1. A study has been made of the effect of feeding growing rats for a long time on a low-protein, high-carbohydrate diet given at two different levels of energy. 2. When the proteins of the diet provided o or 5% of the calories the body-weight fell rapidly and fat accumulated in the liver. Addition of carbohydrate (glucose) to the diets increased the amount of fat in the liver. 3. It is suggested that a deficiency of protein retards the synthesis in the liver of lipoproteins required for removal of triglyceride from the liver. Additional carbohydrate diverts amino acids from the amino acid pool to tissues such as muscles, increasing the liver damage.

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. Three sheep were given three diets, a control diet consisting mainly of cereals, a similar diet incorporating linseed oil (mainly glycerides of linolenic acid) and a diet incorporating free fatty acids derived from linseed oil. The diets were given at the maintenance level and at twice this level according to a latin square design. 2. Complete energy balance was obtained and the digestibilities of cellulose and lipid were determined with each sheep receiving each diet. The relative amounts of various fatty acids in the dietary and faecal lipids were also estimated. 3. The inclusion of lipids in the diet resulted in a significant decrease in cellulose digestion, whereas the lipid digestibility increased. 4. The proportion of C18 acids increased in the faeces, and the proportion of bacterial fatty acids decreased, but since the total amount of fatty acids excreted increased, the amount of bacterial fatty acids excreted per day did not differ significantly in animals receiving the control diet and the diets containing added lipids. 5. The addition of lipids to the diet resulted in a highly significant drop in methane production, the depression being about 25% of the control value. The depression (28.9 kcal/100 kcal of fatty acids given) was considerably greater than the depression produced by continuous infusion of the same amount of fatty acids. 6. Because of the depression of CH4 production and of some reduction in the urinary energy losses, the addition of lipids to the basal diet increased the metabolizable energy by about 9.5 kcal/100 g of the basal diet. 7. The efficiencies of utilization of metabolizable energy were not significantly affected by addition of lipids, being about 82% for maintenance and 62% for fattening. 8. In an experiment with one sheep, comparison was made between the effect of slow continous infusion of fatty acids over 24 h and the effect of rapid infusion of the same amount twice daily during feeding. The continuous infusion of linseed oil fatty acids resulted in a drop in CH4 production of 16.3 kcal/100 kcal of fatty acids given. This was in good agreement with previous findings. Rapid infusion of these fatty acids resulted in a drop in CH, production, amounting to 28.0 kcal/100 kcal of fatty acids infused. This is comparable with the reduction of 28.9 kcal/100 kcal fatty acids when the fatty acids were incorporated in the diet.

1. Fifty-six albino rats were distributed between four dietary groups in fourteen randomized blocks of four animals. Each block consisted of siblings and each member of the block received a different dietary treatment. 2. The diets permitted normal growth and the only variations were: group I contained 67% sucrose, group 2 an equivalent amount of uncooked maize starch and groups 3 and 467 % of finely ground Thin Wine and Morning Coffee biscuits respectively. 3. After 31 days on the diet, the animals were killed and assessed for dental caries. The rats of group I had significantly more caries than the other groups. The rats of group 2 had significantly less caries than the other groups. The biscuit diets produced significantly less caries than the sucrose diet, but significantly more caries than the starch diet.

1. The effect of reducing the hay and of increasing the proportions of concentrate and flaked maize in the diet of cows on the secretion of milk fat and its component fatty acids and on the proportions of volatile fatty acids in the rumen liquor has been studied. 2. The low-hay diet caused a fall in the milk fat content to about half of the values in the initial control period and the secretion of all the major fatty acids in the milk was reduced. The general pattern of change in the proportions of rumen VFA during the change to the low-hay diet was a decrease in acetic acid, an increase in propionic and n-valeric acids, relatively little change in n-butyric acid and also an increase in the concentration of lactic acid. Approximately 60% of the variation in milk fat content during the change of diet was associated with the increase in propionic acid. 3. In cows established on the low-hay diet there were marked variations in the relative proportions of acetic and propionic acids, but there was no related change in milk fat content. On return of the animals to the high-hay diet, recovery of the initial proportions of acetic, propionic and valeric acids occurred within about 4 days but the recovery in milk fat content was not complete until 2–3 weeks had elapsed. 4. Although the intraruminal infusion of acetic acid in cows on the low-hay diet caused increases and decreases respectively in the molar proportions of acetic and propionic acids in the rumen, an increase in milk fat content was observed amounting to only one-quarter of the loss associated with the transfer to the low-hay diet; therem was no characteristic pattern of increase in the yields of the individual fatty acids of milk fat. No consistent effects of intraruminal infusions of butyric acid, in cows on the low-hay diet, on the yield of milk fat or of the individual fatty acids were observed.

