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 h after giving the diet containing MHM than when any of the other three diets was given.

4. Acid secretion from the pouches for the different diets was in the order: FPC > MHM > SHM ≥ SF.

5. Protease secretion from the pouches, assayed at pH 2.1, was in the order: MHM > SHM = FPC > 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.

1. The excretion of urinary and faecal nitrogen by young Nigerian men of a low income group was found to vary significantly between subjects, but was not significantly different in the same subject, when they were given a mixed diet composed of rice, vegetables and fish on two separate occasions. At the levels of energy and protein supplied by this diet the men gained or lost small amounts of weight, mean values indicating N equilibrium, the variation around the mean being high.

2. The correlation between the urinary and faecal N of these men was significantly negative at and below the level of N equilibrium, becoming positive 2–3 weeks after they had consumed the above diet supplemented by 400 g of lean beef per day, and had already established considerable rates of gain in body-weight and N retention. The diets were made isoenergetic by adding the beef at the expense of cassava flour and red palm oil.

3. The physiological processes involved in the adaptation, by young Nigerian men of low income, to a highly efficient use of low-protein diets are discussed in relation to the biological value and true digestibility of those diets, and to the ‘safe level of protein intake’ and protein-energy ratios proposed by FAO/WHO (1973, 1975).

4. It is concluded that the protein requirements of apparently healthy men can only be established in the context of their ecological, socio-economic and nutritional backgrounds.

1. Plasma urea entry rate, urinary urea excretion and, by difference, urea recycling in the body, together with the flow of non-ammonia N through the abomasum and digestion of dry matter (dm) before the abomasum were determined in both wethers and lambs receiving cereal-starch diets supplemented with urea to give 60–120 g crude protein (N × 6.25)/kg dm.

2. Lambs excreted less urea in urine than wethers given the same diet.

3. Relationships between plasma urea entry rate or urine urea excretion rate and plasma urea concentration were different for lambs compared to wethers suggesting greater conser vation of body N by renal control in lambs.

4. Recycling of urea was not related to plasma urea concentration in wethers but was related exponentially in lambs, suggesting recycling is controlled rather than the result of simple diffusion from the blood to the gastro-intestinal tract.

5. Abomasal non-ammonia-N flow was similar for wethers and lambs and increased linearly with urea supplementation.

6. dm digestion prior to the abomasum was not significantly altered, although there was a tendency for decreased digestion of the basal diet given to lambs.

7. Maximum microbial N flow to the abomasum was estimated as 30 g N/kg organic matter (OM) fermented in the rumen.

8. This work and the literature reviewed suggested maximum net microbial production can be obtained when the diet supplies an amount of fermentable N equal to the microbial N output. It is calculated the diet should supply approximately 26 g fermentable N/kg digestible OM or 1.8 g fermentable N/MJ metabolizable energy. This corresponds to a fermentable crude protein supply varying from 65 to 130 g/kg DM as digestible OM content increases from 400 to 800 g/kg DM.

1. Supplementing a lysine-deficient diet (5 g lysine/kg) with five increments of lysine, each of 2 g/kg, resulted in increases in growth rate of Yorkshire piglets, aged between 3 and 7 weeks, up to the highest level of lysine (15 g/kg).

2. The free lysine concentration of plasma tended to increase as the dietary lysine level increased from 13 to 15 g/kg, and plasma threonine concentration decreased significantly as the lysine content of the diet was increased from 11 to 15 g/kg indicating that threonine was the second limiting amino acid in the diet.

3. Oxygen consumption and carbon dioxide production of the piglets were not influenced by supplementing the diets with lysine. The heat production was 0.313 kJ/min per kg body-weight in the 6 h experimental period.

4. Supplementation of the diet with lysine had no consistent effect on the recovery of 14C as 14CO2 from a single dose of l-[U-14C]lysine.

5. Adjustment of the determined recoveries of the tracer dose of lysine for the differences in the plasma concentrations of free lysine for the pigs receiving the graded levels of dietary lysine simplified the relationship between recovery and dietary lysine level: it was linear for the first four increments in dietary lysine and then increased sharply for the fifth increment. This indicated that a marked change in the rate of lysine catabolism occurred as the level of dietary lysine was increased from 13 to 15 g/kg.

