1. An experiment was carried out to study more precisely by nitrogen balance techniques the intake of digestible crude protein required for maintenance in the mature non-pregnant ewe. 2. Four isocaloric diets supplying adequate energy, approximately 90 kcal/kg W0.73 metabolizable energy daily, and differing in crude protein content were each given to eight individually penned ewes. The diets provided 2.4, 4.9, 7.7 and 9.5 g digestible N per ewe per day. 3. The average weight of the ewes was 57.4 kg. They were rationed according to metabolic body-weight (W0.73) at a rate of approximately 800 g dry matter per 50 kg ewe per day for a 4-week period before N balance studies were carried out over an 8-day collection period. 4. The mean apparent digestibilities of dry matter were 67.3±0.8, 68.1±0.7, 70.9±1.0 and 68.8±0.8 respectively. The apparent digestibilities of N, increasing with increasing N intake, were 30.6±2.1, 46.3±2.1, 58.2±0.6 and 61.5±1.3 respectively. 5. The intake of apparently digested N required for maintenance was calculated in three ways, from the regressions of apparently digested N on N retention or on urinary N and from the underlying relationship between N retention and urinary N. The estimates so obtained were respectively 0.185±0.037, 0.148±0.020 and 0.150±0.020 g N per kg W0.78 per day, corresponding to 1.16, 0.93 and 0.94 g apparently digestible crude protein per kg W0.73 per day. 6. Metabolic faecal N, determined by the extrapolation method, was 0.629±0.047 g/100 g dry matter consumed. 7. The results are discussed in relation to practical feeding standards and other research findings.

1. A machine is described which automatically releases previously weighed rations to individually penned sheep at hourly intervals for 24 h. 2. Six sheep were kept in a room with constant light, temperature and continuous background noise and given 912 g lucerne daily at 10.00 h or at hourly intervals by means of the automatic feeder. Faeces and urine were collected every 2 h. 3. Hourly feedings reduced the variation between 2-hourly collection periods by 47, 87, 90, 85, 70 and 91% for total dry-matter content of the faeces, faeces dry-matter concentration, total urine output, urine specific gravity, urine nitrogen concentration and total N content of the urine respectively.

1. The metabolism of seventeen steers was determined on forty-nine occasions during fasts of either 112 or 136 h duration.

2. Faeces continued to be produced during fasts of up to 136 h duration at rates which were 15–20% of those noted before the fasts began.

3. Carbon dioxide production and oxygen consumption fell continuously throughout with animals weighing less than 200 kg but changed little after 88 h in animals weighing more than 200 kg. Methane production was considerably reduced during fasting but did not disappear. Urinary nitrogen excretion changed very little. Of the total loss of energy from the body, the loss of protein accounted for 25%. This was unaffected by age or size of animal.

4. With individual Ayrshire steers, metabolism increased during growth with body-weight raised to the power 0.68±0.05. No greater precision of estimate was obtained from logarithmic regressions of metabolism on body-weight than from linear ones.

5. Seven Ayrshire steers had a mean fasting metabolism of 100±1.6 kcal/kg W0.73 24 h, eight Black cattle of the Aberdeen Angus type a fasting metabolism of 81±1.5 kcal/kg W0.73 24 h and two Ayrshire x Beef Shorthorn steers a fasting metabolism of 96±2.9 kcal/kg W0.73 24 h. Variation in the fasting metabolism of an individual steer from time to time, expressed as a coefficient of variation, was ±7.4%.

6. The results are discussed in relation to interspecies generalizations about the relation between fasting metabolism and body-weight.

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. Sheep fitted with rumen cannulas were fed at hourly intervals by an automatic feeder in a controlled environment and the contents of the reticulo-rumen were removed at intervals of 6 h, 30 min after the previous feed. 2. No diurnal variation was found in the total contents or in the quantity of dry matter, organic matter and nitrogen. 3. Nine dried pasture herbages containing 0.79–3.69% N in dry matter were given automatically at a high and a low level of feeding. Feeding at the high level increased the total weight of the reticulo-rumen contents, total dry matter, organic matter and N and also the dry-matter percentage. 4. Apparent retention times were calculated by dividing the quantity of organic matter or N in the rumen by the quantity given each hour. Organic matter was retained for 10.2–24.9 h and N for 12.0–61.4 h. 5. The apparent retention times for both organic matter and N were reduced when the level of feeding was raised.

