1. Iron and zinc retentions in young male rats, given 3 g starch–sucrose paste containing 120 μg Fe as FeSO4 or 139 μg Zn as ZnC12 (extrinsically labelled with 59Fe or 65Zn) and increasing amounts of Gypsophila saponins, were measured by whole-body counting. The results were compared with whole-body Fe and Zn retention from a meal containing crude or purified saponin fractions. In a separate experiment Fe retention from a meal containing Gypsophila saponins, soyasaponin I, or saponins extracted from lucerne (Medicago sativa) plant tops, was measured in older rats.

2. Results indicated that Fe absorption decreased with increasing concentration of Gypsophila saponins. This was significant at a saponin: Fe molar value of approximately 1, with maximum effect occurring at molar ratios of 4 and above, when Fe absorption was reduced by approximately 17%. Gypsophila saponins had no effect on Zn absorption from a test meal.

3. Fe absorption was similar in groups given purified or crude Gypsophila saponins at the same saponin: mineral molar value of 8, demonstrating that the ‘non-saponin’ fraction of the commercial preparation does not affect the absorption of this mineral.

4. Saponins extracted from lucerne plant tops, fed at a saponin:Fe value of approximately 8, also reduced Fe absorption from a single meal. Fe absorption from a meal containing a similar amount of soyasaponin I was not significantly different from controls.

5. These results indicate that some dietary saponins may reduce Fe absorption and hence have an adverse effect on Fe status in man and simple-stomached animals.

1. The purpose of the present study was to determine the effects of diet on the mandibles and growth centres of the long bones in the fetuses of diabetic rat dams given a normal diet compared with those given a high-protein, low-carbohydrate diet.

2. On the 9th day of gestation, the controls, groups 1 and 3, were injected with citrate buffer and given 200 and 600 g protein/kg diets respectively. Groups 2 and 4 were injected with 40 mg streptozotocin/kg body-weight and pair-fed with groups I and 3 respectively on the 200 and 600 g protein/kg diets.

3. On day 22, some dams were injected with either 45Ca or [14C]proline. Mandibles and long bones were removed and weighed and analysed for Ca content, 45Ca uptake, collagen and collagen synthesis.

4. The body-weights, and mandibular and long-bone weights of the fetuses in the diabetic 200 g protein/kg group were smaller than those of the non-diabetic 200 g protein/kg group, whereas those of the diabetic 600 g protein/kg group showed no difference from the non-diabetic 600 g protein/kg group.

5. The rate of collagen synthesis was higher in the fetuses of the diabetic 600 g protein/kg group than those of the non-diabetic group. Bones of the diabetic 200 g protein/kg group were lower in collagen content when compared with the non-diabetic group, whereas there was no difference between the diabetic and non-diabetic 600 g protein/kg groups.

6. Ca uptake and total Ca contents in the mandibles and long bones showed no difference between diabetic and non-diabetic groups fed on both diets.

7. A high-protein, low-carbohydrate diet appeared to have a certain beneficial effect on bone development of the growing fetuses from diabetic dams.

1. We have investigated the relations between changes in plasma insulin and 3,5,3'-triiodothyronine (T3), and muscle growth and protein turnover in the rat in response to diets of varying protein concentrations.

2. Young rats were fed ad lib. on a control (180 g casein/kg) diet or low-protein diets containing 80, 45 and 0 g casein/kg in four separate experiments. Measurements were made of food intakes, muscle and body-weight growth rates, muscle protein turnover in vivo, plasma insulin, and plasma free and total T3.

3. The food intakes of the 80 and 45 g casein/kg diet groups were variable, with the 80 g casein/kg diet group consuming either the same or more than the controls, and the 45 g casein/kg diet group consuming less or more than the controls. Body-weight and skeletal-muscle growth rates varied with the protein but not energy intakes, which in turn reflected both dietary composition and the food intake, with the hyperphagic 80 g casein/kg diet group of rats growing almost normally and the 0 g casein/kg diet group losing body-weight and muscle mass.

