1. The kidneys of normal rats were analysed for water, fat, protein, RNA and DNA, at 10, 21 and 36 d after birth. The effects on growth caused by two types of malnutrition were investigated.

2. An increase in the RNA:DNA ratio was demonstrated between 10 and 36 d, contrary to previous evidence that this ratio is fixed at birth.

3. Energy deficiency during the first 21 d of life resulted mainly in fewer kidney cells, whereas protein-energy deficiency between 21 and 36 d resulted mainly in a smaller cellular content of RNA and protein.

4. In response to metabolic acidosis, both groups of malnourished rats increased urinary excretion of ammonia and there was enhanced gluconeogenesis in vitro; the basal rate of gluconeogenesis was lower in the protein-energy-deficient rats than in the controls.

5. Protein-energy-deficient rats did not exhibit the renal hypertrophy shown by the control rats in response to acidosis.

1. The rate of flow of digesta along the intestinal tract, and particularly the changes occurring in proteins during their passage through the intestine were determined in six rams; each animal was fistulated with three cannulas which involved six different sites of the intestine. Cr2O3 was used as a marker substance to measure the rate of flow of the digesta.

2. In the sections of the intestine from 1 to 15 m posterior to the pylorus the amounts of water, dry matter and total nitrogen decreased gradually as a result of their absorption through the intestinal wall. The region of the intestine situated at a distance of 7–15 m from the pylorus was more active with respect to the absorption of N, whereas water and dry matter were adsorbed to a greater extent in the region from 1 to 7 m from the pylorus.

3. The only part of the intestine in which substantial increases of water, dry matter and total N were found was the section immediately distal to the pylorus, and these increases were caused by the inflow of bile, and pancreatic and duodenal juices. The net increase found beyond the entry of the common bile duct was 2.7 g protein N and 2.0 g non-protein N (NPN)/24 h.

4. The activities of trypsin, chymotrypsin and carboxypeptidase A and the ratio α-NH2 NPN: protein N increased from the pylorus up to a distance of 7 m and decreased again from this point to a distance of 15 m from the pylorus.

5. In the sections of the intestine between 1 and 3 and between 3 and 7 m distant from the pylorus the extent of proteolysis exceeded considerably that of absorption of amino acids through the intestinal wall. This was concluded from the decrease in the rate of flow of protein amino acids (by 31% between 1 and 3 m distant from the pylorus and by 34% between 3 and 7 m) and the simultaneous increase in non-protein amino acids (by 20% in the region between 1 and 3 m) or no change in non-protein amino acids (between 3 and 7 m).

6. The relatively greater decrease in non-protein amino acids (by 57%) compared with that of protein amino acids (by 41%) occurring in the section 7 to 15 m distant from the pylorus showed that this is an area of most intensive absorption of amino acids.

7. In the lower section of the intestine, from 15 to 25 m distant from the pylorus, the total amount of amino acids showed almost no change; probably a net effect of loss and gain of amino acids mainly due to microbial activities. Increases in the dehydrogenase activity suggested enhancement of bacterial activity in this lower region of the intestine.

8. The supply of essential amino acids to the tissues of sheep is improved, compared with the amino acid composition of the diet, as the result of ruminal biosynthesis of essential amino acids and ruminal degradation of non-essential amino acids and preferential absorption of essential amino acids through the intestinal wall, particularly in the section of most intensive absorption, 7–15 m distant from the pylorus.

1. Test diets were given to chicks from 1 to 28 d of age. The basal diet contained soyabean meal as the sole source of protein and contained no vitamin B12.

2. The basal diet supported poorer growth and feed conversion efficiency than did the same diet supplemented with 0.01, 0.03 or 0.3 mg cyanocobalamin/kg.

3. Each of the four diets was also offered with a supplement of 20 g propionic acid/kg. This caused a significant growth depression at all but the highest level of cyanocobalamin addition.

4. Methylmalonic acid was detected in the excreta of chicks that received the supplements of 0 and 0.01 mg cyanocobalamin/kg diet, and in those of chicks receiving 0.03 mg only for the chicks that were also receiving propionic acid.

5. The results suggest that giving the odd-carbon, propionic acid to chicks may increase their requirement for vitamin B12.

1. Protein concentrates were prepared from freshly cut lucerne by the Pirie process and freeze-dried. When supplemented with methionine or cystine and given to rats as the sole source of protein at 120 g protein/kg diet, the adjusted mean protein efficiency ratio was 2.89 (casein standard at 2.50). As a supplement to protein from barley meal the lucerne leaf-protein concentrate (LPC) was similar to casein.

