1. Male rats of approximately 120 g body-weight were maintained on a commercial stock diet containing 204 g crude protein (nitrogen × 6.25)/kg, a hydroxyproline-free high-protein (HP) diet containing 200 g casein/kg as the only protein source, or a low-protein (LP) diet containing 40 g casein/kg. After 6 weeks on these diets half of each group was transferred to a non-protein (NP) diet and the experiment was continued for a further 6 weeks. Animals from each group were killed at 4 d, 3 weeks and 6 weeks after the transfer to the NP diet.

2. Throughout the experiment the urinary excretion of N, hydroxyproline and creatinine, and the content and solubility of the skin collagen were determined.

3. When compared with a control group killed at the beginning of the experiment the rats maintained on the LP diet showed an increase of 25% in total N content of the skin but collagen content increased by 100%. Rats transferred from the HP to the NP diet lost both N and collagen from the skin, but those transferred from the LP to the NP diet lost N but increased the collagen content by 42%.

4. Protein deprivation brought about marked changes in the solubility of the skin collagen, suggesting an increase in the rate of maturation of skin collagen.

The effect of oven-drying on the gross energy content of rat carcasses was investigated. No losses of carcass energy could be ascribed to oven-drying per se.

1. The effect of vitamin B12 on growth was studied in young male and female rats fed on diets sufficient (+B12) or deficient (−B12) in vitamin B12 containing 30% of the dietary energy as fat, either maize oil (CO) or triundecanoin (TUD).

2. Vitamin B12 deficiency severely depressed growth. After 6 weeks the weight gain of CO(−B12) rats was only 72% of that of CO(+B12) rats and the gain of TUD(−B12) rats was only 47% of TUD(+B12) rats.

3. After fasting 24 or 96 h TUD-fed rats, both + B12 and −B12, had greater glycogen reserves and higher plasma glucose levels than CO-fed rats.

4. It is concluded that vitamin B12 is required for the metabolism and utilization of both an odd-carbon-number medium-chain fat, TUD, and an even-C-number long-chain fat, CO, during growth in rats.

1. Within the limits of this study, neither maternal iron deficiency nor Fe-overload as measured at term appeared to affect the complement of Fe received by the foetus.

2. Infants feeding entirely on breast milk appeared to have normal Fe status 6 months postpartum regardless of the Fe status of the mother.

3. No relationship could be demonstrated between the Fe content of breast milk and the Fe status of the mother.

1. Semi-synthetic diets, with dried microbial cells (Pruteen) as the nitrogen source, were used to measure N retention in 50 kg pigs which had been given only sufficient N (5.3 g/d) to maintain N equilibrium for the previous 12 d. Control pigs were given 33.2 g N/d.

2. Metabolic faecal N losses were 1.62 g/d (1.2 g/kg dry matter eaten) and endogenous urinary losses were 3.90 g/d.

3. Realimentation of N-deprived pigs was achieved with diets providing 20.0, 33.2 and 67.4 g N/d and daily rates for N retention were 11.2, 17.8 and 25.9 g respectively; the corresponding value for control pigs was 15.0 g. ‘Catch-up’ protein growth was demonstrated in pigs given both 33.2 and 67.4 g N/d. In the former instance, this was associated with an increase in the efficiency of utilization of dietary N.

4. The biological value of the protein in Pruteen was 0.85, and it appeared that under conditions of increased demand for N the pig could utilize some of the nucleic acid-N fraction of this protein source.

1. Young chicks fed a diet deficient in calcium showed an eightfold increase in the in vitro renal production of 1,25-dihydroxycholecalciferol (1,25-DHCC) and those fed a diet deficient in phosphorus showed a threefold increase when compared to chicks on a normal diet.

2. The in vivo accumulation of 1,25-DHCC in the gut mucosa was doubled in both low-Ca and low-P groups as was the rate of Ca absorption from the duodenum and the Ca-binding protein activity. The accumulation of 1,25-DHCC in bone increased threefold in the low-Ca group but showed no change in the low-P group.

3. It was concluded that the increased rate of Ca absorption found in dietary P deficiency depends rather upon the capacity of the gut mucosa to accumulate larger amounts of 1,25-DHCC than upon an increased renal production of this metabolite. The mechanism by which this is achieved is unknown, but it unlikely to be a general increase in availability of 1,25-DHCC since no rise occurred in bone 1,25-DHCC levels.

