly reduced performance and increased the incidence of scouring and mortality.

4. Increasing the proportion of fish protein reduced the apparant digestibility (AD) and the retention of N (g/d per kg live weight). N retention, but not AD, decreased with age.

5. Total replacement of dried skim-milk decreased the amount of digesta in the stomach, its pH value, and the proportion of DM and total N in the digesta, but non-protein N as a proportion of total N was increased.

6. The total pepsin activity in the stomach digesta was decreased by the substitution with fish protein, but there was no change in the activity of the stomach tissue. Trypsin and chymotrypsin activities in the pancreas were not affected by the source of dietary protein, but in the digesta of the small intestine the activity of these two enzymes was markedly reduced when the diet contained fish protein.

7. Total replacement of dried skim-milk with fish-protein concentrate and dried whey may increase the rate of flow of digesta through the small intestine, which together with the reductions in the apparent digestibility of N and amounts of trypsin and chymotrypsin in the digesta could reduce the efficiency of protein digestion and adversely affect performance.

1. Two experiments were conducted with lambs sustained entirely by intragastric infusion of volatile fatty acids (VFA), protein, minerals and vitamins.

2. In the first experiment to determine the effects of VFA on nitrogen retention four mixtures of VFA (B, C, D and E) were used containing acetic, propionic and butyric acid in the following molar proportions respectively: 45,45 and 10; 55,35 and 10; 65,25 and 10; 75, 15 and 10.The level of infusion was 836 kJ/live weight0.75 per d and the design was a 4 × 4 Latin square with 14 d periods. There were no significant differences in the N balance between the different mixtures of VFA though mixture B tended to give the highest N retention.

3. Thirty-two lambs were used in the second experiment for measurements of heat production in closed- circuit respiration chambers. Six mixtures of VFA were used. These included mixtures B-E from Expt I and in addition two mixtures (A and F) containing acetic, propionic and butyric acid in the following molar proportions respectively: 35, 55 and 10; 85, 5 and 10. The heat production was measured both at 450 and 900 kJ/W0.75 per d, except for mixture F, where it was not possible to achieve a rate of infusion in excess of 675 kJ/W0.75 per d.

4. The energy required for maintenance was determined to be 0.45±0.02 MJ/kg live weight0.75 per d regardless of the mixture used.

5. The efficiency of utilization for fattening (kf) values for the six mixtures were 0.78, 0.64, 057, 0.61, 0.61 and 0.59 for mixtures A, B, C, D, E and F respectively. Only mixture A was significantly better utilized than the other mixtures. This mixture also gave the most efficient N utilization.

6. It is concluded from this evidence that differences in k, for diets normally given to ruminants cannot be attributed to differences in utilization of volatile fatty acids.

A technique is described for feeding young sheep for long periods entirely by the infusion of volatile fatty acids into the rumen and protein and other essential nutrients into the abomasum. When the energy infused was twice the estimated requirement for maintenance, growth rate and nitrogen retention were essentially the same as in normally-fed sheep.

1. Food intake and rates of protein, lipid and energy deposition were measured for lean and obese (fatty) Zucker rats offered to appetite from 34 d of age to slaughter at 66 d of age, one of sixteen semi-synthetic diets. Measurements were also made of the digestibility of dietary protein and the metabolizability of dietary energy. Total carcasses were analysed for protein and lipid, and body energy was calculated thereby. Changes in body constituents were calculated by the comparative-slaughter technique.

2. In Expt 1, four rats of each phenotype and sex were offered one of four diets, each of which contained either 150 or 300 g casein (150 C and 300 C respectively)/kg and either 150 or 300 g cellulose (150 CELL and 300 CELL respectively)/kg (diets 150 C/150 CELL, 150 C/300 CELL, 300 C/150 CELL and 300 C/300 CELL. As expected, males ate more and had higher rates of protein deposition than female animals of the same phenotype on all diets. These sex differences were greater for the lean phenotype. The results for animals in this experiment are presented with, and discussed in relation to, those obtained previously for animals of both sexes fed on cellulose-free diets having these two levels of casein.

3. In Expt 2, four female animals of each phenotype were fed one of twelve semi-synthetic diets, each of which contained casein, gluten or zein at one of the following levels (g crude protein (nitrogen × 6.25)/kg diet): 93, 132, 267 or 627. On all diets containing zein both fatty and lean rats had similar, low food intakes and failed to grow. Fatty rats fed on diets containing casein or gluten had higher rates of food intake, weight gain, lipid and energy deposition than leanrats, but similar rates of protein deposition. Rats fed on diets having the two lower levels of casein ate more and grew better than animals of the same phenotype fed on the two corresponding diets containing gluten but at higher protein levels differences in food intake and growth attributable to differences in protein quality disappeared and furthermore, the rate of protein deposition became similar and maximal for both phenotypes.

