1. Two experiments are reported in which sodium and calcium salts of volatile fatty acids (VFA) were given to lambs as additions to two basal dietsof hay andconcentrate. The two diets induced distinctly different types of rumen fermentation. A low-concentrate diet gave higher acetic and lower butyric acid proportions in the rumen contents than a high-concentrate diet. The two diets were given to lambs to provide equal intake of digestible organic matter. In one change-over experiment with twelve sheep the nitrogen retention was determined, and in a second experiment involving sixty-four lambs the efficiency of the VFA salt to promote body-weight gain was estimated. 2. The estimated metabolizable energy (ME) from the high-concentrate diet was utilized significantly more efficiently than that from the low-concentrate diet to promote positive nitrogen retention and to increase empty body-weight and carcass weight. These differences in final live weight were not significant owing to the greater content of the alimentary tract of lambs given the low-concentrate diet. 3. On both diets the lambs receiving the additions of VFA salts grew faster and produced significantly greater empty body and carcass weights than the lambs receiving only the basal diets. 4. For promoting carcass gain the energy derived from the VFA salts appeared to be utilized more efficiently than the calculated ME above maintenance of the two basal diets. 5. There were no significant differences between the efficiency of utilization of the energy from acetate, propionate and butyrate to promote carcass gains. There was, however, a tendency for the response to acetate to be greater on the high-concentrate diet than on the low-concentrate diet. 6. With a low level of feeding but with positive N balance, addition of acetate resulted in a greater N retention than that of propionate with both diets. 7. It is concluded that if the reported low utilization of the ME of diets high in roughage is related to the proportion of acetic acid in the rumen contents, then the implied losses of energy may be associated with the formation of acetic acid rather than its utilization.

1. The effect, on the concentration of volatile fatty acids (VFA) in the rumen, of increasing the frequency of feeding from twice daily to four or six times daily was investigated in sheep given isocaloric rations containing VFA salts. In a second experiment isocaloric rations containing acetate and propionate were given to groups of lambs in two or six equal feeds daily. The efficiency with which the lambs utilized the VFA salts was measured as gain in live weight, empty body weight and carcass weight and was compared to that of lambs receiving only the basal ration. The composition of the carcasses was estimated from that of the loin. 2. Increasing the frequency of feeding from twice daily to four or six times daily significantly reduced the marked changes in rumen VFA composition associated with giving rations containing VFA salts twice daily. In lambs receiving acetate and propionate, final live weight, empty body weight and carcass weight were significantly greater than in lambs receiving only the basal ration (P < 0.001). The combustible energy from added VFA was apparently utilized more efficiently than the calculated metabolizable energy of the basal rations given above maintenance level, and there was no difference between the utilization of acetate and propionate. 3. There were no differences approaching significance between feeding twice daily and six times daily either between groups of lambs receiving only the basal diet or between those given the diets supplemented with VFA salts. Nor were there any interactions between VFA and frequency of feeding. 4. It is postulated that in ruminants the effect of frequency of feeding depends on the environment and level of feeding.

1. Beef fat (2.5%) and anchovy oil (2.5%; 2.5% plus 0.02% ethoxyquin; 5%) were incorporated into isocaloric cereal-based diets A, B, C and D and given to turkeys from 2 to 10 weeks of age. Diets A, B, and C contained 13 and diet D 26 i.u. α-tocopheryl acetate/kg. The lipids of diets B and D, which contained fish oil without ethoxyquin, autoxidized in the feeding troughs, but not seriously in the brief period of exposure permitted. 2. The birds all remained healthy and grew well, the only nutritional effects of the fish oil being a depressed storage of vitamin A in the liver at both levels of feeding (prevented by ethoxyquin) and a slightly adverse effect, at the higher level only, on food conversion ratio. 3. The skin fats of the birds given fish oil contained seven major and two minor fatty acids, derived from the fish oil, which were not present in the skin of the control group given beef fat, as well as one major fish oil acid present in much greater concentration in the birds given fish oil than in the controls. All these acids were present in the skin fats at about half or two-thirds of their concentrations in the dietary lipid, except for acid 22:5, which reached two or three times this level. 4. The stabilities towards autoxidation of the skin fats decreased in the order A > C > B > D, as their content of polyunsaturated fatty acids increased, but the greater stability of group C as compared with B was probably due, in the main, to the higher tocopherol content of the skin fat of the birds on the ethoxyquin-containing diet. Fishy flavours which developed on cooking showed a similar relationship to diet.