4. Changes in rates of muscle growth were accompanied by parallel changes in rates of protein synthesis and degradation, as well as parallel changes in concentrations of plasma insulin and free T3, to the extent that all these variables were highly correlated with each other.

5. Partial correlation analysis was used to separate interactions between variables. This indicated that dietary energy had no identifiable influence on muscle growth. In contrast dietary protein appeared to stimulate muscle growth directly by increasing muscle RNA content and inhibiting proteolysis, as well as increasing insulin and free T3 levels. Insulin and free T3 stimulated each other as well as muscle protein turnover; insulin stimulating the RNA activity particularly at low insulin levels, free T3 stimulating the RNA content and both hormones stimulating proteolysis.

6. These apparent relations are shown to be consistent in the main part with previous studies of the mechanism of action of insulin and T3 but the possibility cannot be discounted that other anabolic hormones not measured in these studies are involved, particularly in the apparent direct influence of dietary protein on muscle.

1. In order to examine the interaction of dietary fat and carbohydrate in the regulation of lipid metabolism, we have studied hepatic and extrahepatic lipogenesis, and adipose tissue lipoprotein lipase (EC 3.1.1.34) in rats fed on one of the following diets: a fructose-based diet containing 0 (F0) or 150 g maize oil (F15)/kg, or a glucose based diet containing 0 (G0) or 150 g maize oil (G15)/kg.

2. The rats were meal-fed on the diets for 2 weeks after which the activities of a number of hepatic ‘lipogenic’ enzymes were measured and the activity of epididymal-fat-pad lipoprotein lipase. The activities of the lipogenic enzymes were: F0 > G0 > G15 > F15. Lipoprotein lipase activity was F0 = G0 = F15 = G15. The percentage of total body fatty acid synthesis which occurred in the liver was F0 > G0 > F15 > G15.

3. We conclude that fructose-induced hypertriglyceridaemia is primarily a result of the increased hepatic synthesis rather than decreased adipose-tissue lipoprotein lipase activity.

1. Weanling Wistar rats were pair fed for 10 weeks on a purified diet containing either normal or suboptimal quantities of magnesium (960 or 80 mg/kg respectively).

2. At week 2, hypomagnesaemia was accompanied by hypertriglyceridaemia, an increase in plasma cholesterol and a decrease in high-density-lipoprotein-cholesterol in animals fed on the Mg-deficient diet. At week 10, the increase in triglycerides observed in Mg-deficient animals was less marked while the increase in total cholesterol was more important.

3. During the whole experimental period, Mg-deficient animals never showed hypertension. At week 2, mean arterial blood pressure was significantly lower in Mg-deficient rats than in their respective controls, while heart rate was significantly increased. However, hypotension accompanied by tachycardia was a transitory phenomenon which appeared only in the early phase of deficiency.

4. Vascular reactivity was studied in vagotomized anaesthetized rats after ganglionic blockade with pentolinium and atropine sulphate. The reactivity to noradrenaline was significantly higher in Mg-deficient rats compared with pair-fed controls after 2 weeks on the experimental diet.

1. The regulatory role of prostaglandins (PGs) E2 and F2a on the zinc transport rate across the jejunal segments of rats was examined by employing the Ussing chamber technique. The Zn flux rate from mucosa to serosa across jejunal segments (Jms) was 5·24 (SE 1·54) nmol/h per cm2 (n 48) and that from serosa to mucosa (Jsm) was 15·16 (SE 2·38) nmol/h per cm2 (n 48) when both sides of the segment were bathed with Ringer's bicarbonate solution containing 0·5 mM-zinc chloride and 3 mM-L-histidine.

2. When 5·0 or 50 μM of either PGE2 or PGF2α were added to the serosal side of the tissue, Jsm generally decreased and Jms generally increased, compared with controls. On the other hand, when PGE2 or PGF2α was added to the mucosal side of the tissue, Jms either did not change or increased while Jsm had a tendency to decrease.