4. The results from both experiments are discussed in relation to previous work on appetite control in the Zucker rat. It appears that fatty and lean rats eat during growth to attain the maximal rate of protein deposition of which they are capable. The rate of lipid deposition would appear to be of no importance in the food intake regulation of animals depositing protein maximally.

5. Rats given diets that fail to support maximal rates of protein deposition appear to regulate their intake of digestible energy rather than that of digestible protein. They do not overeat protein-deficient diets in order to acquire sufficient protein for maximal growth although the factors that induce satiety in these animals are unknown.

1. To investigate the effects of sulphur intake on molybdenum metabolism in sheep, ewes were given intakes of 0.3 or 3.5 mg Mo and 0.98, 1.33, 1.73 or 3.23 g S/d in a 2 × 4 factorial experiment with two replicates lasting 35 d. 99Mo with 0.1 mg carrier Mo was infused intravenously for the last 14 d and, when 99Mo concentrations in urine and faeces had attained plateaux (days 11–14), stable Mo and 99Mo balance trials were conducted; samples of blood and rumen contents were taken principally for studies of Mo distribution.

2. Increases in S intake caused the following changes in Mo metabolism; absorption decreased, urinary and faecal endogenous excretion decreased and retention increased; Mo concentrations in rumen contents decreased but the predominant association with the solid phase was unaffected; Mo concentrations in plasma decreased, but a higher proportion was associated with the protein fraction; Mo in protein-free plasma became apparently less ultrafiltrable at the glomerulus.

3. The pattern of response to S for each factor was generally curvilinear, the first increment in S intake having by far the greatest effect. The effect of S was generally greatest at the higher Mo intake.

4. It is suggested that the manifold effects of S on Mo metabolism are related to a common interaction in the rumen leading to the formation of Mo-complexes, possibly thiomolybdates, which are poorly absorbed but even more poorly excreted.

1. A comparative study was made of two biological techniques for assessing protein quality in wheat and barley, and in a soya-bean-protein isolate both as received, and after being heat damaged by autoclaving. Amino acid digestibility was determined by the ‘ileal’ analysis technique while amino acid availability was measured in growth assays. Some chemical and microbiological tests were also done.

2. Heat treatment of the soya-bean-protein isolate caused little change in amino acid composition but the digestibility of all amino acids and the availability of lysine and methionine were severely reduced, lysine being most affected. The reduced availability of lysine was not entirely attributable to impaired digestibility.

3. The amino acids in wheat and barley were highly digestible. The availability of methionine and lysine in barley and of methionine in wheat was high, whereas the availability of lysine in wheat was apparently much lower.

4. The results showed that for methionine, digestibility values are a fair measure of the availability. In heat-damaged soya-bean-protein isolate however, digestibility of lysine over-estimated the availability, indicating that amino acid digestibility may sometimes provide a misleading indication of nutritional value.

1. The food intake, pancreas weight and trypsin (EC 3.4.21.4) and α-chymotrypsin (EC 3.4.21.1) activities in the pancreas were measured in rats during pregnancy and lactation and after the young were weaned.

2. All the quantities measured increased significantly during lactation and had returned to their original values by 4 weeks after weaning. Food intake and pancreas weight were highest after the second week of lactation. Total trypsin and α-chymotrypsin activity, and the activity per g tissue, fell during pregnancy and rose during lactation, reaching a maximum I week after weaning.

3. From these and other results it is suggested that the hypertrophy and hypersecretion of pregnancy and lactation are initiated by changes in insulin secretion and mediated by the trophic effects of gut hormones, and that differences in the nature and timing of the response may be controlled by nutrient availability.

1. Digesta were collected from twenty-three pigs, initially of 30 kg live weight, and fitted with single Ash re-entrant cannulas in either the duodenum, jejunum or ileum. A further twenty-four pigs were used in a conventional digestibility trial.

2. Three approximately isonitrogenous diets were used; they contained: barley, fine wheat offal, white fish meal, minerals and vitamins (diet BWF), starch, sucrose, maize oil, cellulose, minerals, vitamins and either groundnut (diet SSG) or casein (diet SSC).

3. The flow-rates of nitrogen (N), liquid-fraction N (LN) and non-protein liquid-fraction N (NPLN) were measured hourly in the duodenum and jejunum and every 6 h in the ileum during 24 h collection periods. Faeces were collected during 5 d periods.

4. Marked increases in flow of N, LN and NPLN were seen in the duodenum and jejunum after feeding each diet, but not in the ileum.