1. The results of over 500 determinations of the heat of combustion of the urine produced by cattle and sheep have been analysed statistically. 2. The analytical errors for nitrogen, carbon and heat of combustion were ±0.54, ±1.4 and ±2.2%. The error attached to an estimate of the heat of combustion of the urine produced by an individual sheep in 4 days was ± 10%.3. At the maintenance level of feeding, the heat of combustion of the urine (U kcal/ 100 kcal food) was related to the crude protein content of the diet (P%)by the equation

U = 0.25P+1.6

with a residual standard deviation of ±0.88 kcal/100 kcal.4. Regression analysis of the relation between the heat of combustion of urine and its N content showed significant differences with diet. The heat of combustion of the urine of sheep was 9.7 kcal/g C and of cattle 10.3 kcal/g C, and did not vary with diet. 5. It is shown that the variation in the heat of combustion of urine/g N and its relative constancy/g C arises largely from variation, from diet to diet, in the proportion of the N excreted as hippurate. 6. The results have been combined with the results of a similar analysis (Blaxter & Clapperton, 1965) of methane production by sheep to show that the ratio of metabolizable energy to digested energy varies very little from mean values of 0.82 for roughages, 0.85 for cereals and 0.79 for oilseed cakes and meals.

1. Body water content was estimated in sixteen pigs at each of three weights 27, 55 and 90 kg with tritium, 4-aminoantipyrene (4-AA) and N-acetyl-4-aminoantipyrene (NAAP). The values obtained were compared with chemical analysis of the whole carcass. 2. The tritium method estimated total body water content accurately at 27 kg live weight but overestimated it by approximately 10% at both 55 and 90 kg live weight. 3. Antipyrene was eliminated from the pig at a rate of 55%/h and could not be used for body water estimations. 4. Measurements with NAAP on nine pigs tended slightly to underestimate total body water content. Estimates with 4-AA showed no association with the values obtained by chemical analysis.

1. A series of trials has been conducted to investigate interactions between amino acids in the diet of the growing chick. 2. Diets were prepared in which the level of arginine was limiting. To these diets were added excess levels of lysine, histidine, isoleucine and leucine. Of these amino acids lysine was most effective in reducing the growth rate. Growth rate was restored by adding arginine. 3. The addition of excess quantities of lysine to a diet in which the level of tryptophan was limiting and the level of arginine adequate did not reduce growth rate. 4. These results confirm the existence of a specific interaction between arginine and lysine. The concept is discussed that such specific interactions between pairs or among small groups of amino acids might underly many of the phenomenons of amino acid imbalance.

1. Rats were given a rachitogenic diet with or without vitamin D for 1, 2, 3 or 4 weeks, and vitamin D was administered to a group of rats which had been deprived of vitamin D for 3 weeks. 2. Changes in enzyme activities of some tissues were followed histochemically. In general, changes in parathyroid preceded those in gut and kidney. Leucine aminopeptidase activity rose in the parathyroid, kidney and jejunum of the vitamin D-deficient rat as did the ribonucleic acid content of the parathyroid and the dehydrogenase activity of the gut. In contrast, the phosphatase activity of the gut and kidney fell in the vitamin D-deficient rat. All these changes were reversed during the 1-week recovery period. 3. A slower response of bones to both vitamin D deprivation and vitamin D dosage after deprivation was indicated by the changes in the percentages of ash in the bones and the changes in number and distribution of osteoclasts.

1. Coprophagy in rats was prevented by the use of a leather jacket and large-mesh, screen floor cages. 2. This caused considerable depression of growth of prevented rats compared with non-prevented rats on the same diet.