6. The results of this experiment indicate that the piglets' requirement for lysine is between 13 and 15 g lysine/kg in a diet which contained 181 g crude protein (nitrogen × 6.25)/kg.

1. In a number of separate experiments, yeast RNA, mixtures of its constituent nucleosides, its constituent bases and ribose were administered orally to rats. In each instance, the resultant changes in the composition of body fluids were monitored using sensitive methods.

2. Ingestion of RNA (100g/kg diet) caused detectable increases in intestinal ribose, inorganic phosphate, uridine, pseudouridine, uracil, inosine, uric acid and probably other purine bases. Their accumulation did not detectably affect the rate of passage of food along the digestive tract, even though some nucleosides are known to affect gut motility.

3. Although plasma levels of uric acid and uridine were higher when RNA was administered in the diet, these changes were very slight compared with those in plasma uracil, which in some experiments were increased more than 20-fold compared with control levels (300μmol/l). Analysis of erythrocytes indicated that the internal environment of at least some cells of the body are similarly altered.

4. Analyses indicated that all dietary RNA-phosphate passed into the urine from the gut but most of the RNA-ribose was probably metabolized. Uracil and uric acid levels in the urine reflected plasma composition.

5. The effect of orally administered mixed nucleosides on blood and urine composition was similar to that of RNA, but the response to an equivalent mixture of free bases differed in several respects; cytosine, adenine and hypoxanthine appeared in urine only under these circumstances.

1. Twenty-four pigs (mean body-weight 44 kg) were used to determine the digestibilities of energy, nitrogen and amino acids in dried microbial cells (DMC) grown on methanol and in white fish meal (WFM). N utilization and the excretion of various nitrogenous compounds were also studied.

2. Semi-purified diets containing DMC, WFM or no protein source were offered at the rate of 1 kg fresh food/d. Daily N intakes were 26.5, 24.7 and 0.65 g respectively.

3. Mean metabolic faecal N determined with the protein-free diet was 1.11 g/d (1.26 g/kg dry matter (dm) eaten) for the two experiments. The corresponding endogenous urinary N value was 2.91 g/d.

4. Daily urinary N output of pigs given the diet with WFM was significantly greater than that of pigs given the diet with DMC, with the result that N retention, net protein utilization and biological value were higher for pigs given DMC.

5. Apparent and true digestibility of amino acids were higher for the diet with DMC than for the diet with WFM.

6. N excretion in the form of ammonia, urea, uric acid and allantoin accounted for 81, 91 and 99% of the total N excreted by the groups given the protein-free diet, DMC and WFM respectively. Pigs given DMC excreted greater quantities of allantoin-N and less urea-N than pigs given WFM.

1. Fifty unselected consecutive cases of protein-energy malnutrition (PEM) presenting at the General Out-patient Clinic of the University College Hospital, Ibadan were classified as marasmus (twenty), kwashiorkor (nineteen) marasmic-kwashiorkor (seven) and undernutrition (four) according to the Wellcome Classification of PEM (Lancet, 1970; Waterlow, 1972).

2. The mean age of the children with marasmus (22.4 months) and of the children with kwashiorkor (25.4 months) were not significantly different. The children with marasmickwashiorkor (27.8 months) were significantly older than the children with marasmus.

3. The deficits in weight- and length-for-age were similar to values previously reported (Waterlow, 1972) even though the children with marasmus tended to be older and the children with kwashiorkor younger than has been reported. Values obtained for the deficit in length-for-age suggested that the children with marasmus had been undernourished from birth whereas the children with kwashiorkor had apparently grown normally until they were 10 months old. It is possible that the history of growth in the first year of life influences the final form of PEM in these two groups of children.

4. Forty-nine of the fifty children had been breast-fed for at least 9 months and nine children had been breast-fed for 2 years. Of the twenty children with marasmus nine were still receiving some breast milk. The diets fed to weaned children with marasmus and to children with kwashiorkor were identical and consisted solely of a maize-starch gruel with no supplementation of protein or vitamins. The similarity in the dietary histories of the two main groups of children suggests some uncertainty concerning a specific role for protein deficiency in the development of kwashiorkor.