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. Beef fat oxidized to a peroxide value of 109 μmoles/g (218 m-equiv./kg), with a reduction in iodine value of 3.4 units, was incorporated at a 5% level in the diet of day-old chicks (diet 2) and stored for 8 weeks at room temperature during feeding. Similar diets containing fresh fat (diet 1, peroxide value zero) or oxidized fat in which the peroxide had been largely destroyed by heating (diet 3, peroxide value 2 μmoles/g) were also used. The diets contained adequate but not excessive levels of all vitamins, including stabilized vitamin A, except that for half of the chicks the supplement of stabilized vitamin E was omitted. 2. No further oxidation of the dietary lipid occurred during storage, and the initially high peroxide value in diet 2 decreased rapidly. The natural vitamin E decreased by more than 50% in diet 2, but remained unaffected in diets 1 and 3. 3. The chicks grew normally, with no difference in weight gain or feed conversion between the groups, the only differences attributable to the diets being marginally lower vitamin A levels accumulated in the livers of the birds on diet 2 and ajustdetectablyhigher liver weight in the birds on diet 3. 4. One of the twelve chicks receiving oxidized fat (diet 2) without synthetic vitamin E developed encephalomalacia. There was no other suggestion of performance being inferior as a consequence of the absence of the vitamin E supplement. 5. No difference could be detected in the flavour of the chickens, either freshly roasted or reheated.

1. A test was carried out simultaneously in Shinfield, Reading, England, and Columbus, Ohio, USA, using typical British and American rations for growing pigs. The rations were compounded in their country of origin; half of each consignment was used at the home station and the other half shipped to the overseas station. 2. Both restricted feeding and ad lib. feeding methods were used at each station. 3. A similar pattern of results was obtained at Shinfield and Columbus. Pigs receiving the American ration, which was higher in energy content, grew faster and required less feed per kg live-weight gain than pigs receiving the British ration. The higher energy content of the ration was probably responsible also for the poorer carcass quality of the pigs receiving the American ration, particularly the high fat content. The comparison between restricted feeding and ad lib. feeding was not affected by the type of ration. Restricted feeding resulted in slower growth rate, slightly better efficiency of feed conversion and considerably better carcass quality.

1. Thirty wether sheep comprising five of each of the following breeds, Scottish Blackface, Welsh Mountain, Cheviot, Suffolk Down, Kent and Hampshire Down, were subjected to a standard series of experiments in which energy metabolism was measured during fasting and at the maintenance level of nutrition, and in which maximal voluntary intake of food was measured and the metabolic responses to the stress of wind (10 miles/h) and rain (1 cm/h) were determined. 2. The weight of an individual sheep at the maintenance level of feeding was 8.4% greater and when given feed ad lib. 22% greater than its weight when fasted. These increases largely reflected changes in the weight of gut contents. 3. When fasting metabolism was expressed per kg weight raised to the power 0.73, the small Welsh Mountain sheep had the lowest metabolism of 54.1 kcal/kg W0.73 and the Cheviot sheep the highest of 64.4 kcal/kg W0.73. Overall breed differences were statistically significant (0.05 > P > 0.01). Evidence collected in the experiments, however, suggests that fasting metabolism was more closely related to body-weight raised to the power 0.85. When this basis for breed comparison was used, differences in fasting metabolism between breed groups disappeared. 4. No differences between breed groups in the proportion of the energy they ingested which was lost in faeces, in urine or as methane, were found when they were given food at a maintenance level. The Welsh Mountain sheep, however, had the smallest heat production at the maintenance level when expressed as kcal/kg W0.73. 5. No differences between breed groups in the apparent digestibility of the energy of feed given ad lib. were found. The voluntary intake increased with weight of sheep. When the amount of feed energy consumed and the energy apparently digested were related to the determined maintenance requirement for apparently digested energy of each sheep, no differences between breed groups were found. The efficiency of feed utilization by these breed groups of sheep when given feed ad lib. was the same. 6. It was found that the Hampshire sheep were the most resistant to the effect of wind on their heat production, and the Welsh Mountain sheep the least. The Scottish Blackface was most resistant to the effect of rain on heat production. 7. It is concluded that metabolic differences between different breeds of sheep differing widely in size are quite small, but that breeds differ markedly in their resistance to environmental stresses caused by wind and rain, and that these largely reflect the characteristic fleece types of the breeds concerned.

1. Turkey poults were fed from day-old to 6 weeks on a practical-type diet containing 10 % white fish meal (supplying 0.7 % lipid) and other constituents, mainly cereals (supplying 3.3 % lipid), together with either 1.5 % of anchovy oil that had been allowed to autoxidize under various conditions or 1.5 % of fresh beef fat.