1. The dietary intakes of forty-one mothers were investigated during lactation, between the 6th and 20th weeks after delivery. The group comprised thirty primiparae and eleven multiparae. 2. The women studied were apparently lactating satisfactorily, as the infants were judged healthy and their average weekly weight gain was 193 g (6.9 OZ). 3. The average daily intakes of nutrients by the mothers were compared to those listed in Dietary Allowances for Australia. Intakes of calories, protein, calcium, iron and ascorbic acid were 514±75 (16%), 17.0±2.7 g(17%), 725±75 mg(36%), 5.2±0.43 mg (31%) and 21±5.3 mg (21%) respectively below the allowances for these nutrients. It is suggested that the allowances for calories, protein, calcium, iron and ascorbic acid may have been set at too high a level. 4. The incidence of successful breast-feeding in western countries compared with others is briefly discussed. It is concluded that diet plays a minor part and that the dominant factors are cultural and social.

1. In Expt 1 balance studies were carried out with six wether sheep receiving chopped hay and concentrates and given, 0, 5, or 101. water/day by intraruminal infusion. Allocation to two 3 x 3 latin squares was arranged to allow calculation of main treatment and residual effects.

2. Infusing 101.water/day increased the total daily urinary output of magnesium, phosphorus and sodium by 31, 45 and 100% (P<0.05). Faecal losses of Mg, and P tended to decrease correspondingly and with both elements retention remained positive but retention of Na became negative (P < 0.05). 3. Residual effects were not detected, and infusing 5 1. water/ day generally produced intermediate and non-significant effects. 4. When pellets made from dried, ground, young spring pasture or ccncentrates rich in Mg were included in the diet of four wethers in Expts 2 and 3, infusions of 101. water/day produced much greater decrcases in faecal losses and retentions of Na and K and greater increases in the urinary excretion of those elements than those found in Expt I. Effects on Mg, P and Ca balance were similar to those in the main experiment. 5. The biological significance of these results and relationships between the observed effects and the aetiology of hypomagnesaemic tetany are discussed.

1. Rhode Island Red and Light Sussex poultry attained their full size in about 6 months.

2. When they were held back by undernutrition so that they weighed only about 170g at 6 months of age and were then given unlimited food, they grew—like the normal birds—for about 6 months, i.e. till they were 1 year old, but still they did not attain the same stature as normal birds. 3. The pullets more nearly attained the size of their controls than did the cockerels. 4. On rehabilitation after the period of undernutrition poultry frequently suffered leg weakness which in its extreme form could be diagnosed as perosis. 5. Rehabilitated pullets began to lay large eggs after a comparatively short period of growth and when they were still a small size.

1. After feeding radioactive markers 85Sr and 45Ca for 10 days to weanling and adult rats receiving basal diets all of which contained adequate calcium and phosphorus to support normal growth, the skeletal retention of the markers was compared with that in litter-mates receiving seven different P compounds as dietary supplements so that the P intake was increased 2 to 3½ times. 2. In weanling rats a dietary supplement of KH2PO4 decreased the skeletal retention of 85Sr by some 30% without affecting the retention of 46Ca. In adults on this supplement, the skeletal retention of 85Sr was reduced by over 40% compared with controls on the same basal diet. 3. When the supplement contained Ca as well as P the reduction in skeletal retention of 85Sr in young and adult rats was greater than when no Ca was present in the supplement. 4. It is concluded that there was no experimental evidence to show that supplements of P which also contained Ca induced any Ca deficiency in the rats. 5. In rats receiving P supplements which also contained Ca, the ratio of the skeletal retention of 85Sr, experimental to controls, was 0.45 for weanling rats and 0.52 in adults, 34 weeks old. These ratios were not significantly different for any of the seven supplements used. 6. From comparisons with previous experiments, it is concluded that supplementation with Ca plus P is more promising as a remedial measure for decreasing the uptake of radioactive Sr from the diet than supplementation with Ca alone.