2. To investigate nutritional safety, lucerne LPC supplemented with methionine was given to rats at high levels for 6 months; exposure of these rats to diffuse daylight was avoided to prevent a severe disfiguring photosensitivity reaction. At a dietary protein concentration of 100 g/kg, rats grew equally well with lucerne LPC or casein. When the supplement was given at protein concentrations of 200 or 300 g/kg the rates of body-weight gain of male and female rats were less than those of control rats given casein. However, after 5 months on the diets, body-weights of male rats had nearly reached those of the controls.

3. Apparent protein digestibility ratio was about 0.80 with all three levels of lucerne LPC.

4. Reproduction was normal in seventeen of the eighteen female rats given the lucerne LPC at the three levels; lactation was also normal and litters were successfully raised to weaning.

5. Organ weights, liver histology and blood haemoglobin were normal in male rats given the lucerne LPC for 6 months.

6. Total body lipid of male rats given lucerne LPC was about half that of the control rats given casein. Body protein was slightly increased, and moisture content was higher in rats given lucerne LPC.

7. The ‘whey’ remaining after precipitation of the protein from lucerne juice strongly inhibited the initial growth of mice given a complete control diet. The mice soon accommodated to the depressive effect of ‘whey’, and body-weight gains were normal during the 3rd week.

1. The photosensitizing effect of leaf-protein concentrate (LPC) prepared from lucerne (Medicago sativa) was demonstrated when it was included in the diet of albino rats at concentrations between 40 and 480 g/kg diet.

2. Skin lesions of varying severity up to the sloughing of ears and tails occurred when such rats were illuminated with natural daylight through window-glass or with simulated daylight from a bank of lamps having emission maxima at 410, 437 and 660 nm and with approximately 4% of the energy of summer sunlight.

3. Protein concentrates prepared from ryegrass (Lolium multiforum) and a crude chlorophyll extract of spinach (Spinacea oleracea) did not cause these effects.

4. Extracts from blood plasma and livers of rats given lucerne LPC contained pheophorbide-a and two other unidentified green pigments, but no detectable phylloerythrin or chlorophyll. Extracts from the blood of rats given ryegrass LPC had no detectable pheophorbide or other chlorophyll-derived pigments.

5. The lucerne LPC given to the rats contained relatively large amounts of pheophorbide-a among a variety of pigments. The ryegrass LPC and the spinach extracts had only small amounts of this pigment relative to the other chlorophyll-type pigments.

6. These findings indicate that pheophorbide-a and related pigments are the agents responsible for the photosensitization of the rats. Possible explanations of their presence in lucerne LPC are discussed.

1. Weanling rats were given diets containing all the nutrients known to be required, with L-amino acids in place of protein. Dietary supplements were added isonitrogenously.

2. Torula yeast (50 g/kg diet) and dried brewers' yeast (50 g/kg) significantly improved the rats' growth rate. Part of this activity was attributed to the minerals present in the yeasts, zinc, iodine, iron, copper and manganese all being implicated.

3. Marmite (20 g/kg) and a basic fraction (6.6 g/kg) obtained from it by cation-exchange chromatography significantly improved growth. The ash component of the basic fraction was inactive.

4. Growth was increased by an extra supplement of vitamins and by treating the rats with neomycin sulphate and tetracycline. The growth stimulus due to Marmite was additive with that due to the antibiotics, but not with that due to the vitamin supplement.

5. The growth rate with torula yeast (50 g/kg) was maintained at about 30% greater than on the basal diet during a test lasting 80 d. At the end of that period six control and five supplemented male rats sired normal litters. Post-mortem examination, including histology, of others showed no abnormalities due to factor G deficiency.

6. Fresh ox liver (100 g/kg diet) significantly improved the growth rate, but this improvement could be attributed to the effects of the water and minerals contained in the liver.

7. These results confirm the discovery by Schwarz, Smith & Oda (1966) that yeasts contain an organic growth-promoting factor (factor G) for rats receiving amino acid diets. Factor G is not likely to be one of the vitamin B group.

1. Chicks at 10 d of age were given diets containing all the nutrients known to be required, with L-amino acids in place of protein. Dietary supplements were added isonitrogenously.

2. Ox liver (100 g/kg) greatly improved the chicks' growth rate, whereas torula yeast (50 g/kg) was inactive. The activity of fresh moist liver was considered to be due largely to an organic factor, because of the inactivity of water and the low activity of liver ash.

3. The growth rates of chicks receiving diets based upon casein and isolated soya-bean protein were significantly improved by the inclusion of 100 g fresh ox liver/kg, but not of 50 g torula yeast/kg.

4. These results show that chicks receiving an amino acid diet require an organic growth factor (Progressin) that differs from the yeast factor required by rats receiving an amino acid diet.