5. All the children had had similar infections. The most common of these were measles (morbilli) (40% of all cases) and gastrointestinal infections. However the children with marasmus had a history of chronic diarrhoea whereas the children with kwashiorkor had had more acute diarrhoea.

6. The similar dietary histories but dissimilar histories of infection given by the mothers of the children with marasmus as opposed to those with kwashiorkor suggest that recurrent diarrhoea was at least partially responsible for the chronic undernutrition in the group of children with marasmus. Furthermore although the weaning diets were inadequate the final deterioration in nutritional status was precipitated by gastroenteritis, often following measles.

1. Preruminant calves, fistulated in the abomasum 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.

1. Lipolytic and proteolytic activities and pH values were determined in secretions collected from innervated abomasal pouches and in abomasal contents from preruminant calves given liquid diets.

2. No lipolytic activity was detected in pouch secretions collected during 1 h after feeding, though lipolytic activity was present in abomasal contents; pepsin (EC 3.4.23.1) and rennin (EC 3.4.23.4) were present in both pouch secretions and abomasal contents. The pH values of pouch secretions ranged from 1.2 to 1.8 and those of abomasal contents from 4.2 to 5.9.

3. When diet was placed directly into the abomasal pouch soon after feeding, the pH values of pouch and abomasal contents decreased similarly (i.e. from 6.3 to approximately 5). Protease activity (U/ml) of pouch contents ranged from 0.1 to 0.8 and that of abomasal contents from 0.1 to 0.2. No lipolytic activity was detected in pouch contents, though abomasal contents contained 0.6 to 1.2 U/ml and when the diet contained milk-fat as the dietary fat source considerable lipolysis of triglycerides containing shorter-chain fatty acids was found.

4. It is concluded that there is no significant secretion of lipolytic enzymes by the fundal mucosa and that the lipolysis of triglycerides in the abomasum of the preruminant calf is due predominantly to a lipolytic enzyme in saliva.

1. Nutritional evaluation of dried tomato pomace (DTP-20) as a source of protein was carried out using weanling rats. Comparisons were made with casein (CS), soya-bean meal (SOM-45) and the hydrocarbon-grown yeast Toprina (BP-T). The growth-promoting effects of the diets were evaluated over a period of 28 d of ad lib. feeding.

2. The unsupplemented DPT-20 had a protein efficiency ratio (per) of 2.18±0.13 and a net protein utilization (npu) of 0.55. The addition of dlmethionine (5 g/kg) resulted in a per of 1.74±0.15 (t 2.99, P < 0.01) and a npu of 0.40, while the addition of an amino acid mixture resulted in a per of 2.33±0.08 (t 1.84, P < 0.1) and a npu of 0.70.

3. The reason for the decrease in growth and the reduced per and npu values recorded for the methionine-supplemented group of rats is not clear and it is discussed in connexion with an imbalance or a slight toxicity caused by the added amino acid.

1. Food intake, and the rates of protein, lipid and energy deposition during growth were measured for lean and congenitally obese (fatty) female Zucker rats given diets of different protein content ad lib. Six semi-synthetic diets were used, which contained 40, 100, 150, 300, 500 and 700 g casein/kg (diets 40C, 100C, 150C, 300C, 500C and 700C).

2. Dietary treatments began when the rats were 34 or 35 d old. Collections of urine and faeces were analysed for energy content. The total carcasses of all the rats were analysed individually for protein, lipid and energy.

3. In the first experiment, twelve rats of each phenotype were given diets 150C or 300C. Four fatty and four lean rats were killed at 50, 66 and 98 d of age. In the second experiment groups of four fatty and four lean rats were given diets 40C, 100C, 500C and 700C ad lib. until they were killed at 66 d of age. Other groups of fatty rats were pair-fed from 35 to 67 d of age on diets 100C and 500C. Rats were also killed at 24 and 34 d of age to provide initial samples for the comparative slaughter procedure.

4. When given food ad lib., fatty and lean rats had identical rates of protein deposition at all ages and for all diets, but lipid and energy deposition were always much greater in the fatty rats. Food intake was also much greater for the fatty rats (except on diet 40C). Differences in food intake and growth rate attributable to diet were most pronounced for the range of diets 40C-150C.

