1. The efficiency of production and utilization of vitamin B12 was studied with sheep given a cobalt-deficient diet with and without supplementary Co (1 mg/d). Vitamin B12 to lignin ratios in rumen contents were used to estimate minimum rates of production and these were related to faecal and urinary excretion. Tissue distribution and excretion of vitamin B12 were studied with [58Co]cyanocobalamin and 5′-deoxyadenosyl[60Co]cobalamin.

2. Labelled Co was rapidly sequestered by particulate material in the rumen and was largely excreted in the faeces. Most of the vitamin B12 in whole rumen contents was contained in micro-organisms, but was released on incubation at pH 2. Added cyanocobalamin was partly degraded in the rumen.

3. The vitamin B12 to lignin ratio in rumen contents began to decline 1–3 d after cessation of a daily Co drench. Estimated ruminal production of vitamin B12 on full feed was not less than 400–700 μg/d with supplementary Co and 50–110 μg/d from the Co (0.01–0.05 μg/g dry weight) in the basal diet. Production of vitamin B12 appeared to be limited by food intake with or without additional Co.

4. At full feed the efficiency of production of vitamin B12 from Co in the basal diet was about 13% while that from added Co was about 3%. Part of the vitamin B12 produced in the rumen was degraded before reaching the faeces and about 5% was absorbed. The minimum total requirements of sheep for vitamin B12 are assessed at about 11 μg/d.

5. Injected 5′-deoxyadenosylcobalamin was better retained than injected cyanocobalamin, faecal excretion exceeded urinary excretion with both. Labelled cobalamin was selectively retained by liver (particularly by the mitochondria), kidneys and the walls of parts of the alimentary tract. Vitamin B12 was secreted into the duodenum and reabsorbed in the ileum, but little secretion occurred above the duodenum and little absorption below the small intestine.

1. Studies were made with pair-fed vitamin B12-deficient and vitamin B12-treated or cobalt-treated ewes fed a Co-deficient diet in cages. Measurements were made of body-weight changes and some observations were made of energy and nitrogen metabolism. The effects of oral Co on energy and nitrogen metabolism were examined in sheep fed the Co-deficient diet, but not yet deficient of vitamin B12 in the tissues.

2. The rate of loss of body-weight of vitamin B12-deficient sheep was significantly faster (P<0.01) than that of pair-fed sheep given 50 μg vitamin B12/d by injection.

3. In a limited number of observations of pair-fed sheep no significant differences were found in retention of combustible energy from the diet, but excretion of faecal nitrogen was higher in deficient animals than in animals receiving vitamin B12 or Co.

4. There was no significant effect of supplementary Co on energy metabolism, nitrogen metabolism, production of methane or digestibility of fodder in sheep that were not deficient of vitamin B12.

1. Feeding on a raw soya-bean diet (RSD) increased the levels of trypsin, chymotrypsin and pancreatopeptidase E but decreased the level of amylase in the pancreas of chicks as compared to a heated soya-bean diet (HSD), while supplementation of HSD with soya-bean trypsin inhibitors increased the activity of all four enzymes. HSD + trypsin inhibitors caused significant enlargement of the pancreas but only a slight depression in growth rate.

2. Fasting for 24 h of chicks previously given RSD and HSD increased the activity of all four enzymes but the increase was much greater in chicks previously given RSD than in those previously given HSD.

3. Feeding RSD for 4 d to chicks previously adapted to HSD resulted in a dramatic inhibition in growth rate, a small increase in pancreas weight, and an increase in the activity of all proteolytic enzymes, while no change in the amylase was detectable.

4. Trypsin, chymotrypsin and pancreatopeptidase E activities were assayed in the contents of the small intestine and caecum of chicks fed on RSD or HSD over a period of 35 d. Trypsin and chymotrypsin activities in the small intestine were lower in chicks fed on RSD while pancreatopeptidase E activity was almost equal or even higher in RSD-fed chicks, especially at the age of 35 d. Trypsin activity in the caecum of RSD-fed chicks was lower at all stages of the experiment, while the pancreatopeptidase E and chymotrypsin activities in the caecum of RSD-fed chicks exceeded the levels in the HSD group at the age of 21 and 35 d respectively. It would appear therefore that pancreatopeptidase E may play an important part in overcoming the inhibition of the proteolytic activity in the intestine of chicks fed on RSD.

