1. The reproducibility of an assay for methionine based on live-weight gains in young chicks has been tested in a collaborative study in six laboratories.

2. Results were analysed by the slope-ratio procedure and, in general, the assays were statistically valid. The variability between laboratories was similar to that found in previous studies of variablity within a single assay in one laboratory.

3. With the combined estimates from five or six laboratories the standard error of the estimates was apporoximately 10% of the mean. Expressing response as‘g gain/g food eaten’ gave no more precision than using ‘weight gain’ alone, but is nevertheless thought to be less open to error due to apetite effects.

4. The experiments have shown that materials can be ranked consistently, but that the absolute estimates of potency varied between assays and further improvements are desirable if potency estimates are to be used for the calibration of in vitro procedures of protein evaluation.

1. The colorimetric micro-adaption of the iodometric method and the colorimetric thiocyanate method for the determination of lipoperoxides were compared. Similar results were obtained when methyl linoleate hydroperoxide was tested, but when lipid from rat liver, muscle, kindney and testes was examined, substantial amounts were found by the iodometric, but almost nothing by the thiocyanate method.

2. The main reason for the discrepancy between the methods seems to be that the iodometric micromethod also estimates substances other than true lipoperoxides. The presence of ubiquinone and vitamin A in the organ extracts was shown to interfere in this way in the method.

3. The yellow colour which develops when retinol and its esters are tested by the iodometric micromethod is due not to liberated iodine but to conversion products of retinol.

4. It is concluded that the occurrence of substantial amounts of lipoperoxides in vivo has so far been demonstarted only in the adipose tissue, and not in the parenchymatous organs of the rat.

1. Six experiments were undertaken with mature, dry, non-pregnant cows to determine the capacity to lose and recover nitrogen and to study the significance of the labile and total protein reserves.

2. It was concluded that, without altering its ability to reach N equilibrium, the mature cow is able to store and lose large amounts of body proteins (certainly more than 15 kg), when its N and energy intakes are greatly varied. The repletion or depletion of protein reserves can occur over a long period of time (sometimes more than 5 months). Total protein reserves include a very labile part. This part is more rapidly lost during fasting than during feeding on low-protein diets; it can be used to meet temporarily the energy requirements of the animal.

3. N balance and body-weight gains were generally very well correlated.

1. In two experiments, sheep prepared with a rumen cannula and with re-entrant cannulas in the duodenum and ileum were continuously fed on diets of dried grass, dried grass plus formalin-treated casein, or dried grass plus untreated casein. Paper impregnated with chromic oxide was given once daily via the rumen fistula.

2. In ten 24 h collections of digesta entering the duodenum and eleven 24 h collections of digesta reaching the ileum of sheep given dried grass, there were highly significant correlations between the 24 h flows of Cr marker and the corresponding flows of dry matter, organic matter, nitrogen, gross energy, hemicellulose and cellulose (P < 0.01) at both sites.

3. Daily amounts of non-ammonia N and of individual amino acids entering and leaving the small intestine and of total N excreted in faeces and urine are given.

4. Net retention of supplementary N was 36% when the supplement was administered as formalin-treated casein, but only 17% when it was administered as untreated casein.

5. Formalin treatment of casein significantly increased the daily amounts of non-ammonia N entering the small intestine (P < 0.01) and the amounts of non-ammonia N apparently absorbed therein (P < 0.05).

6. Apparent absorption of amino acids from the small intestine was significantly greater (P < 0.05) with treated casein than with untreated casein. There were relative increases in the small amounts of several free amino acids measured, including taurine, in the ileal digesta of sheep receiving the treated casein supplement.

1. Sheep prepared with a rumen cannula and with re-entrant cannulas at the proximal duodenum and terminal ileum were given diets of dried grass, and dried grass supplemented with formalin-treated or untreated casein. They were fed either continuously or once daily. Paper impregnated with chromic oxide was given once daily via the rumen fistula.

2. The observed daily flows of magnesium at the duodenum and ileum were highly correlated with the corresponding flows of Cr.

3. There was a net absorption of Mg from the stomach as well as the intestinal region of all sheep.

4. Protein supplementation had no effect on the extent or sites of Mg absorption, but altering the feeding regimen changed the proportions of the net absorption of Mg occurring in the stomach and intestinal regions.

1. Wild rabbits were caught during both phases of the excretory cycle and their gut contents were analysed for volatile fatty acids (VFA).

2. All rabbits were found to have high concentrations of VFA in the caecum and in the proximal colon. Acetic was the most abundant acid followed by n-butyric, then propionic.

3. VFA concentrations in the caecum and in the proximal colon of rabbits caught during the day and during the night were similar. Hard pellets from the distal colon and rectum of rabbits caught during the night had considerably less VFA than did the soft pellets from rabbits caught during the day.