5. Fatty rats pair-fed to lean rats deposited less protein but about twice as much energy and lipid as lean rats on the same diets.

6. The results are discussed in relation to existing theories of appetite control. It appears that food intake is precisely regulated in the congenitally obese Zucker rat. This regulation is intimately linked with the impetus for protein deposition and the rates of retention of lipid and energy appear to be of no importance in relation to appetite control.

1. The digestibility of the cell wall polysaccharides of an alkane-grown yeast in different parts of the digestive tract of two veal calves fitted with re-entrant cannulas at the end of the ileum was studied by replacing part of the skim-milk powder of their ‘normal’, milk-substitute (all-milk-protein) diet by yeast (yeast diet).

2. The lactose and glucose of both the all-milk-protein diet and the yeast diet were almost completely digested before the end of the ileum. During this digestion a small amount of oligosaccharides composed of galactose and glucose was synthesized. These oligosaccharides were digested again in the large intestine.

3. The constituent sugars of the water-soluble fraction of the yeast cell wall carbohydrates were glucose and mannose. The 0.5 m-sulphuric acid-hydrolysate of the water-insoluble fraction contained glucose and mannose and the 12 m-H2SO4-hydrolysate only glucose.

4. Digestibilities of these fractions over the whole gastrointestinal tract ranged from 0.77 to 0.90. Digestibilities measured at the end of the ileum varied considerably between the two animals and averaged only about 0.40.

5. These findings suggest that the cell wall polysaccharides of yeast are digested very little by the normal digestive enzymes of the calf's small intestine, but are used as a substrate by the bacterial flora which are mainly concentrated in the large intestine.

1. Five groups of juvenile turbot (Scophthalmus maximus) which had been given a diet free of fat for 12 weeks were given diets in which the lipid component (g/kg) was: oleic acid alone 50, oleic acid 40+linoleic acid 10, oleic acid 40+linolenic acid 10, oleic acid 40+arachidonic acid 10 or oleic acid 40+cod-liver oil 10. These five experimental diets were given for 16 weeks.

2. Weight gains were highest in the group given the diet containing cod-liver oil and lowest in the groups given diets containing oleic acid alone or oleic acid+linoleic acid. Weight gains in the groups given oleic acid+arachidonic acid or linolenic acid were markedly inferior to those of the group given oleic acid+cod-liver oil. It is concluded that arachidonic acid is inferior to polyunsaturated fatty acids of the ω3 series in maintaining growth rate in turbot.

3. Fatty acid analyses of neutral lipids and phospholipids of liver and extrahepatic tissues did not suggest any evidence of desaturation of dietary oleic acid, linoleic acid or linolenic acid by the turbot. These experiments confirm previous isotopic evidence that turbot lack the necessary microsomal desaturases to perform this metabolic transformation.

1. The adoption of a meal-eating pattern of feeding by rats altered the alkaline phosphatase (EC 3.1.3.1) activity in serum and liver. It was therefore necessary to regulate the feeding pattern of both magnesium-deficient rats and control animals receiving a Mg-adequate diet in order to study the effect of the deficiency.

2. Mg deficiency decreased the activities of alkaline phosphatase and inorganic pyro-phosphatase (EC 3.6.1.1) in serum, kidney and tibia, but increased them in spleen.

3. Addition of a standard concentration of exogenous Mg to tissue extracts usually increased the activity of corresponding enzymes from Mg-deficient and control rats by the same proportion, indicating that the main effect of the deficiency was on the amount of enzyme present rather than on the efficiency of its operation.

4. Certain quantitative differences in the response to exogenous Mg and the activity ratio, alkaline phosphatase: inorganic pyrophosphatase were found between tissues from Mg-deficient and control rats. The significance of these are discussed in relation to the association of the two enzymic activities with the same protein molecule, and the possible occurrence of isoenzymes.

1. Thirty-five pigs were 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. Methods for collecting, sampling and returning digesta were developed.

3. A ‘practical-type’ diet and two purified diets were used, fed twice daily.

4. Flow and pH of digesta were measured hourly in the duodenum and jejunum, and every 6 h in the ileum.

5. In the duodenum and jejunum there were clear flow responses to feeding, while such an effect was not found in the ileum where the flow-rate was much lower and more uniform than in the former sites.