1. Metabolism of urea in non-pregnant and pregnant sheep (1–25 d from term) has been examined. Injections of [14C]urea were used to estimate urea entry rate, urea pool size and urea space in sheep given 1000 g of a diet of equal parts of crushed oats and chaffed lucerne hay (day a) and in the same sheep 4 d after the ration had been reduced to 250 g (day b).

2. On both experimental days (a and b), mean pool size was greater (14% on day α, 29% on day b) and urea space was greater (54% on day α, 24% on day b) in pregnant animals than in non-pregnant animals; mean plasma urea concentrations were lower (35%) in the pregnant animals on day a but were not significantly different on day b.

3. The entry rate of urea was similar in all the animals on day a, but was significantly higher (34%) in pregnant than in non-pregnant animals on day b. There was a significant decrease in urea entry rate in both pregnant (33%) and non-pregnant (86%) animals on day b.

4. The rate of excretion of urea was lower (26% on day a, 35% on day b) in pregnant animals, indicating a higher (31% on day α, 40% on day b) rate of degradation of urea in the digestive tract of pregnant as compared with non-pregnant sheep.

5. Measurements of urea entry rate have been used to calculate the upper limit of amino acid deamination in pregnant and non-pregnant sheep, and this has been used as an indication of the potential availability of amino acid carbon for glucose synthesis. It is suggested that, at a maximum, amino acids may have contributed the carbon required for 63 g/d and 52 g/d of glucose on days a and b respectively.

1. The metabolism of tritium-labelled tocopherol was investigated in thirty-six wethers and forty-two ewes fed on hay known to produce nutritional muscular dystrophy (NMD).

2. In one experiment, the effect of selenium or vitamin E or both on the metabolism of tritium-labelled tocopherol was studied. No difference was found in the incorporation rate of radioactivity in tissues due to the addition of either of these components.

3. In a second experiment, significantly more radioactivity was found in the tissues of sheep dosed intramuscularly than of those dosed by stomach tube into the rumen. Excretion of radioactivity was rapid when labelled tocopherol was given into the rumen.

4. In a third experiment, the efficiency of vitamin E in preventing NMD in lambs was tested. Supplementation with vitamin E of the diet consisting of NMD-producing hay and given to ewes was ineffective as a prophylactic treatment. Direct administration of vitamin E to the lambs completely prevented the occurrence of NMD. Plasma vitamin E concentrations in the treated lambs were significantly higher than in untreated lambs at weekly sampling over a 4-month period regardless of whether the lambs were born from ewes treated with the vitamin or not.

1. Eight groups of ten weanling rats were maintained for 60 d on diets containing calcium and phosphorus in the ratio 1:1 (w/w) at four different levels of mineral, namely 0.08, 0.12, 0.24 and 0.36% Ca, with and without the addition of ergocalciferol.

2. Provision of vitamin D increased final body-weight except at the highest level of mineral intake. Similarly, increasing the mineral intake increased final body-weight except at the highest level.

3. Vitamin D raised the serum Ca concentration at all levels of mineral intake but in the experiment as a whole had no significant effect on serum P concentration. Serum Ca concentration was significantly higher at the two higher levels of mineral intake than at the two lower levels. Increasing dietary mineral caused a progressive increase in serum P concentration, except at the highest level of intake.

4. In general, the addition of vitamin D to the diets had no effect on the fresh or dry weights of the humeri; there was an indication, however, that at the two lower levels of mineral intake, vitamin D reduced the fresh weight of bone. The addition of the vitamin caused a reduction in bone volume, and an increase in bone length, bone ash and the ratio of the weight of ash to the weight of organic matter in dry, fat-free bone. With increasing dietary mineral there was an increase in the value of all the bone measurements except bone volume, which was decreased.

5. The addition of vitamin D and increasing dietary mineral both caused an increase in tooth mass and ash content.

6. The ratios of tooth mass to bone mass, and tooth ash to bone ash were unaffected by vitamin D, but decreased with increasing mineral intake.