1. Male and female rats aged 3 weeks were divided into two groups. One group of each sex was allowed unlimited access to the stock diet, the other group was given the stock diet in restricted amounts for 10 weeks so that the males gained only 19 g and the females 21 g in comparison with 176 g and 116 g for the well-nourished males and females respectively. The undernourished animals were then rehabilitated by being allowed the stock diet ad lib.

2. Five animals of each sex were killed at various stages of the experiment, their bodies analysed for fat and nitrogen, and the size and number of fat cells determined in specific fat depots.

3. The undernourished rats failed to make a complete recovery and were significantly smaller than the controls of the same sex at 172 d of age when the experiment terminated.

4. The previously undernourished rats deposited significantly more fat in their bodies during rehabilitation than the control animals in the same number of days and over the same gain in body-weight.

5. There were no significant differences in the number of cells containing fat at the abdominal fat site between the undernourished and rehabilitated animals and the controls at any stage, nor were there any significant differences in apparent fat cell numbers between the control and rehabilitated animals at any of the other sites studied when the experiment ended at 172 d.

1. The distribution of radioactive iron in 59Fe-labelled rat muscle extract was determined using ge filtration. This showed that most (approximately 70%) of the radioactivity was associated with the heamatin compounds; myoglobin and haemoglobin.

2. Raw beef and freeze-dried rat muscle were digested in vitro, under simulated physiological conditions, and after centrifugation the supernatants fractionated by gel filtration. The soluble products were haematin Fe complexes of molecular weight above 10 000 and non-haematin Fe compounds of molecular weight below 6000, the major products being the non-haematin Fe complexes. The soluble compounds were also separated by dialysis and, in rat muscle, it was found that the low-molecular-weight non-haematin compounds accounted for more than 80% of the total soluble iron.

3. In vivo absorption studies with rats showed the Fe in a digested muscle dialysate to be more readily absorbed than that from an aqueous muscle extract which itself was more readily absorbed than the Fe from whole blood.

4. It may not, therefore, be the haemoproteins per se which are responsible for the high availability of Fe in meat, but rather the nature of their degradation products, formed by digestion within the meat environment.

1. A combination of a mineral balance and a radioactive technique has been used to study the effect of the dietary calcium intake of ewes in pregnancy on their Ca and phosphorus metabolism in lactation.

2. Ewes which had received a Ca-deficient diet in pregnancy absorbed Ca at a greater rate and with a greater efficiency in early lactation than did the control animals, which had received an adequate Ca intake in pregnancy. The apparent absorption of P was also higher in the Ca-deficient sheep.

3. Since both groups of sheep received the same high Ca intake in lactation, the increased rate of absorption of Ca must have resulted from an increased rate of active transport rather than an increased rate of diffusion.

4. Retention of both Ca and P was positive in the Ca-deficient ewes but negative in the control ewes. This difference in retention reflected a difference in bone metabolism.

5. The maximum rate of absorption possible, which is equal to the rate of irreversible loss of Ca from the rapidly exchangeable pool, was much greater in the Ca-deficient lactating ewes than was previously found in Ca-deficient wethers. This difference is due to the additional pathway of loss of Ca in the milk of the lactating animals.

6. The relationship between these findings and the prevention of milk fever in dairy cows by manipulation of the dietary Ca intake is discussed.

1. Concentrations of copper, manganese, zinc, nickel, cadmium and lead were measured in samples of liver, kidney, brain, heart, lung, skeletal muscle and vertebral bone from forty foetuses of 22–43 weeks gestation.

2. Cu concentrations in the liver were up to 100 times those in other tissues, but only those in the brain showed a significant increase with gestational age.

3. Mn concentrations were similar in all tissues; the over-all range was 0.35–9.27 μg/g dry matter (dm).

4. Concentrations of Zn in the liver were much higher than in other tissues and decreased with gestational age, whereas levels in skeletal muscle increased.

5. In all tissues Ni concentrations were within the range 0.04–2.8 μg/g dm and levels in kidney and muscle decreased significantly with age.

6. Cd was detected in most of the tissue samples and concentrations were within the range 0.01–0.58μg/g dm.

7. Concentrations of Pb, where it was detected, varied from 0.1 to 2.4 μg/g dm in the soft tissues and from 0.4 to 4.3 μg/g dm in the bone samples.