5. Values for, N output: intake from the duodenal, jejunal or ideal cannulas and in faeces in 24 h periods were respectively: 0.98, 0.88, 0.25 and 0.21 for diet BWF; 1.00, 0.97, 0.22 and 0.24 for diet SSG; 0.98, 0.73, 0.09 and 0.03 for diet SSC. The corresponding values for LN in the duodenum, jejunum and ileum respectively were: 0.53, 0.53 and 0.12 for diet BWF; 0.46, 0.60 and 0.13 for diet SSG; 0.57, 0.50 and 0.06 for diet SSC. The corresponding values for NPLN in the duodenum, jejunum and ileum respectively were: 0.41, 0.38 and 0.09 for diet BWF; 0.35, 0.36 and 0.08 for diet SSG; 0.46, 0.38 and 0.04 for diet SSC.

6. The results are discussed in relation to similar studies, particularly in pigs with duodenal cannulas, in which widely different observations were made.

1. Digesta were collected from seventeen pigs initially of 30 kg live weight fitted with single re-entrant cannulas in either the duodenum, jejunum or ileum. A further twenty-four pigs were used in a conventional digestibility trial.

2. The pigs received three types of diet containing: barley, fine wheat offal, white fish meal, minerals and vitamins (diet BWF); starch, sucrose, maize oil, cellulose, minerals and vitamins and either groundnut (diet SSG) or casein (diet SSC).

3. Amino acids were measured in samples representative of the digesta flow in 24 h periods and in the faeces collected in 5 d periods.

4. For each diet the total flow in 24 h periods in the duodenum for aspartic acid, threonine, serine and glycine exceeded or equalled intake, while the amounts of the other amino acids were usually rather less than intake.

5. For each diet in the jejunum, the amounts of glycine and cystine exceeded intake in 24 h periods, while methionine, arginine and tyrosine were the most rapidly absorbed amino acids anterior to the cannula site. On average 0.22, 0.25 and 0.31 of the dietary amino acids were absorbed anterior to the cannula site for diets BWF, SSG and SSC, respectively.

6. For each diet in the ileum, the least apparently absorbed dietary amino acids were glycine and cystine. On average 0.81, 0.83 and 0.95 of the dietary amino acids were absorbed anterior to the cannula site for diets BWF, SSG and SSC, respectively.

7. There was net disappearance of most amino acids in the large intestine, but some net accumulation occurred in this region.

8. The results are discussed in relation to the amino acid composition of endogenous secretions (particularly glycine in bile), protease and peptidase specificity, free amino acid absorption and the role of the microflora in the large intestine.

1. A study has been made of the zinc, copper, iron, manganese, protein (nitrogen x 625) and phytic acid contents of nineteen soya-bean-based textured-vegetable-protein (TVP) meat-extenders and meat-substitutes and of three ‘ready-prepared’ canned meals containing TVP.

2. Phytate analysis was performed using a newly-developed method based on Holt's (1955)procedure. This method enabled the phytate content of milligram quantities of TVP to be estimated, with an SD for six replicates of 3%.

3. The Fe, Cu and Mn contents (mg/kg) of the meat-extenders or meat-substitutes varied, wzith values of 59.4–144, 14.1–19.7 and 19.5–29.1 respectively. The protein content of these products was approximately 500 g/kg.

4. The phytate content of the meat-extenders and meat-substitutes ranged from 11.0to 20.2 g/kg and the Zn content from 35.0 to 49.4 mg Zn/kg. The calculated molar ratio, phytate:Zn varied from 25 to 42.

5. The trace element, phytate and protein contents of the ‘ready-prepared’ canned meals were 30–50 %: lower than the meat-extenders and meat-substitutes.

6. Cooking the ‘ready-prepared’ meals as specified by the manufacturers was without effect on the trace element or phytate content.

7. When TVP was fed to rats as the only protein source, they had significantly lower growth rates and plasma Zn concentrations than rats given an egg-albumen-based diet of similar Zn content (14.5mg Zn/kg). Supplementation of the TVP diet with Zn (100 mg Zn/kg) significantly increased growth rate and plasma Zn concentration whereas Zn supplementation of the albumen diet was without effect.

8. The possible implications of consumption of TVP products in relation to Zn status of the human population is discussed.

The stability of potassium tetrathiomolybdate was studied in vitro using solutions with molybdenum, hydrogen ion and phosphate concentrations similar to those normally found in the rumen. Under these conditions K2[MoS4] hydrolysed rapidly and as a result the solution contained [MoS4]2−, [MoOS3]2−, [MoO2S2]2−, [HS]− and H2S in equilibrium. In view of this hydrolysis, in vivo studies of thiomolybdate on copper metabolism of sheep should not exclude the possibility that either sulphide or molybdate is responsible for any observed effect.