3. The Zn uptake capacity of tissue increased significantly when PG was added to the serosal side of the tissuebathing medium, but not when PG was added to the mucosal side. The uptake capacity of mucosal Zn by jejunal segments was approximately twice that of serosal Zn.

4. When PG was included in the tissue-bathing medium, the short-circuit current, potential difference and conductance between the mucosa- and serosa-bathing media generally decreased.

5. These results suggest that (a) PGs influence Zn flux rate not by chelating Zn and carrying it across the mucosal cell membrane but by interacting with the cytosolic components, (b) it is the serosal PGs which control the Zn flux rate and (c) PGs play a part in triggering a transduction mechanism in the intestinal Zn transport process.

1. Sheep with oesophageal fistulas were sham-fed on pelleted lucerne (Medicago sativa) hay to assess the palatability of added chemicals representing the tastes of sweet (sucrose), sour (hydrochloric acid), salt (sodium chloride), bitter (urea) and umami (monosodium glutamate; MSG).

2. Plain pellets and four concentrations of each chemical were sham-fed for 30 min after 5·5 h deprivation in 5x5 Latin-square experiments following a period of adaptation feeding.

3. Sucrose, at concentrations of 15–120 g/kg air-dried pellets, depressed intakes with a linear relation between intake (I; g) and concentration (C; g/kg): I = 1001-3·42C.

4. HCl at 6·25–25·0 g/kg pellets had no effect on sham intakes but at 50 g/kg reduced them by 50% of control (P < 0·05).

5. NaCl at 50–200 g/kg increased sham intakes by 26% (P < 0·01) with no evidence of a dose-related effect.

6. Urea at 10–80 g/kg decreased sham intakes by 26·9% (P < 0·01) with no evidence of a dose-related effect.

7. MSG at 5–40 g/kg in two experiments increased sham intakes by 16·1 and 40·8% (P < 0·05). In another experiment at 1-8 g/kg there wasno significant effect.

8. When palatability and post-ingestive effects are separated by sham-feeding, the effect of added chemicals on intake may be completely different from when they are ingestednormally (e.g. NaCl and sucrose). This newly developed technique enables the palatabilityeffect of feed additives to be tested critically and economically.

1. Haematological, histological and ultrastructural findings in young chicks fed on a purified diet severely deficient in folate are reported.

2. Growth of the birds was greatly depressed and they had a macrocytic anaemia. Other haematological changes included abnormal nuclear formations in erythrocytes, numerous mitoses and hypersegmented granulocytes.

3. Megaloblasts were observed in bone marrow and their fine structure is described for the first time in an avian species.

4. Morphological changes occurred also in the liver. The parenchyma had damaged sinusoidal endothelium, inflammatory cells and no glycogen. Mitochondria were damaged and many were associated with unusual crystalline structures.

5. Chickens fed on a semi-purified diet of low folate content showed no growth depression or clinical signs of deficiency but had abnormal haematological values and morphological changes that resembled those seen in birds fed on the purified diet.

6. These abnormalities responded to dietary supplements of pteroylmonoglutamic acid in a dose-related manner and may be useful in diagnosing subclinical folate deficiency.

1. The dynamics of protozoa were studied in two groups of rumen-fistulated cattle fed on a basal diet of molasses ad lib., with oaten chaff given at 6 or 18 g/kg live weight. This diet resulted in different mixtures of protozoal species in the populations in the rumen.

2. The rumen protozoa were studied by intrarumen injections of protozoa labelled in vitro with [14CH3]choline. An indication of protozoal death and fermentation of protozoal cell residues was obtained by measuring 14C loss via the methane pool.

3. After a single injection of labelled protozoa, the decline in the specific radioactivity (μCi/g nitrogen) of the protozoal pool in the rumen indicated that first-order kinetic processes applied. Conversely the specific radioactivity of protozoa, incubated in rumen fluid, remained constant indicating no growth in vitro, presumably owing to a rapid exhaustion of essential nutrients.

4. The protozoal populations in the rumen of cattle fed on the diet with the low level of oaten chaff were mainly small ciliates; but on the higher level of chaff in the diet, the large ciliates were a higher proportion of the total protozoal population present.