4. Owing to the ingestion of soft faeces, the VFA content of stomach material was greater in rabbits caught during the day than in those caught at night.

5. The results are discussed in terms of the mechanism of the diurnal excretion pattern and the role of coprophagy in the rabbit.

1. The oxygen utilization of ten women was measured after consuming meals supplying 230–1200 kcal (0.96–5.02 MJ) in three experiments.

2. In the first experiment four subjects consumed one-ninth, one-third or one-half of the daily allowance and the oxygen consumption was measured for 3 h after the meal. The response was unrelated to the size of the meal.

3. Resting conditions were rigidly controlled in the second experiment. Each woman reclined on a bed for 5–7 h while the effect of a meal providing 600 or 900 kcal (2.51 or 3.77 MJ) for the two lighter subjects and 800 or 1200 kcal (3.35 or 5.02 MJ) for two heavier subjects was measured. A greater increment in energy expenditure was obtained after the larger meal for each subject. The effect of two 30 min walks before and after the large meal was negligible.

4. In a third experiment the effect of exercise was measured with five women consuming 900 kcal (3.77 MJ) (a) followed by 5 h rest and (b) preceded and followed by exercise (two 30 min walks on a treadmill). The energy increment during 90 min after the meal was equivalent in (a) to 15 kcal (63 kJ) per h and in (b) to 16 kcal (67 kJ) per h, whereas the response following exercise but without food was insignificant.

1. A study was made of the changes in electrolyte concentrations and ruminal function which resulted from the provision of 1.3% sodium chloride solutions instead of fresh water to sheep consuming roughage rations in chaffed and in ground pelleted forms.

2. Significantly higher osmotic pressures were observed in the rumen fluid of the sheep drinking saline water, the change being especially marked when the ration was ground and pelleted.

3. Of the individual electrolytes measured, chloride showed a larger rise in concentration than did sodium plus potassium and it appeared that the sodium and chloride ions in the ingested saline water were differentially removed from the rumen.

4. Provision of 1.3% NaCl solution in place of fresh water resulted in greater voluntary intakes of fluid and consequently in greater flows of fluid through the rumen.

5. Based upon measurements of deoxyribonucleic acid and polysaccharide, there appeared to be a tendency for the total microbial populations in the rumens of sheep drinking 1.3% NaCl solution to be smaller than for the sheep drinking fresh water.

6. The total metabolic activity of the rumen flora, measured calorimetrically, was not appreciably changed when saline water was drunk and the chaffed ration eaten, but was significantly reduced when the ration was ground and pelleted.

7. Adaptation of the rumen microflora to high concentrations of NaCl was demonstrated in animals accustomed to drinking 1.3% NaCl solution.

1. Groups of twelve female rats were fed from 4 weeks of age on four different experimental dietary regimens, and on a stock diet containing 18% protein given ad lib. as a control (group 1). The rats in two of the experimental groups were malnourished either by being given a low-protein (9%) diet ad lib. (group 2), or the stock diet containing 18% protein in limited amounts to maintain weight as in group 2. These animals were designated calorie-deficient (group 3). Two other groups of twelve rats were more severely malnourished from 4 to 13 weeks of age by being given a low-protein (6%) diet ad lib. (group 4) or the stock diet in limited amounts to maintain weight as in group 4 (group 5). From 13 weeks all the rats in groups 4 and 5 were rehabilitated on stock diet ad lib.

2. Well-nourished males were introduced into the cages 1 week after the vaginas opened, and again immediately after the females had suckled successive litters. This was repeated until the females were 60 weeks old and had reared up to six litters.

3. Chronic deprivation of protein or of calories delayed puberty, reduced fertility and gave rise to smaller numbers in the litters. It also interfered with lactation.

4. More severe malnutrition for 9 weeks further delayed puberty, but when these animals were rehabilitated they produced as many young as those that had been well-nourished throughout. They lactated well and there was no carry-over of the effects of the early deficiencies.

1. A comparative study on the digestibility of beef, buffalo, camel and mutton fats was made with chicks during the 4th week of age. Each fat was added to a low-fat diet at levels of 3, 6 and 9%.

2. The mean digestibilities of beef, buffalo, camel and mutton fats were 85.4, 72.6, 83.9 and 94.1% respectively. Thus mutton fat appeared to be significantly superior to other fats, whereas buffalo fat was significantly inferior.

3. The melting points of the fats seemed to have no influence on their digestibilities.

4. With the exception of beef fat, the digestibility of the fats improved as the iodine value increased.

1. Maltase sucrase, palatinase (the enzyme that hydrolyses palatinose, i.e. 6-o-α-D-gluco-pyranosyl-D-fructose) and lactase activities were measured in the small and large intestines of germ-free and conventional chicks given either a diet of purified ingredients or a practical chick mash.