1. Thirty Ayrshire bull calves were used in an experiment to study the effects of diets containing different proportions of concentrates to hay on rumen development at 12 weeks of age. In addition, six milk-fed calves were slaughtered at 3 weeks of age for comparison. 2. Restriction of the maximum daily allowance of concentrates to the lower levels was accompanied by an increase in the voluntary intake of hay, but the performance of calves from 3 to 12 weeks of age was significantly better in calves given the high-concentrate diets. 3. The weight of contents of the reticulo-rumen increased from 0.7 kg at 3 weeks of age in the milk-fed calf to 7.7 kg and 10.9 kg at 12 weeks in calves given the high-concentrate and high-roughage diets respectively. Between 68 and 79% of the total contents of the alimentary tract was contained in the reticulo-rumen of the ruminant calf. The weight of contents of the omasum was significantly greater in calves given 1.36 kg concentrates/day than in those given either 0.45 or 2.27 kg concentrates/day. Equations were developed from the results by which the weight of contents of the various parts of the alimentary tract, and hence empty body weight in the live animal, can be determined from a knowledge of the live weight and daily consumption of concentrates and hay, 4. Volume displacement of the reticulo-rumen tended to increase with increase in the proportion of hay in the diet. The volume displacement of the omasum increased in response to concentrate intake up to a maximum of 1.36 kg/day and thereafter declined, but the nature of the diet had no significant effect on the volume displacement of the abomasum. 5. Calves given the high-concentrate diets had a significantly greater weight of reticulo-rumen tissue at 12 weeks than those given the high-roughage diets. 6. Whereas the thickness of the muscular wall of the rumen did not differ significantly between treatments, there was an increase in the length and density of papillas, particularly in the anterior dorsal and ventral sacs of the rumen, as the intake of concentrates was increased. The results show the marked relationship between the performance of the animal and an advanced stage of development of the rumen papillas.

1. The intake and excretion of energy, total nitrogen, fat and carbohydrate by twenty baby boys aged about a fortnight were measured over 3 days. 2. Ten of the babies received breast milk which had been expressed from their mothers, the remaining ten received one of two preparations based on dried cow's milk, with either lactose or sucrose added. 3. The intake of energy, protein and carbohydrate was greater in the ten babies receiving the cow's milk preparations. 4. The urinary excretion and retention of N was greater in the babies fed on the cow's milk preparations. 5. The absolute excretion of N in the faeces was simiIar whatever the diet, but the excretion of fat was less and the excretion of carbohydrate greater for babies having breast milk. 6. The calorie:N ratio in the urine was 5.8 kcal/g urinary N in those receiving breast milk and 4.8 kcal/g N in those fed on the cow's milk preparations. The value for the adult is 7.9. 7. Calorie conversion factors have been calculated which are more appropriate for milk diets for babies than the factors of Atwater which were designed for mixed diets for adults.

1. Diets containing cottonseed hulls and flaked infrared-toasted soya beans, cottonseed hulls and soya-bean meal or cottonseed hulls alone were fed to three fistulated steers. 2. The diet containing toasted soya-bean flakes was associated with the highest concentrations of total nitrogen, protein N, and ammonia N in the rumen liquor; the diet of cottonseed hulls was associated with the lowest concentrations; and soya-bean meal was associated with intermediate concentrations. 3. Concentrations of residual N were highest in rumen liquor during the first 3 h after feeding when soya-bean meal was given and highest with the other diets between 10 and 12 h after feeding; concentrations of non-protein N were highest with the toasted soya-bean flakes at all times except approximately 2 h after feeding when they were highest with soya-bean meal. 4. The rumen liquor was more acid with soya-bean flakes than with the other diets. 5. The total concentration of volatile fatty acids (m-moles/100 ml) was highest with the diet containing toasted soya-bean flakes, followed by that with soya-bean meal and cottonseed hulls and lowest with the cottonseed-hull diet. The molar percentage of acetic acid was highest with soya-bean meal, whereas its concentration (m-moles/100 ml) was highest with soya-bean flakes. Propionic acid concentrations were highest with the toasted soya-bean flakes. 6. These results indicate that the metabolism in the reticulo- rumen of infrared-toasted whole soya beans given as flakes differs from that of soya-bean meal.