5. The mean pool size of protozoa in the rumen was significantly larger and the protozoal half-life tended to be longer for cattle fed on the higher level of chaff in the diet. The apparent production rate of protozoa in cattle fed on each diet was not significantly different and there were no differences in the production rate of methane. The percentage losses of label from protozoa in the rumen via the methane pool were not significantly different on the two diets and indicated that 74% of the protozoa that were apparently irreversibly lost from the rumen could be accounted for by death and lysis in the rumen and therefore only 26% of protozoa apparently entered the lower digestive tract.

1. The objective of the present study was to determine the effects of two levels of folic acid and two levels of zinc in the diets of rats during pregnancy and lactation. It addressed, among other things, the question of whether an inhibitory effect of folic (pteroylmonoglutamic) acid on Zn absorption might result in a secondary Zn deficiency in either the dams or the pups.

2. A purified diet was given to four groups of female DNL (Norwegian) Hooded rats, before and during pregnancy and during lactation. It contained the four possible combinations of: no added folic acid or 100 μg added pteroylmonoglutamic acid/g, and 6·6 or 20·2 μg Zn/g. Pups and dams were killed on day 20 of gestation or on day 20 postpartum. Measurements of body-weights, food intakes, blood folate and tissue Zn levels were performed.

3. The group with low Zn and low folate intake had a satisfactory reproductive outcome, and there were only minor effects of the supplements on body-weights.

4. Additional folate greatly increased blood (erythrocyte and plasma) folate levels, but did not compromise tissue Zn concentrations. Zn supplementation also enhanced blood folate levels, for reasons which are not yet clear.

5. There was a moderate enhancing effect of the Zn supplement on Zn levels in the livers and kidneys of pregnant dams, and the kidneys of lactating dams.

6. If the conclusions can be extrapolated to humans, then the results provide some reassurance that a high folate intake from prenatal supplementation need not necessarily cause Zn depletion, and hence functional Zn deficiency in pregnant women and their offspring.

1. The effect of fasting on hepatic mRNA levels of seven plasma proteins was examined in the rat.

2. The levels of mRNA were measured directly in cytoplasmic extracts by hybridization to specific 32P-labelled cDNA probes.

3. Following a 48 h period of fasting, the mRNA levels of apolipoprotein E, apolipoprotein A-IV, albumin, transferrin, and transthyretin decreased by 15–30%, while apolipoprotein A-II decreased by 78% compared with non-fasted control rats. The mRNA for apolipoprotein A-I increased by 33%.

4. These findings suggest that mRNA levels in the liver following fasting are regulated independently and variations in these levels may be due to differences in transcription rates or mRNA stability.

1. It has been suggested that deconjugation of food folates with pig kidney, compared with chicken pancreas, may increase measureable folate by approximately 50% (Phillips & Wright, 1983). Therefore deconjugation with conjugases from these two enzyme sources was optimized and compared. Folate was measured microbiologically with Lactobacillus casei (ATCC 7469) as the test organism at pH 5·6.

2. Treatment for 6 h with 200 mg pig kidney/200 mg sample was compared with the conventional assay employing overnight incubation with 20 mg chicken pancreas/5 g sample. Comparison of the deconjugation systems showed chicken pancreas to be superior for peas (Pisum sativum) and beans (Phaseolus vulgaris), while there was no difference for potatoes.

3. γ-Glutamyl hydrolase (conjugase; EC 3. 4.22. 12) treatment for 2 and 20 h with pig kidney and chicken pancreas was optimized for raw potatoes and green frozen peas. Treatments with pig kidney were conducted at pH 4·6, which is optimal, and at pH 5·2. There was no significant difference between 2 and 20 h treatments at pH 5·2. Treatments with chicken pancreas were conducted at pH 6·1. Treatment for 2 h was preferred as it resulted in significantly higher measureable folate activity in peas and potatoes, and because overnight treatment can be influenced by microbial production of folate.