1. Sixteen experiments were made with eight sheep to determine the effects of various compounds on methane production, digestion and metabolism. 2. Two experiments with two sheep given stearic acid incorporated in the diet showed that it depressed CH4 production by 2.7 moles/mole stearic acid. The digestion of the basal diet was also depressed, the apparent digestibility of dietary cellulose falling from 61.7 to 55.0%. 3. Three experiments with two sheep given liquid paraffin (mainly the C18 hydrocarbon) by infusion into the rumen showed that it had no effect on CH4 production and that it increased the excretion of fatty acids in the faeces and the non-lipid energy of the faeces. 4. Oleyl alcohol infused into the rumen of one sheep had no effect on CH4 production. It was excreted unchanged in large amounts in the faeces and increased the faecal excretion of fatty acids. 5. A preparation of sulphated C18 and Cla alcohols infused into the rumen of one sheep reduced CH4 production by 11.4 moles/mole sulphated alcohol. The preparation also caused a large increase in the excretion of non-lipid calories in the faeces and in the heat production of the animal. A larger amount of sulphated alcohols, given by infusion into the rumen of another sheep, reduced CH4 production to 41% of the initial values in 5 days, but caused refusal of food. 6. Two experiments were made with two sheep in which lauric acid was given by infusion into the rumen: Food refusals occurred within 48 h of commencing the infusion. 7. Sodium lauryl sulphate given to two sheep by infusion into the rumen reduced CHI production by 8.4 moles/mole. It greatly increased the faecal loss of non-lipid energy and also increased the heat production of the animals. When two further sheep were given sodium lauryl sylphate incorporated in the diet, cellulose digestion was depressed. Evidence of hydrolysis of the sodium lauryl sulphate was obtained. 8. Lauryl alcohol had no effect on the CH4 production of one sheep, but increased the faecal excretion of lipid. Inorganic sulphate had no effect on metabolism in an experiment with a further sheep. 9. The results, together with previous work with oleic, linoleic and linolenic acid (Czerkawski, Rlaxter & Wainman, 1966a), suggest that depression of CH4 production is a function of molecules with both polar and non-polar activities, that is with surface-active properties, and that such compounds when given to ruminants have a greater affect on the CH4-producing organisms than on organisms concerned in cellulose digestion.

1. Rats were chronically depleted of protein by being kept on a 6% casein diet for 5–8 weeks. Control rats were fed on a normal diet. Both groups were injected intraperitoneally with L-[U-14C]lysine. Some rats from each group were then put on a protein-free diet to produce acute depletion. The animals were killed 3 days after the injection. 2. The organs and tissues were analysed for total nitrogen and radioactivity. Free lysine, total amino N and specific activity of free lysine were measured in muscle, liver and serum. The total muscle mass of the animals was determined. Samples of muscle and skin were fractionated and the sp. ac. of the fractions was measured. 3. The main loss of N in acute depletion was found in the viscera and carcass residue; the percentage of total body N contributed by muscle was increased in protein-depleted rats. 4. The depleted rats retained relatively more radioactivity in the internal organs and less in the carcass than normal rats. 5. The ratio of the sp. ac. in protein-bound lysine to the sp. ac. of free lysine showed that protein synthesis was reduced in the muscle of the protein-depleted rats, although there was no decrease in the amount or sp. ac. of free lysine even in severe depletion. 6. Sarcoplasmic and fibrillar proteins of muscle were equally affected by protein depletion, but there was some indication of a preferential decrease in protein synthesis in one of the skin fractions. 7. The results for muscle protein are compared with those given in the literature for liver proteins. It is suggested that the rat adapts to a low-protein intake by an alteration in the pattern of protein synthesis.