7. Histological examination of the bones showed that the animals receiving 0.08 % of Ca and P were markedly rachitic although the presence of vitamin D ameliorated the condition. When the dietary mineral intake was raised to 0.12% Ca and P the animals were less severely rachitic and in the presence of vitamin D the bones appeared normal.

8. The incisor teeth were abnormal at the two lower levels of mineral intake, but when vitamin D was provided, the histological appearance was improved. When the Ca and P level in the diet was 0.24%, the incisal dentine appeared normal but the apical predentine was slightlywider thannormal; addition of vitamin D produced teeth of normal appearance. The incisor teeth were normal in appearance in the remaining groups.

9. These results are compared with those obtained in two previous studies where the Ca to P ratios were 1:10 and 10:1 (Harrand & Hartles, 1968, 1969).

1. S 24 perennial ryegrass was harvested at six stages of its growth from young leafy herbage to mature grass in which the seed had shed.

2. Two sheep were offered 1kg/d of each cut and two other sheep were offered 750 g/d of each cut of grass.

3. The contents of some possible precursors of the urinary aromatic acids excreted by sheep, namely, shikimic acid, quinic acid, chlorogenic acid, total o-dihydroxyphenolic compounds, lignin and crude protein were determined in each cut of grass.

4. A gas-liquid chromatographic method for the determination of the aromatic acids present in light petroleum extracts of urine was developed.

5. The urinary excretion of creatinine, diethyl ether-soluble acids, hippuric acid, total benzoic, phenylacetic and phenylpropionic acids, and the apparent digestibilities of nitrogen, lignin and dry matter were determined with each sheep offered each cut of grass.

6. The quantity of the various aromatic acid fractions excreted by sheep decreased as the maturity of the herbage increased and was directly proportional to the amount of food consumed.

7. No relationship was found between the intake of possible benzoic acid precursors and the urinary excretion of benzoic acid. With diets of young herbage, smaller amounts of benzoic acid were excreted in the urine than would be predicted from the intakes of the precursors studied, and with mature herbage greater amounts were excreted than would be predicted.

8. Possible reasons for these results are discussed, and the nature of additional precursors of urinary aromatic acids excreted by sheep given mature herbages are considered.

9. Urinary excretion of phenylacetic acid varied with diet in a manner which closely followed the intake of apparently digestible nitrogen. A highly significant (P < 0.001) exponential relationship was found between these two variables; it was log10 E = 0.05 N –0.63, where E is the urinary phenylacetic acid output (g/kg food) and N the intake of apparently digestible nitrogen (g/kg food).

1. Two experiments were carried out with sheep and cattle receiving high-concentrate rations to estimate the amount of digestion taking place in the rumino-reticulum and omasum. Two techniques were used for the collection of samples of abomasal contents. In the experiment with sheep, animals were slaughtered at different times after feeding and samples of digesta were collected. In the experiment with cattle, samples were collected through an abomasal fistula at 2 h intervals throughout the entire 24 h. Chromic oxide powder was incorporated into the ration.

2. Digestion of DM in the rumen estimated by the chromic oxide ratio ranged from 36 to –7%. Estimates based on the lignin ratio ranged from 57 to 68%. Estimates based on lignin as the marker were more consistent within experiments.

3. Starch digestion in the rumen based on the chromic oxide ratio ranged from 56 to 92% while estimates based on the lignin ratio ranged from 89 to 96%. The amount of starch digested, according to chromic oxide ratios, was up to 500 g more than estimated organic matter digested in sheep, and up to 2 kg more than organic matter digested in cattle, both impossible results. Estimates based on lignin were always less than estimated dry-matter digestion.

4. In view of the untenable results obtained by using chromic oxide powder mixed in the ration as an indigestible marker, while lignin in the same samples always yielded credible results, it appears that chromic oxide is not always a suitable marker for estimating rumen digestion from abomasal samples.

1. By feeding safflower-seed oil to rats deficient in the essential fatty acids it was found that major changes in the liver and serum triglycerides had occurred in 4 d although the fatty acid composition had not fully returned to normal.