4. With optimal treatment conditions the source of enzymes did not significantly influence measureable folate activity. Chicken pancreas is the traditional source of conjugase in Scandinavia and was preferred for deconjugation.

5. Chicken pancreas, 20 and 60 mg, was used for deconjugation of sixteen different food samples, each containing approximately 200 ng folate. Chicken pancreas at 60 mg/sample gave significantly higher results. Further addition of enzyme did not increase the folate values.

6. A combined amylase treatment using heat-resistant α-amylase (EC 3.2.1.1) during extraction to ensure the gelatinization of the sample, and glucan 1,4-α-glucosidase (amyloglucosidase; EC 3.2.1.3), along with the incubation with chicken pancreas to complete the digestion, was shown to give a small but significant increase in folate values of starch-containing samples.

7. Folate results using the recommended procedure are given for raw potatoes, wheat bran, rolled oats, wheat flour and dark rye bread.

8. Chicken pancreas was shown to contain equally high amounts of amylases as did the α-amylase and amyloglucosidase sources. This finding may explain the relatively small benefit of a specific amylase addition.

1. The possibility of an effect of zinc on the rate of tumour cell division, mediated through a regulation of cellular cAMP concentration, was investigated in the present study in rats.

2. Dietary Zn deficiency (< 1·5 mg Zn/kg) but not Zn excess (500 mg Zn/kg) resulted in an increased cAMP concentration in transplanted hepatoma cells. Neither treatment had any effect on the cAMP concentration in regenerating liver or normal resting liver. Both the deficient and excess Zn diets resulted in a small reduction in tumour growth (not statistically significant).

3. The results seem to indicate that the relation investigated in the present study does not apply in the cell line used.

1. Dunaliella bardawil, a β-carotene-accumulating alga, has been tested as a source of retinol and β-carotene in a diet given to rats. The β-carotene in this alga is composed of about equal amounts of the 9-cis and all-trans isomers. Male weanling rats were fed on a retinol-deficient diet for 60 d. Thereafter, the rats were divided into groups and fed on a diet deficient in retinol or supplemented with retinol, synthetic β-carotene, dry alga or an algal oil-extract. Following further growth for 7 d, samples were taken for liver analyses of retinol, retinol isomers and β-carotene.

2. Liver analyses revealed a comparable content of retinol and normal conversion rates in the rats grown on the diets supplemented with synthetic or natural β-carotene. Rats fed on the alga and the algal-oil-supplemented diets accumulated 9-cis retinol in addition to the all-trans isomer. Rats fed on synthetic β-carotene, alga and algal oil had a liver retinol: β-carotene value of about 3:1.

3. These studies demonstrate the possibility of using dried D. bardawil or an oil extract of the alga as a dietary natural β-carotene supplement which satisfies the total requirement of retinol in rats.

4. Rats fed on alga or on algal oil, accumulated in the liver 9-cis β-carotene and all-trans β-carotene in a ratio similar to that present in the alga.

1. Lactose, sucrose or maltose were administered to rats by gavage together with 32PO4, and blood 32P was determined.

2. PO4 uptake into blood was increased only when lactose and PO4 were administered into the gut.

3. Weaned male rats were fed on a control diet or a diet containing 30, 60 or 120 g lactose/kg. After a 5 d period of adaptation, a 6 d P balance was carried out. After a further 24 d blood levels of PO4, and calcium and PO4 uptake by brush-border membrane vesicles prepared from the renal cortex, were determined.

4. The absorption and retention of P were higher in lactose-fed rats. Faecal P excretion decreased with increasing dietary lactose content. Urinary P excretion was lower in the rats fed on 30 and 60 g lactose/kg whereas the 120 g lactose/kg diet increased urinary P.

5. Membrane vesicles isolated from rats fed on the diets containing 30 and 60 g lactose/kg showed a higher uptake of PO4, but with the 120 g lactose/kg diet uptake was lower than with membrane vesicles isolated from rats fed on the control diet.

6. A statistically significant increase in the serum PO4 level was observed in the rats fed on the diet with 120 g lactose/kg.