2. For group I the whole diet with anchovy oil was stored in air at 15° for 3 months before feeding. Its lipid oxidized only slowly, with no appreciable rise in peroxide value and little destruction of its polyunsaturated fatty acids. For groups 2 and 3 the anchovy oil was mixed with the white fish meal, and the mixture was stored for 3 months, by which time most of its polyunsaturated fatty acids had been destroyed by autoxidation and the pv of the extractable lipid, after reaching a peak of 260 μmoles/g, had fallen again to 110. At this point the anchovy oil-fish meal premixture was further mixed with the basal diet and used, either immediately (group 2) or after 3 months' further storage (group 3). 3. The turkeys in all three groups receiving ‘fish oil’ remained healthy and grew well, with only slightly apparent (and not significantly) lower weight gains than those on the control diet. There was no significant treatment effect on liver weight, serum aspartate amino-transferase or serum alanine aminotransferase activity. All the birds stored vitamin A in their livers, though the diets had provided not more than adequate supplies of this vitamin, but the reserves accumulated were significantly lower when the diets contained oxidized fat. On roasting, the turkeys of group 1 had a definite and objectionable fishy flavour, whereas those of groups 2 and 3 were as palatable as the controls on the beef fat diet.

1. A study has been made of the protein requirements for maintenance and for growth of children about 1 year old who had recovered from malnutrition. 2. The diets used supplied 120kcal/kg daily; the sole source of protein was dried skim milk. 3. The average maintenance requirement, measured by nitrogen balance, was found to be 100 mg N/kg day. At this level of intake the net protein utilization (NPU) of cow's milk protein approached 100. 4. An intake of 200 mg N/kg day was enough to produce normal growth and N retention. 5. The amount of N retained was 2.9 g/100 g weight gain, indicating that no excess of fat was being laid down. 6. These results are in close agreement with theoretical studies of the protein requirement of children at this age.

1. The relationship of vitamin A and carotenoids with encephalomalacia was examined in chick-raising farms and under laboratory conditions. 2. In encephalomalacic chicks on the farms a significant decrease in liver carotenoid content was demonstrated. In the diseased chicks the carotenoid contentwas below 0.30 mg/100 g liver, as against the normal values of 0.40–1.0 mg/ 100 g. 3. Under experimental conditions incidence of encephalomalacia could be decreased by oral treatment with the synthetic carotenoid ethyl β-apo-8'-carotenoate. This implies that deficiency in carotenoid is not merely a concomitant sign of encephalomalacia, but has also a causative role, as sufficient carotenoid reserves confer a certain protection against the disease. 4. The pathogenetic role of carotenoid metabolism in encephalomalacia was supported by certain observations. Factors inhibiting the accumulation of ethyl β-apo-8'-carotenoate in the liver predispose chicks to the disease. In chicks 4–5 weeks old in addition to those with vitamin A reserves higher than 800 i.u./g liver, the accumulation of carotenoids in the liver was about 10% of that measured in chicks more than 7 weeks old, or in those with vitamin A reserves not higher than from 100 to 200 i.u./g. In fact, encephalomalacia occurs mainly among chicks 3–5 weeks old. Also, reserves of vitamin A exceeding 800 i.u./g liver were found to predispose chickens to encephalomalacia.

1. A total of sixty-three wether lambs, 4–6 months old, were fed on diets low in phosphorus and adequate in calcium (0.072–0.073% P, 0.38–0.40% Ca) or adequate in both (0.38–0.40% P, 0.40% Ca) for 134 or 142 days. 2. Concentrations of serum inorganic P and Ca and alkaline phosphatase activity were studied during the depletion period. Bones were taken for histological analysis at the end of the 142 days. 3. After the preliminary depletion period, a metabolism study was conducted in which the effects of previous P depletion and dietary Ca:P ratio upon Ca and P absorption, as measured by isotope techniques, were studied. 4. Histological analysis of bones showed the presence of lesions characteristic of late rickets in some sheep and of severe osteoporosis in others. 5. A wide dietary Ca:P ratio had no apparent effect on P absorption when P intake was adequate. The availability of P was lowered by a diet deficient in P with a wide Ca:P ratio. 6. Previous P depletion resulted in enhanced P absorption during the first 11.5 days after an increased intake of P, but this effect was not shown during days 14–21 after the increase. 7. Ca absorption was reduced by giving a diet low in P and was increased when the intake of P was raised. 8. The response to wide dietary Ca:P ratios by ruminants and non-ruminants is reviewed, and a hypothesis, based upon a knowledge of the intestinal reaction of these species, is offered for the finding that ruminants tolerate wider dietary Ca:P ratios than non-ruminant species.