1. The objective of this study was to determine whether the chemical and biochemical changes induced by muscle wasting caused by dietary protein restriction are different in various skeletal muscles.

2. Rats were fasted for 3 d and then fed on a 10 g protein/kg diet for 21 d. Thirteen muscles from the trunk, forelimb, and hind-limb regions were analysed for muscle weight, and the content of water, fat, cellular and extracellular protein, DNA and RNA. Results were compared to values for an ‘initial’ control group killed at the start of the experiment.

3. Weight loss was greatest in trunk muscles and least in the distal forelimb muscles. Water content decreased in most muscles, but increased in three forelimb muscles. A significant loss of lipid was found in the gastrocnemius, while the biceps brachii gained lipid. Changes in lipid content of the muscles did not form a distinctive pattern.

4. All muscles except the distal forelimb muscles lost a significant amount of cellular protein, while all muscles except the diaphragm gained extracellular protein.

5. DNA content was unchanged in all muscles. The value for cellular protein:DNA was significantly reduced in the rectus abdominis and the diaphragm. A significant loss of RNA was found in all muscles; the percentage change was greatest in trunk muscles and least in the distal forelimb muscles. The values for RNA:protein and RNA:DNA were significantly lower in all muscles except two distal forelimb muscles.

6. With the exception of the water and lipid content of the muscles, the directions of the changes in the experimental animals were the same for all muscles. The results suggested, however, that the magnitude of changes in certain chemical and biochemical indices of composition may depend to some extent on the anatomical location of the muscle: trunk muscles tended to show the greatest percentage change, while the distal forelimbs changed the least.

1. Five sheep were given a meal while they were in a neutral environmental temperature (15–20°) and while acutely exposed to a moderately cold (1°, wind speed 2 m/s) environment.

2. Before and at various times after feeding measurements were made of hepatic portal blood flow and the concentration of volatile fatty acids (VFA) and glucose in arterial, hepatic portal and hepatic venous blood plasma. From these measurements the net rate of release of VFA from the viscera was calculated, and the uptake of propionate and output of glucose by the liver was estimated, assuming hepatic arterial blood flow to be 20% of portal flow. The concentration of insulin in arterial and portal venous plasma was also measured.

3. The change in environmental temperature did not affect the time taken by the animals to eat the meal completely.

4. After feeding, in the neutral environment, there were significant increases in portal blood flow and release of VFA into the portal bloodstream. The uptake of propionate by the liver increased, significantly, and output of glucose also increased, but not significantly. Plasma insulin concentration also increased after feeding.

5. During cold exposure portal blood flow was consistently higher, before and after feeding, than it was in the neutral environment. The release of VFA into the portal blood was also consistently greater during cold exposure, especially the release of propionate after feeding. Associated with this was an extra uptake of propionate and output of glucose by the liver. Plasma insulin concentration was slightly higher in the cold environment than the neutral environment before the animals were fed, but this difference was not apparent at any other time.

1. Sheep given constant feed were exposed to environments in which the oxygen concentration in air was either 200 or 150 ml/l. There were no differences in daily heat production, methane production, urinary energy or faecal energy losses measured over periods of 4 d.

2. When the sheep were fasted there were no differences in heat production to be ascribed to the O2 concentration in air. The thermic response to feed was unaffected by the O2 concentration in the air.

1. The syndrome induced by depriving cats of animal lipid is partially cured by feeding 18:3ω6. This is associated with an increase in levels of 20:3ω6, but not 20:4ω6, in plasma phospholipids.

2. It is concluded that the cat lacks Δ5 desaturase activity and has a dietary requirement for 18:3ω6 and possibly 20:4ω6.

1. Iron absorption from ferrous citrate (monoferrous acid citrate, FeC6H6O7H2O) was studied in normal healthy male and female volunteers using ferrous citrate labelled with radioactive Fe and whole-body counting. Ferrous citrate was either given alone or with a rice-based meal.

2. Fe absorption from ferrous citrate was satisfactory and was comparable to that from ferrous sulphate.

3. Fortification of crude cooking salt with ferrous citrate was not satisfactory due to colour development on storage. Ferrous citrate can, however, serve as an effective Fe fortificant with sugar or wheat flour.