2. Rats which had been on a saturated-fat diet for 18 weeks were given for 4 d, a diet supplemented with safflower-seed oil, methyl linolenate or ethyl arachidonate. Linoleic and linolenic acids failed to reduce the liver triglycerides but had some effect in raising the serum triglycerides to normal. Arachidonic acid reduced liver triglycerides but had no effect on serum lipids. There were marked changes in the fatty acid composition of the phospholipids but little change in the triglycerides.

3. There was good correlation between the concentrations of the phospholipids and the triglycerides in the serum. The concentration of serum phospholipids was positively correlated with the percentage of linoleic and arachidonic acids but negatively correlated with the percentage of palmitoleic, oleic and 5, 8, 11-eicosatrienoic acids.

4. In a further 4 d feeding experiment in which the lipoprotein fraction of very low density from the serum was measured, it was found that safflower-seed oil led to an increase but methyl arachidonate resulted in a decrease in the concentration of the lipids.

5. Extraction of the lipoprotein fraction of very low density from normal and deficient rats with n-heptane at – 18° indicated that phosphatidyl cholines containing stearic acid and either arachidonic or 5, 8, 1 1-eicosatrienoic acid were the most firmly bound.

6. It was concluded that linoleic acid and arachidonic acid had different and specific roles in lipid metabolism.

1. Three factors were investigated which influence blood urea content, namely the protein content in the diet, the time after feeding and the protein quality of the diet.

2. To investigate the relationship between the protein content in the diet and the blood urea content, seventeen experiments with rats given increasing amounts of protein in the diet were carried out. The experimental results show that there is a positive correlation (r = 0.95) between the protein content in the diet and the blood urea content.

3. For investigation of the influence of time after feeding on the urea content in the blood, a pig was used having a catheter in the portal vein for blood sampling at intervals. The results from this experiment showed that the blood urea content increases for the first 3–4 h after feeding and thereafter reaches a plateau.

4. To use blood urea measurement as a technique for assessing protein quality it is necessary to work under standardized conditions, especially in regard to the two factors just discussed.

5. Forty-two feeding-stuffs of widely differing quality were used in nitrogen balance trials with rats. The results showed that there is an inverse relation between the blood urea content and the biological value of the diet which is sufficiently accurate (coefficient of variation = 53%) to provide ausefulmethod for the predictionof protein quality from measurement of urea levels.

1. Techniques for the preparation of a semi-synthetic basal diet suitable for the rapid production of zinc deficiency in the rat are described. The complete diet usually contains between 0.6 and 0.9 ppm Zn.

2. When the unsupplemented diet was fed to weanling rats, growth arrest occurred after 4–5 d; when supplemented with ZnSO4 to provide 12 or 20 ppm Zn, the rate of growth of rats was similar to that attained in animals given a conventional stock colony diet providing 83 ppm Zn. A study of relationships between dietary Zn concentration and weight gain in 21 d suggested that the Zn requirement of male and female rats for growth on this diet is approximately 12 ppm.

3. The development of Zn deficiency on diets providing < 1 or 3 ppm Zn was accompanied by poor food consumption and the development of a characteristic cyclic pattern of intake. A significant decline in the variability of daily food intake was observed when the diet was supplemented with Zn to provide 6, 9 or 12 ppm.

4. Studies of the influence of dietary Zn content upon changes in the Zn content of a range of tissues and upon whole-body Zn retention are reported.

5. The above findings are discussed in relation to the problem of defining the severity and duration of Zn deficiency in animals used for studies on the nature of the metabolic role of Zn.

1. In an attempt to elucidate the pathogenic mechanism of the fatty liver of kwashiorkor some aspects of lipid metabolism were studied in ten patients with kwashiorkor and nine with marasmus, so classified according to the clinical and laboratory findings.

2. Plasma lipid levels, especially those of triglycerides, were low in patients with kwashiorkor; they showed a marked rise very early during treatment.

3. The changes in the plasma lipid levels occurred mainly in the serum lipoprotein fraction of density < 1.063. The elevation of plasma lipid levels during treatment coincided with a loss of liver lipids and a marked rise in serum protein concentration.

4. The findings support the suggestion that the primary mechanism in the production of the fatty liver of kwashiorkor is an impairment in the synthesis of lipoprotein of very low density, probably due to the rate-limiting synthesis of its protein moiety.