1. An experiment was conducted in which sodium and calcium salts of acetic, propionic and butyric acids were given to groups of eight lambs as additions to basal diets of hay and concentrate. Two control groups were included, one group which received only the basal ration and one high-level control group which received sufficient additional concentrate to achieve growth rates greater than those of the groups receiving volatile fatty acid (VFA) salts. 2. With rumen-fistulated sheep, the effect on the rumen VFA composition and the pH of the rumen liquor, of diets supplemented with VFA salts given twice daily, was also investigated and compared with the effect of the basal diet alone. 3. The lambs receiving the VFA salts grew faster and achieved significantly greater empty body and carcass weights than those receiving only the basal rations; the high-level control group had significantly greater empty body and carcass weights than groups receiving salts of VFA. 4. There were no differences approaching significance in the efficiency of the three VFA in promoting gains in live weight, empty body weight and carcass weight. There appeared to be equal efficiency of utilization of the gross energy of the VFA and of the calculatedmetabolizable energy of the concentrates. 5. The effect of twice-daily feeding on the rumen VFA composition was that the concentration of the supple- mentary acid was greatest shortly after feeding, and about 5–6 h after feeding the effect was difficult to detect. There were no differences in the pH of the rumen liquor between animals given diets containing VFA salts and those given the basal ration.

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. A comparative study was undertaken with rats on the effect of various diets (normal stock, fat-free, palm oil and olive oil) on the in vitro incorporation of [14C]acetate by the liver into cholesterol and into the fatty acids of phospholipids and neutral fats. 2. The total lipids extracted from the incubation mixtures were fractionated into acetone-precipitable and digi- tonin-precipitable portions and also into the fatty acids of neutral lipids. 3. The incorporation of [14C]acetate into the acetone-precipitable fraction and into fatty acids of neutral fats was greatest in livers of rats given the fat-free diet, followed by those of the groups given olive oil, the normal stock diet, and palm oil. Livers from the group given the fat-free diet also exhibited the highest percentage of 14C activity in the digitonin-precipitable fraction and were closely followed by the group on the normal stock diet. Compared with those of the other two groups, the livers of the groups given olive oil and palm oil showed much less activity in the digitonin- precipitable fraction. 4. The greater the amount of a specific type of fatty acid in the diet, the less was the 14C activity incorporated into that type of fattyacid in the ncutral fats of liver slices, hut this was not so with the fatty acids obtained froin the acetone-precipitahlc fraction of the lipids.

1. In two experiments with growing and fattening lambs sodium and calcium salts of volatile fatty acids (VFA) were added to a basal diet of hay and concentrate. In Expt I the lambs were approaching maturity, and the utilization of salts of acetic, propionic and butyric acids was studied. In Expt 2 the animals were younger; the experimental groups received acetate or propionate, and half of them were implanted with hexoestrol. The chemical composition of the carcass was assessed with the loin as a representative joint. The influence of the VFA salts on the digestibility of the basal ration was also investigated. 2. In both experiments the lambs receiving supplements of VFA salts grew faster, and their empty body weights and carcass weights were significantly greater than in lambs receiving the basal diet. 3. The energy derived from acetate and propionate was utilized more efficiently to promote carcass gains than the calculated metabolizable energy above maintenance of the basal ration. There were no differences in the utilization of energy from the different VFA, except in Expt I in which butyrate was utilized somewhat less efficiently than acetate and propionate. 4. Hexoes-trol implantation resulted in faster growth, and highly significantly greater empty body weights and carcass weights. There was no evidence of an interaction between the VFA and hexoestrol treatments. 5. There were no differences between the VFA treatments in the composition of the carcass gains as judged by the composition of the loins, except in Expt I in which lambs receiving acetate tended to be the fattest. The coefficient of variation in loin fat percentages was large in both experiments, but, in Expt I in which both ewe and wether lambs were used, the coefficient of variation among the wether lambs was four times that of the ewe lambs. 6. Additions of VFA salts to the diet resulted in a significant increase in the excretion of ash.

1. Injections of 32P and 45Ca were used to study the influence of phosphorus depletion and repletion on the rates of endogenous calcium and P excretion in fifteen P-depleted and eighteen control sheep. 2. When given adequate P, there was a marked increase in the rate of excretion of metabolic faecal P in sheep which previously had been depleted. In control sheep a decrease was found in metabolic faecal P excretion with a diet deficient in P. 3. From the values for metabolic faecal P an indirect estimate of total intestinal secretion was made. The estimate was found to be in approximate agreement with values derived from published values for total daily digestive secretions in sheep. 4. The estimated rates of secretion of intestinal P suggest that after the addition of P to the diet the changes in the rate of excretion of metabolic faecal P in P-depleted sheep were the result of a decreased reabsorption of intestinally secreted P rather than of a change in the rate of secretion into the intestine. After a diet low in this element the decrease in metabolic faecal P excretion by control sheep appeared to be the result of a decreased rate of intestinal P secretion. 5. The possible significance of changes in metabolic faecal P excretion in relation to body P homoeostasis in the ruminant animal is discussed.