1. The nutrient content of battery, deep litter and free range eggs from domestic hens under systems of management typical of those used in the commercial production of eggs was studied from January to March 1968.

2. Monthly samples of eighteen eggs, supplied by six centres, were homogenized, freezedried, ground and stored at −15°. Their contents of moisture, nitrogen, amino acids, fats, fatty acids and cholesterol, ash, sodium, potassium, calcium and iron, thiamin, riboflavin, nicotinic acid, pantothenic acid, folic acid, vitamin B12, tocopherols and retinol were determined. The mean values for eggs from each system, each centre and each quarter of the year were calculated.

3. For many nutrients, no significant difference between systems was detected; the greatest variations occurred in the content of some vitamins. Free range eggs contained more vitamin B12 than deep litter or battery eggs and more folic acid (Lactobacillus casei assay) than battery eggs. Differences in tocopherol and cholesterol contents were complicated by system-by-centre interactions. There were also small differences in calcium and iron contents.

4. Riboflavin, folic acid (Lactobacillus casei) and vitamin B12 were the only nutrients which were observed to vary with the time of year in the eggs from all systems of management. Major differences were found in the vitamin content of eggs from different centres.

5. Though the differences in vitamin B12 and folic acid contents which result from the different systems of management are of little significance in an average mixed diet, they would be measurable for some individuals who may depend on eggs as an important source of these nutrients.

1. Acetate, propionate, butyrate and glucose were each administered intravenously (2.09 MJ (0.5 Mcal)/d) to lambs on either high-concentrate (HC) or high-roughage (HR) diets in two experiments with 4 × 4 Latin square design. During a control period all animals received a saline infusion.

2. In lambs on the HC diet glucose was the most effective metabolite tested for improving nitrogen retention. Acetate was 51%, butyrate, 75%, propionate, 90% as effective as glucose in promoting N retention. Propionate infusion was most effective in increasing N retention in lambs on the HR diet. Acetate was 60%, butyrate, 75%, and glucose, 80% as effective as propionate. Glucose infusion did not lower plasma urea N (PUN) concentration in lambs receiving the HC diet, but the three volatile fatty acids (VFA) did lower it (P < 0.01). All energy sources significantly reduced the PUN concentrations with the HR diet, but differences between sources were not significant.

3. Plasma concentrations of valine, isoleucine, leucine and phenylalanine were depressed to 57, 71, 89 and 90% of their control values during glucose, propionate, butyrate and acetate infusion. Plasma concentrations of lysine and methionine were significantly decreased from control values (P < 0.05) but there was no significant difference between energy sources. Lysine, valine, isoleucine and leucine were significantly (P < 0.01) higher in lambs given the HR diet than in lambs given the HC diet. The concentration of alanine was greater (P < 0.05) during glucose infusion than during acetate and butyrate infusions, indicating net synthesis of alanine and possibly other non-essential amino acids during glucose infusion, since the plasma free amino acid N concentration increased despite decreased concentrations of plasma essential amino acids during glucose infusion.

4. The results indicated that glucose and propionate were superior to acetate and butyrate as energy sources for protein formation.

5. The poor relationship between PUN and N balance and plasma free essential amino acids suggested that PUN concentration may have been inappropriate to assess the protein status under some dietary conditions.

1. Protein digestibility of two proteins was measured when these proteins were given together and separately to rats.

2. The influence of carbohydrates on protein utilization (true protein digestibility, biological value and net protein utilization) was also studied. Autoclaved potato starch was replaced by increasing amounts of glucose, sucrose, fructose and lactose respectively. Glucose, fructose and sucrose appeared to have no specific influence on protein utilization when given in increasing amounts and when compared with autoclaved potato starch. Higher concentrations of lactose, however, caused diarrhoea.

3. The true digestibility of the protein components in a mixture was directly related to the true digestibility of each protein component, including proteins of low digestibility.

1. The effects of the protein content of the diet on the vitamin B12 concentration of serum and of various tissues were studied in rats by means of microbiological and radioisotopic techniques.

2. Protein starvation reduced tissue weights and nitrogen contents, serum protein concentrations and haemoglobin values.

3. The vitamin B12 contents of the serum and of several organs and tissues were greater in the protein-starved animals for reasons that remain unexplained.

4. The retention of radioactive cyanocobalamin per g fresh weight was significantly greater in liver, kidney, spleen and brain in the protein-depleted rats than in those given adequate protein. However, the total tissue retention was not significantly different between these groups, so that there was a greater capacity for tissue binding and for body conservation of vitamin B12 in the protein-starved animals.