5. In patients with marasmus no modifications in lipid metabolism were detected by the methods used.

1. Pelleted diets containing concentrates and 0, 20, 40 or 60% chopped straw were fed ad lib. for 5 h daily to four cows. Voluntary intake, digestion and rate of passage of these diets were examined, and also the behaviour of the cows and the amount of material in the rumen before and after feeding.

2. Least dry matter (7.5 kg) was consumed when there was no roughage in the diet. When roughage was present, its level had no effect on dry-matter intakes, which were 10.7, 11.3and 10.7kg for 20, 40 and 60% roughage respectively. Digestible energy intakes were greatest with diets containing 20 or 40% roughage.

3. The digestibilities of the dry matter of the four diets were 81, 69, 59 and 55% in increasing order of roughage content. The proportion of total digestion which occurred in the rumen decreased as the roughage content of the ration increased. The rate of breakdown of cotton threads in the rumen increased as the roughage content of the diet increased.

4. Rates of passage varied greatly between cows and there were no differences between treatments in passage rates through the entire alimentary tract. The diets on which the cows consumed the largest amounts of digestible energy (20 and 40% roughage) passed through the rumen more slowly, and through the hind gut more quickly, than the other diets.

5. The times spent daily eating and ruminating both increased as the proportion of roughage in the diet was increased, but in relation to the amount of dry matter eaten, eating times were lowest with diets containing 20 or 40% roughage. Time spent ruminating per kg straw eaten decreased with increasing straw content of the diet. Rumen contraction rate during eating was greatest when dry-matter intake was greatest, but during rumination it was similar with all three levels of roughage.

6. Before and after feeding, the amount of digesta and digesta dry matter in the rumen increased as the proportion of roughage in the diet increased. After feeding, there was a highly significant linear relationship between the amount of digesta in the rumen and the digestibility of the diet.

7. In a second experiment, similar diets containing 0 or 50% roughage were given to two cows for 5 or 24 h daily. The 24 h intake expressed as a percentage of 5 h intake was 148% for the 0% roughage diet, but only 105% when the diet contained 50% roughage.

8. The results of these experiments are interpreted as indicating a declining importance of physical factors in the regulation of the intake by cows of a range of diets of increasing digestibility.

1. In a double reversal experiment, diets containing either a normal or a large amount of lignin fibre were given to four patients with pruritus due to a liver disease.

2. Neither an improvement in symptoms nor a decrease in serum bile acid levels was found. The dose of fibre may have been insufficient, changes in intraluminal pH may have impaired adsorption of bile acids, or, less likely, the concentration of bile acids in the intestine may have been too low.

1. Physiological oral doses of DL [5-Me-3H]α-tocopherol were administered to fasting subjects with various disease states, with and without steatorrhoea, and net absorption was calculated by measurement of faecal unabsorbed radioactivity. In each subject studied more than 70% of the faecal radioactivity was excreted as unchanged α-tocopherol.

2. α-Tocopherol absorption was significantly less in subjects with steatorrhoea (mean 59.4%, range 31–83%) than in those without steatorrhoea (mean 72.4%, range 51–86%). Nineteen out of twenty-four subjects with steatorrhoea absorbed less than 65% of the α-tocopherol dose, while twenty-two out of twenty-six subjects without steatorrhoea absorbed more than 65%. There was a significant correlation between the severity of steatorrhoea and α-tocopherol absorption. In a wide range of diseases steatorrhoea appeared to be the common factor associated with a decrease in α-tocopherol absorption; however, in subjects after gastric surgery α-tocopherol absorption was often low even in the absence of steatorrhoea, and this may be an important factor in explaining the high incidence of vitamin E deficiency in such patients.

3. Radioactivity in the plasma was maximal 6–12 h after dosing. Plasma radioactivity curves were significantly lower in patients with steatorrhoea than in those without steatorrhoea, but there was considerable overlap. In some patients with severe deficiency and severe steatorrhoea there was no detectable plasma response even with considerable absorption of up to 40% of the administered dose. Three patients with severe dietary deficiency of the vitamin and no steatorrhoea also showed a decreased plasma radioactivity.