7. The presence of lactose in the diet caused a stirnulatory effect on PO4 absorption and retention.

1. Young male rats were fed on diets containing 3·4, 36 or 411 mg zinc/kg for 10 weeks in order to determine whether effects of Zn deficiency on plasma and liver essential fatty acid composition could be distinguished from those of reduced protein and energy intake.

2. Fatty acid analysis revealed that a Zn intake of 3·4 mg/kg (plasma Zn 0·80 v. 1·97 mmol/l in controls fed on 36 mg Zn/kg) resulted in a significant increase in the linoleic acid: arachidonic acid ratio in both plasma and liver phospholipids in comparison with rats fed on 36 or 411 mg Zn/kg.

3. Zn supplementation (411 mg/kg) decreased the linoleic acid: arachidonic acid ratio in plasma phosphatidylserine compared with that of the controls.

4. The previously reported increase in arachidonic acid (mol %) in liver triacylglycerol of Zn-deficient rats was shown to be a function of a reduced liver triacylglycerol pool size; quantitatively, triacylglycerol content of arachidonic acid in the liver was not significantly affected by Zn intake.

1. For a period of 24 d, young rats received a diet containing 120 g casein/kg or the same basic diet supplemented with 1·93 g cysteine/kg.

2. The thyroxine (T4) turnover was decreased in rats receiving the cysteine-deficient diet compared with that of rats on the supplemented diet. Moreover, the extrathyroidal T4 pool and T4 disposal rate decreased.

3. Cysteine deprivation also decreased the peripheral metabolism of 3,5,3'-triiodothyronine (T3). The T3 distribution space, extrathyroidal pool of T3 and T3 disposal rate were diminished.

4. In vitro, deiodination of T4 in liver homogenate assayed with endogenous glutathione (GSH) demonstrated decreased T3 production rates in the case of cysteine deficiency. This difference was minimized by the addition of GSH in amounts sufficient to saturate the reaction kinetics. In the light of this finding, GSH is probably involved in the promotion of certain thyroidal problems induced by a cysteine-deficient diet.

1. Six sheep, three animals per diet, were prepared with rumen fistulas and fed on frozen grass or grass–maize pellets to give magnesium intakes of 1·79 and 2·23 g/d respectively. The mean apparent availabilities of Mg in sheep fed on frozen grass and grass–maize pellets were 0·31 and 0·36 respectively.

2. The rumen contents were fractionated by straining the digesta through linen cloth and then differentially centrifuged to give 20 000 g and 100 000 g supernatant fractions.

3. In all sheep, regardless of diet, at 4 and 16 h after a meal, 50 and 60% respectively of the total Mg in the rumen contents was found in strained rumen fluid while 30 and 38% respectively of the total Mg was found in the 100 000 g supernatant fraction.

4. The net absorption of Mg from the temporarily isolated and washed reticulo-rumen was studied using either 100 000 g supernatant fractions of rumen contents from sheep fed on one or other of the two diets, or inorganic buffers containing the same concentration of Mg and other macroelements.

5. The Mg was readily absorbed from the 100 000 g supernatant fraction placed in the rumen with the rate of absorption being 7·3 μmol/1 per min (505 mg/d) from the supernatant fraction obtained from sheep fed on frozen grass and 11.3 μmo/1 per min (781 mg/d) from the supernatant fraction from sheep fed on grass–maize pellets. In the same sheep, the previously described rates of Mg absorption from the 100 000 g supernatant fraction were similar to those obtained from the comparable inorganic buffers.

6. The effects of varying concentrations of potassium and sodium on the net absorption rate of Mg (as 24Mg) and on the one-way efflux of Mg (as 28Mg) from supernatant fractions or rumen fluid and inorganic buffers were investigated using the temporarily-isolated and washed rumen in three sheep. Although the net absorption rate of 24Mg from supernatant fractions or buffers containing similar K concentrations varied significantly between sheep, a similar percentage decrease in the absorption rates of both 24Mg and 28Mg was found for each sheep as the K concentration was increased.