1. Preruminant calves, some of which were equipped with re-entrant cannulas in the small intestine, were given liquid feeds in which various starches, maltose or lactose formed the sole source of carbohydrate.

2. The sugars left the abomasum at the same rate as a water-soluble marker but the starches were greatly delayed. Little starch left the abomasum until about 5 h after feeding. Examination of abomasal contents 0.5 h after feeding showed the starch to be associated with the casein clot.

3. Amounts of starch, maltose and lactose removed during the passage of digesta through the small intestine were about 60, 43 and 97% of intake respectively, with no marked difference with age between about 7 and 16 weeks.

4. No change in blood glucose was apparent in calves given starch-containing feeds. The possible effect of the retention of dietary starch in the abomasum in minimizing blood glucose responses is discussed.

1. Pigs from 20 to 47 kg live weight were given a wheat–safflower diet supplemented with either 0, 2 or 4 g L-lysine/kg either once daily or in six equal portions at intervals of 3 h.

2. The addition of lysine at both levels significantly (P < 0.001) increased growth rate, feed conversion and lean content of the ham.

3. Frequency of feeding had no effect on the response of pigs given the control diet.

4. A significant interaction (P < 0.05) between frequency of feeding and lysine supplementation occurred for growth rate. Growth responses to the supplements of 2 and 4 g L-lysine/ kg with once-daily feeding were only 43 and 69% of those achieved under the frequent-feeding regimen.

1. The folate and vitamin B12 in milk are strongly bound to minor whey proteins. These binder proteins are present in excess, and so milk has capacity – which varies between milks of different mammalian species – to sequester added cyanocobalamin and folic acid.

2. A study was made of the influence of different milks on uptake of [3H]cyanocobalamin and [3H]folic acid in selected bacteria, mostly of types that are commonly found in the intestine.

3. None of the test cultures required exogenous vitamin B12. Nevertheless, when free cyanocobalamin was added, in seven of nine cultures it was rapidly taken up into the cells, though there were large differences between the different bacterial species in their absorptive capacity. In presence of sow's milk, little or none of the added cyanocobalamin was taken up, even after incubation of the test mixture for 1 h at 37°. The avidity of sow's milk for cyanocobalamin, as judged from its retention of the vitamin against competition by bacterial cells, was greater than that of a preparation of porcine Intrinsic Factor of similar binding capacity.

4. Of ten cultures of bacteria representing seven species, only the five cultures that required exogenous folate took up added folic acid into the cells. Uptake was severely depressed by the simultaneous addition of goat's colostrum, even after incubation of the test mixture for 1 h at 37°.

5. The physiological role of the binders is discussed. It is postulated that they may act in the mammary gland as trapping mechanisms to accumulate the vitamins from blood plasma into milk and in the gut to facilitate their absorption, both directly, and indirectly by preventing their uptake by intestinal micro-organisms. It is concluded that the binders might well influence the vitamin economy in the neonatal period, and the ecology of the gut microflora.

1. The catabolism of valine was estimated in vivo by measurement of the production of labelled CO2 for 2 h after the oral administration of either [U-14C]valine or [I-14C] valine. It was also estimated in vitro in homogenates of liver and muscle incubated with labelled valine. Experiments were performed in rats given diets providing either 215 g (HP) or 25 g (LP) protein per kg diet.

2. The proportion of [U-14C]-valine excreted as 14CO2 was not reduced in rats given the LP diet for 16 d but the excretion of 14CO2 from [I-14C]valine was reduced by 40% in these animals. When rats were transferred from the HP diet to the LP diet there was a reduction in the excretion of 14CO2 from [I-14C]valine; when the diet was changed from LP to HP output of 14CO2 increased to control values.

3. Homogenates of muscle and liver catabolized valine to CO2. Both liver and muscle from rats fed on the LP diet catabolized less [I-14C]valine than tissues from control animals.

4. Valine aminotransferase activity was higher in muscle than in liver, and did not change in tissues from rats fed on the LP diet. In these animals 2-ketoisovaleric acid dehydrogenase activity was reduced in both liver and muscle.

5. The production of 14CO2 was lower with [U-14C]valine as the substrate than with [I-14C]valine and there was no difference between tissues from rats fed on the HP and LP diets.

6. The results with [I-14C]valine suggest that both liver and muscle from protein-depleted rats catabolize valine at a reduced rate. The reason for the discrepancy between these results and those with [U-14C]valine is not clear. It is concluded that the results with [U-14C]valine in vitro are affected by dilution of the label before the formation of 14CO2, but that this does not hold in vivo.

1. A machine is described which is small enough to fit into a respiration calorimeter and which enables sheep to be fed automatically up to twelve times daily.