1. The action of raw and heated soya beans on pancreatic function was studied by measuring the amylase activity of the pancreases and intestinal contents of intact chickens and of chickens with ileostomies at fasting and after eating, before and after adaptation to heated and raw soya-bean diets, with a methionine supplement and without. 2. The concentration of amylase in the pancreases of 8-week-old chickens eating raw soya-bean diets was lower than that of those eating heated soya-bean diets. These chickens were deficient in methionine; supplementation of the raw soya-bean diet with methionine greatly increased the levels of amylase in the pancreases of such chickens; supplementation of the heated soya-bean diet with methionine increased the levels of amylase in pancreases to a smaller extent. 3. Methionine was less effective in increasing the amylase levels of the pancreases of 11-week-old chickens eating raw soya-bean diets, since at this age the deficiency of methionine was much less pronounced. 4. More amylase activity was found in intestinal contents of chickens eating raw soya-bean diets than in those eating heated soya-bean diets. 5. In vitro studies showed that fractions prepared from raw soya beans, all containing high levels of trypsin inhibitors, stabilized amylase activity despite the active proteolysis of other protein substrates in the same amylase-containing mixtures. 6. CaCl2 stabilized amylase activity in vitro in unactivated and activated pancreatic juice as such, and after additions of raw soya beans or their fractions before and after autoclaving. 7. The increased levels of amylase found in the intestinal contents of the chickens eating raw soya beans may represent greater secretion of amylase activity by the pancreas, stabilization of amylase activity by the raw soya bean, or both factors. Interpretation of measurements of amylase activity in the intestinal contents of chickens eating heated or raw soya beans is uncertain. 8. The bearing of this work on current views of the nutritional value of raw and heated soya beans is discussed.

1. A technique using a constant infusion of [ U-14C]acetate, [U-14C]propionate and [2–3-T]– hutyrate has been developed to measure simultaneously the production rates of acetic, propionic and hutyric acids in the rumen of sheep. 2. Infusions of 14C-lahelled acids suggested that interconversions of acetic acid or hutyric acid with propionic acid and vice versa were small in extent, hut the conversion of acetic acid into butyric acid accounted for between 40 and 50% of the butyric acid produced. The conversion of hutyric acid into acetic acid accounted for 6–13% of the acetic acid produced in the rumen. 3. The production rates and the concentrations of individual acids in the rumen were simply related. 4. The difference between measured production rate and the rates of conversion of one acid into the other two acids for acctic, propionic and butyric acids, were 85–91%, 91–100% and 53–73% of the measured production rates respectively.

1. An assessment of the Islanders' food consumption on Tristan da Cunha before the volcanic eruption of 1961 was made (Part 1). The mean daily intake of energy was 2030 kcal per person and the calories derived from protein, fat, carbohydrate and alcohol accounted for 21, 26, 50 and 3% respectively of the total calorie intake, the proportion of calories derived from protein being about twice that found in other types of diet. 2. The weekly food intake of thirty-seven families resident at Calshot, Hants, was measured in July 1963, 3–4 months before the Islanders left England to return to Tristan da Cunha (Part 2). The mean intake of energy was 1750 kcal per person per day and the calories derived from protein, fat and carbohydrate accounted for about 12, 41 and 47% respectively of total calorie intake, proportions similar to those found in present-day British diets. The proportion of other nutrients in relation to calories also resembled those in British diets, except for vitamin A and ascorbic acid, which were relatively low in the Tristan diet. 3. A comparison of the results for the Islanders with those for a sample of households surveyed for the National Food Survey was made. The Islanders consumed less of all nutrients, and the average energy value met only 65% of estimated requirements compared with 108% in the British sample. 4. Details of foods consumed and of the Islanders' food patterns and preferences are given. There is some evidence that the Tristanidns did not like their former staple foods, potatoes and fish, as available in England, though at the time of the survey they had not appreciably switched to the British staple, bread. 5. The relatively low food intake reported in this study conforms with that recorded in the Norwegian investigation of 1937–8 (Henriksen & Oeding, 1946) and with calculations of island food supplies before 1961 (Part 1). 6. Possible explanations for the low food intake are discussed. It is suggested that the Islanders may not be very active and that energy balance studies on individuals who have returned to Tristan da Cunha might throw some light on the results of this survey.