7. One pair of sheep was fed on the frozen grass and the other pair was fed on the grass–maize pellets. Their daily intakes of K were then increased to 50 g/d for 14 d by intrarumen infusion of potassium chloride. In three of the four sheep the plasma Mg concentration fell within 12 h of the start of the KCl administration. In all sheep urinary excretion of Mg decreased and its faecal output increased. The increased intake of K had no effect on the distribution of Mg in the rumen contents.

8. Gel-filtration chromatography of the 100 000 g supernatant fractions, regardless of the diet, showed that over 90% of the Mg in the 100 000 g supernatant fractions was associated with a low-molecular-weight fraction of about 200 Da which corresponded to the elution volume of magnesium chloride in 0·1 M-sodium chloride.

9. It is concluded that any binding of Mg ions to small organic molecules in the 100 000 g supernatant fraction of rumen contents played no significant role in the restriction of Mg absorption from the reticula-rumen. The depressent effect of increased K concentration in rumen contents on the net absorption of Mg is via a reduction in the absorptive flux rather than by increased secretion of Mg into the rumen fluid.

1. Incubation of isolated rat hepatocytes with nicotinamide or nicotinic acid showed that while both vitamers were taken up from the incubation medium, neither was utilized to any significant extent as a precursor of the nicotinamide nucleotide coenzymes, NAD and NADP, and neither was capable of preventing the loss of nucleotides that occurs on incubating the cells.

2. Incubation of hepatocytes with tryptophan showed that de novo synthesis from tryptophan permitted replacement of the nucleotides lost during incubation; at high concentrations of tryptophan there was an increase above the initial intracellular concentration of NAD(P). Incubation of hepatocytes with tryptophan also resulted in the formation and release from the cells of a considerable amount of niacin, as well as the two principal metabolities of NAD(P), N1-methyl nicotinamide and methyl pyridone carboxamide.

3. It is suggested that, in the liver, preformed niacin is not utilized for nucleotide synthesis, and indeed the function of the liver appears to be synthesis of niacin from tryptophan, and its release for use by extrahepatic tissues that lack the pathway for de novo synthesis of nicotinamide nucleotides from tryptophan.

1. Birds (n 169) which varied in age, live weight, nutritional history, physiological state and genotype were slaughtered and analysed for total body water. Before slaughter, birds were injected with the water isotopes tritiated water (TOH) or deuterium oxide (D2O), or both, to determine TOH space or D2O space, or both, as estimates of total body water in vivo.

2. At the mean total body water of all birds determined by desiccation, of 1096·4 (SD 424·1) g, TOH space and D2O space overestimated total body water by 10·4 and 8·5 % respectively. The difference between the isotopes was significant (P < 0·05).

3. Based on recovery of isotope it was postulated that the main reason for the observed overestimation of total body water in vivo was incomplete recovery of isotope due to the vacuum sublimation technique. The mean recovery (%) of added isotope to whole blood after vacuum sublimation was 93·0 (SD 2·6) and 92·4 (SD 5·5) of the theoretical concentrations of TOH and D2O respectively.

4. Nevertheless, accurate prediction of total body water was obtained from regression equations which included live weight and isotope-dilution space. Values required logarithmic (base 10) transformation before derivation of linear and multiple linear regression equations, and the precision of prediction was determined by the residual standard deviation (RSD).

5. Total body water could be predicted with nearly equal accuracy from live weight or isotope-dilution space (RSD 0·025 and 0·020 respectively). Prediction of carcass protein was more accurate from live weight (RSD 0·033) than from TOH space (RSD 0·036), and inclusion of both variables resulted in only a marginal decrease in RSD to 0·031.

6. The prediction of carcass fat and energy was markedly improved by the inclusion of isotope-dilution space in conjunction with live weight compared with live weight alone.

7. The relations show the developmental nature of body composition of domestic fowl given diets adequate in nutrients. The prediction equations demonstrate the precision possible for studies in which estimates of body composition in poultry are required without slaughter.