1. Measurements were made of the proteases, amylase and lipase of the pancreas and of the corresponding intestinal, caecal and colonic contents of germ-free and conventional rats. 2. Little difference was found between the concentration of the enzymes in the germ-free and conventional rats. 3. The results indicate that intestinal bacteria had only a minor part in determining the fate of the pancreatic enzymes in the contents of the intestine, caecum and colon. 4. The enzyme concentrations decreased caudally. The proteases were the most stable, and the amylase was the least stable; the stability of lipase was intermediate between that of the proteases and amylase. 5. Evidence of bacterial activity in the caecal contents of conventional rats was seen in the greater percentage of protein nitrogen and in the lower percentage of the non-protein nitrogen

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. For 26 weeks, adult male rats were fed on diets containing about 80 % of carbohydrate, given as dextrose, fructose, liquid glucose, or sucrose; their performance was compared with that of rats receiving a standard laboratory cubed diet (41 B) containing 60 % of carbohydrate, mainly as starch. 2. More of diet 41 B was eaten than of any of the diets containing sugars, but only with dextrose was the mean body-weight gain significantly lower than with diet 41 B. 3. No significant differences in body length or girth were produced by the different diets. 4. Compared with those of rats given diet 41B, plasma cholesterol levels were significantly in- creased by fructose and sucrose and to a lesser extent by dextrose, but not by liquid glucose. 5. Compared with those given diet 41 B, the rats given fructose had heavier hearts, kidneys and livers, those given sucrose had heavier hearts and livers, and those given dextrose had heavier hearts. Those given fructose had the heaviest kidneys and livers, and heavier hearts than those given liquid glucose. The organ weights of those given liquid glucose and those given diet 41 B were not significantly different. 6. Compared with the values on diet 41B, carcass and liver fat were both significantly increased by sucrose and fructose but not by dex- trose or liquid glucose. With fructose, liver fat was almost double that with dextrose or liquid glucose. 7. Dry-matter contents of whole carcass and liver followed substantially the same pattern as did the fat contents. 8. Liver protein content was significantly lower on the 80 % carbohydrate diets. The reductions were greatest with fructose and sucrose.

1. The food and water intake and diurnal variations in the rumen contents were measured in sheep with rumen fistulas receiving semi-purified or pelleted roughage-concentrate diets. The rates of secretion and composition of parotid saliva of the sheep on both diets and of sheep fed on hay were determined. The sheep had continuous access to the diet. 2. The mean daily intakes of the semi-purified and roughage-concentrate diets were 920 and 2234 g respectively. The corresponding water intakes were 2.50 and 6.05 1.3. Noneof the sheep ruminated on either diet. The weight of total contents and of dry matter in the rumen was highest in animals on the roughage-concentrate diet, and marked diurnal fluctuations, which reflect the eating habits of these animals, were observed. The semi-purified diet appeared to have a very marked water-retaining capacity in the rumen. 4. The estimated daily total secretion of both parotid glands was 2.7, 5.4 and 11.5 1. in sheep fed on the semi-purified diet, roughage-concentrate and hay respectively. No appreciable differences were observed in the composition of parotid saliva between the three groups of sheep. In sheep receiving hay, saliva secretion was lower during eating than between periods of eating, during part of which time the sheep presumably ruminated. 5. It is concluded that the observed differences in parotid secretion reflected differences in the physical form of the diet.