6. In the duodenum and jejunum, and within 6 h periods in the ileum, there was considerable variation in the flow-rate between different pigs within each hour but there was less variation in pH.

7. The pattern of flow in the duodenum and jejunum was similar for each of the diets but the total flow and the average pH in 24 h differed significantly between diets. There were more digesta of a lower pH from the ‘practical-type’ diet than the purified diets.

8. The pH in the duodenum was highest after feeding and decreased with increasing time after feeding. In the jejunum and ileum the pH varied over a much smaller range than in the duodenum.

9. Collections for 6 h periods appeared to be insufficiently long to predict the values obtained in 24 h collections with reasonable accuracy.

1. Steers, fitted with simple rumen and duodenal cannulas, were given diets of approximately equal parts of flaked maize and hay (A) (containing 16 g nitrogen/kg dry matter (dm)) or diets of flaked maize and straw supplemented with decorticated groundnut meal (B), fish meal (C), or heated (D) or unheated (E) soya-bean meal (containing 24 g N/kg dm). Chromic oxide was given as a marker with the feeds, and flows of different combined sugars at the duo denum estimated from the values for sugars: marker at this site. Contributions of bacterial constituents to these flows were estimated from amounts of RNA present.

2. Rumen bacteria from steers receiving diet A contained approximately 110 g α-dextran-glucose/kg dm and contributed about 60 g α-dextran-glucose/d at the duodenum; bacteria from steers receiving diets B, C, D or E contained 25–40 g α-dextran-glucose/kg dm and contributed about 20–30 g α-dextran-glucose/d at the duodenum. There were no significant differences between different N supplements. About half the α-dextran-glucose, varying amounts of the mannose and galactose, and nearly all the rhamnose and ribose in duodenal digesta were contributed by the bacteria. Almost all the arabinose, xylose and cellulose-glucose was of dietary origin.

3. For steers receiving diet A, mean coefficients of digestibility between mouth and duodenum, corrected where necessary for bacterial contribution, were 0.96, 0.73, 0.58, 0.22 and 0.53 for starch-glucose, galactose, arabinose, xylose and cellulose-glucose respectively. Corresponding mean values when diets B, C, D and E were given, which did not differ significantly amongst themselves, were 0.98, 0.79, 0.81, 0.59 and 0.58. Most values for galactose, arabinose and xylose were significantly higher than the diet A values.

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.

1. The role of corticosteroids in determining which clinical features of protein-energy malnutrition develop on a deficient diet has been studied by the administration of cortisone acetate to experimentally malnourished rats fed ad lib. on a mixture containing 31 g protein/kg.

2. Daily administration of 1.25 mg cortisone acetate did not affect dietary intake, which remained the same as in saline (9 g sodium chloride/l)-injected controls. Plasma albumin concentrations, however, increased from a low value of 25.7 g/1 to 47.2 g/l and this was accompanied by an increase both in liver weight and protein content. On the other hand, the protein content of muscle decreased.

3. These changes in the protein contents of liver and muscle were associated with alterations in the corresponding free amino acid pools. The free amino acid content of muscle generally decreased, but in liver many amino acids were increased.

1. A study has been made of the effects of dietary zinc supplementation on the development of copper toxicosis in three groups each of eight 12-week-old lambs.

2. None of the lambs receiving 420 mg Zn/kg diet developed Cu toxicosis in the 24-week experimental period, compared with three in the control group receiving 43 mg Zn/kg and possibly one in the group receiving 220 mg Zn/kg.

3. Liver Cu concentrations were reduced by up to 40% in the Zn-supplemented animals, with concomitant reductions, especially in the early stages of the experiment, in the extent of liver damage, as assessed by measurement of plasma aspartate aminotransferase (EC 2.6.1.1) and arginase (EC 3.5.3.1) activities.

4. Plasma and liver Zn concentrations were increased only slightly in the lambs receiving the Zn-supplemented diets, and the only indication of possible toxic effects of the Zn supplements was the development of a slight anaemia in those animals receiving 420 mg Zn/kg diet.

5. The results suggest that the incidence of Cu toxicosis in sheep may be controlled by increasing their dietary Zn intake.