4. Three subjects were studied twice, initially when deficient in α-tocopherol and a second time after repletion with α-tocopherol acetate. There was no evidence for a compensatory mechanism to increase α-tocopherol absorption in α-tocopherol deficiency.

5. A small quantity of the administered dose (almost always less than 6%) was excreted in the urine.

1. An apparatus is described for supplying small amounts of food to rats uniformly and continuously.

2. The apparatus consists of a Perspex disc carrying a groove containing food, which is rotated once each day by an electric motor. Access of rats to the food is restricted by suitably placed baffles.

1. The effects of early zinc deficiency on DNA and protein metabolism of the liver, kidneys, testes and spleen of the young rat were studied. The investigations were carried out in two phases: before food consumption and growth were affected, and afterwards.

2. The incorporation of [3H]thymidine into DNA was markedly affected by differences of less than a week in the age of the rats.

3. Zn deficiency significantly reduced the incorporation of [3H]thymidine into DNA of liver, kidneys and spleen before growth and food consumption were affected. The degree of inhibition was of the order of 50% in the first 5 d. A similar but non-significant trend was observed for the testes.

4. The incorporation of [3C]lysine into protein was not significantly affected in liver and testes during the initial period of Zn deficiency; the incorporation into kidneys and spleen was significantly inhibited but the magnitude of the effect was only of the order of 20% in 5d.

5. One week after the start of the second phase, the concentration of DNA in liver, testes, and spleen of Zn-deficient animals was not significantly different from that in pair-fed controls. The DNA content of the kidneys was significantly reduced by the deficiency hut only to 97% of that in pair-fed animalsgiven the Zn-supplcmenteddiet. The incorporation of [3H]thymidine into DNA was not significantly different between deficient and control groups in any of the four organs investigated.

1. The effects of alterations of the protein and zinc concentrations of a semi-synthetic diet on the food intake and dietary preferences of Zn-deficient and normal rats have beencompared.

2. The voluntary food intake of Zn-deficient rats fell to 70% 96 of that of the controls. The day-to-day variation of intake increased markedly and was associated with a cyclical pattern of food consumption. When the food intake of deficient rats was slightly restricted the troughs of the cycles disappeared.

3. Concurrent with the fall in food intake, Zn-deficient rats ceased to gain weight, but a similar change was found with pair-fed controls.

4. Force-feeding Zn-deficient rats with 140 % of their voluntary intake rapidly induced signs of ill-health.

5. Reduction of the protein content of the diet from 20 to 5 % resulted in an increased food intake and the disappearance of the cyclical pattern of intake. Growth, however, was not renewed.

6. Zn-deficient rats responded to a Zn-supplemented diet within 1–2 h by an increased food intake.

7. Zn-deficient rats were able to discriminate between diets containing 6 and I ppm Zn when both diets were offered simultaneously.

8. The responses of Zn-deficient rats to Zn-containing diets did not occur if the diets did not contain protein.

1. The changes occurring in the free amino acids of the plasma of laying hens in relation to egg formation have been investigated in fed and starved hens in three experiments, each with eight birds.

2. The mean concentrations of most amino acids and of the totals were higher at night than in the morning.

3. In general, egg formation was associated with increases in the concentrations of non- essential and decreases in the concentrations of essential amino acids. Cystine and glutamic acid tended to behave like the essential amino acids.

4. After 40 h starvation seven amino acids, particularly serine, histidine and lysine, in- creased in concentration and only three, proline, ornithine and arginine, decreased significantly.

5. When eight cocks were injected with oestrogen most of the amino acids increased in con-centration. The essential amino acids (with the exception of phenylalanine), serine, proline, cystine and ornithine showed the greatest increases.

6. The results are discussed in relation to the possibility that the voluntary food intake of hens may be influenced by changes in the plasma levels of one or more essential amino acids associated with the synthesis of egg albumen. Arginine appeared to be the only amino acid that might possibly fulfil this role.

7. It was concluded that investigations of changes in the free amino acids of hen plasma are unlikely to provide a useful approach to a study of the amino acid requirements or the nutritive value of particular proteins for egg production.