1. Two experiments were conducted to examine the effect of grinding and pelleting roughages on the voluntary intake of food, digestibility, time of retention of food in the digestive tract, amounts of digesta in the recitulo-rumen and eating and ruminating behaviour of adult, non-lactating, non-pregnant cows. The first experiment was with artificially dried grass and the second with oat straw; also, with a diet of ground, pelleted oat straw the effect was studied of giving a daily intraruminal infusion of 150 g urea. The size of the particles of the ground roughages are given. 2. The mean voluntary intakes of long and ground dried grass were similar, the voluntary intake of ground, pelleted oat straw was 26% greater than that of long straw and the daily infusion of urea increased the voluntary intake of ground, pelleted oat straw by 53%. 3. The digestibility of the ground roughages was lower than that of the long roughages, the lower digestibility of the ground roughages was due mainly to the poor digestibility of crude fibre in the reticulo-rumen. The rate of disappearance of cotton thread placed in the ventral sac of the rumen was slower with ground than with long roughages. 4. The mean times of retention of ground roughages were shorter than those of long roughages when equal and restricted amounts of each food were given; with food offered ad lib. there was little difference between the mean times of retention of long and ground roughages in the alimentary tract. 5. On average, the mean amounts of digesta dry matter in the reticulo-rumen immediately after a meal were about the same with long and ground dried grass, with long and ground oat straw the amounts of dry matter were similar, but when the intraruminal infusion of urea was given the amount of dry matter increased by 49%. 6. The rate of eating (min/kg food) ground, pelleted roughages was much faster than that with long roughages; when the cows received ground roughage rumination did not occur but during short periods triple reticular contractions were seen. 7. The relationship between the voluntary intake of food, the amount of digesta in the reticulo-rumen and the rate of disappearance of digesta from the alimentary tract is discussed.

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. Loss of NH3 N from faeces and urine between voiding and collection and also losses in expired air, eructed gas and from the skin of wether sheep 2–3 years old given a ration of 400, 700, 1000 or 1300 g dried grass/day have been measured. 2. Losses of NH3 from faeces were negligible, and the loss from urine depended on the temperature and pH at which it was collected. Collection at neutral pH resulted in losses of up to 9.7% of the urinary N as NH3 gas if an acid trap were not incorporated in the collection apparatus. The average loss of N on collection of urine at pH values below 2.0 was 1.33% when the ambient temperature was between 25 and 28°, and 0.97% when it was between 15 and 18°. 3. Very little NH3 was lost in expired air or eructed gas, but when total NH3 loss other than that from urine was determined, an average loss of 3.14±0.55 mg N/kg body-weight per day was found. This loss was independent of food intake and larger than the loss of N in suint which was estimated to range from 0.59 to 2.55 mg N/kg body-weight per day with the rations given. It was concluded that the larger losses found in some experiments were due to splashing of urine on to the fleece during collection and subsequent loss of this urine N as NH3. It was shown that the losses of NH3 N due to errors in urine collection and failure to consider dermal losses ranged between 1.2 and 2.6% of the total determined losses in faeces and urine for sheep fed on a variety of diets and that the losses varied inversely with intake of N.

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. Lipids of the heart muscle, skeletal muscle and liver were investigated in healthy calves and in calves suffering from enzootic muscular dystrophy with special regard to the fatty acid composition of the phospholipids and triglycerides. 2. Healthy young calves and older calves differed in the fatty acid composition of these tissues. The tissue phospholipids of healthy young calves contained less linoleic acid and more monounsaturated fatty acids than those of older calves. Of the saturated fatty acids, palmitic acid content tended to be higher in young calves and stearic acid content tended to be higher in older calves. 3. The stearic acid content of tissue triglycerides was lower in young calves than in older calves. 4. Fatty aldehydes were present in the phospholipid fraction of the heart muscle and of the skeletal muscle. Stearaldehyde content was higher in older calves than in young calves. 5. In calves with muscular dystrophy definite changes in the fatty acid composition of the phospholipids were found. In young calves the content of linoleic acid was higher and that of monounsaturated fatty acids lower in tissues of diseased animals than in the corresponding tissues of healthy controls. Both in young and older calves arachidonic acid content was higher in the degenerated areas of the skeletal muscle than in the healthy controls. 6. Possible relationships between the tocopherol and arachidonic acid contents of the tissues are discussed. 7. In the triglyceride fraction the differences between diseased and healthy tissues were less significant than in the phospholipid fraction in young calves. In older calves no significant differences were found. 8. An increase in lipid content was found in the degenerated areas of the skeletal muscle and a decrease in livers from diseased animals. An increase in free cholesterol was found in the degenerated areas of the skeletal muscle. The triglyceride content of livers from diseased animals was decreased. The relative proportion of phospholipids was less in skeletal muscle and higher in liver of diseased animals than in the corresponding tissues of healthy controls.