2. With the purified diet there were no differences in body-weight or small intestinal disaccharidase activities between germ-free and conventional chicks. With the chick mash the germ-free birds were heavier and had higher total amounts of maltase, sucrase and palatinase activities in the small intestine than did their conventional controls. When disaccharidase activities were expressed in terms of body-weight there were no differences between birds in the two environments. Enzyme activities were consistently higher in the birds given chick mash.

3. Inclusion of milled fibre in the purified diet did not increase the weight or disaccharidase activities of the small intestine in either environment.

4. Lactase was virtually absent from the small intestine of birds in both environments and from the large intestine of germ-free birds. There was appreciable lactase activity in the large intestinal contents of conventional chicks, and it was increased by inclusion of lactose in the diet.

5. When lactose was the sole source of carbohydrate the birds grew poorly but mortality rate was less among conventional compared with germ-free chicks.

6. It was concluded that the presence of micro-organisms has no direct effect on disaccharidase production in the small intestine of the chick. Microbial lactase is present in the large intestine, and at least some of the products of its action can be utilized by the bird.

1. Standard zinc solutions for the atomic absorption analysis of rat plasma were prepared to contain 14% (w/v) of sucrose. In this way the problems of sample nebulization were overcome with a minimum of manipulation before assay.

2. Plasma Zn concentrations in rats were found to fall by approximately 40% (from 1.2 to 0.7 μg/ml) after 1 d on a Zn-deficient (< 0.25 ppm) diet. Thereafter, the fall became less marked and after 5 d the concentrations usually varied between 0.4 and 0.6 μg/ml.

3. A single oral dose (20–200 μg) of Zn was reflected in high plasma Zn concentrations in the depleted rats 1.75 h after dosing, but to a much lesser extent in animals receiving 10–60 ppm Zn in their diet before dosing.

4. It is suggested that the plasma Zn response to a single oral dose of zinc sulphate may provide a useful method for the detection of a subnormal Zn status in individual farm animals without the necessity of determining breed norms.

1. The effect of zinc deficiency on the activities of rat duodenal alkaline phosphatase and inorganic pyrophosphatase has been investigated.

2. Zn deficiency adversely affected the activity of these enzymes before growth rate and food intake were reduced.

3. The level of food intake was without effect on the activity of alkaline phosphatase but markedly influenced that of inorganic pyrophosphatase.

4. The relevance of changes in the activities of Zn-dependent intestinal enzymes to the food intake of Zn-deficient rats is discussed.

Experiments with a small-scale artificial rumen have shown that of forty-two compounds tested the majority were fermented, as judged by the production of volatile fatty acids, but methane production was associated only with the fermentation of formate, certain hydroxy-acids, pyruvic acid, primary alcohols (methanol, ethanol, propanol and butanol), glycerol and methyl compounds. With primary alcohols there was a stoichiometric relationship between methane production and the oxidation of the alcohols to the corresponding acids.

The fermentation of rhamnose and 1,2-propanediol was studied in detail. With both compounds there was a temporary accumulation of lactic acid and a continuous net production of propionic acid. The initial rate of acetate production was rapid with rhamnose but decreased subsequently, whereas propionate continued to increase. With propanediol the net rate of production of acetate was slow at first and then increased. There was no increase in the production of butyric acid with either rhamnose or propanediol, and the endogenous methane production was inhibited by 20–40%. There was evidence for the formation of an unidentified compound during fermentation of rhamnose and propanediol.

1. The production and metabolism of volatile fatty acids were studied in sheep offered a cobalt-deficient diet.

2. The molar proportions of acetic (60%), propionic (26%) and butyric (14%) acids in the rumen fluids of sheep given the Co-deficient diet, but whose stores of vitamin B12 were adequate, were similar before and after administration of an oral supplement of Co.

3. In pair-fed sheep, one member of which was vitamin B12-deficient and the other (control) treated with vitamin B12 parenterally, the concentrations after feeding of both total and individual volatile fatty acids in the blood tended to be higher in deficient than in control sheep.

4. Following injection of the respective salts of individual volatile fatty acids into the blood-stream, formate clearance was apparently not affected, whereas that of acetate was slightly, and that of propionate very significantly, delayed in vitamin B12-deficient sheep compared with pair-fed control animals.

5. Acetate metabolism was retarded in the presence of propionate; the effect was greater in deficient than in pair-fed control sheep.

6. The hypothesis is advanced that it is the failure to metabolize propionate at the normal rate that leads to the progressive loss of appetite in vitamin B12-deficient sheep.

1. The absorption rates of L-methionine and L-methionyl-L-methionine (dimethionine) from the upper jejunum and lower ileum of the rat were studied in vivo after different dietary treatments. Rates were expressed per unit gut length and per unit gut weight; the former was considered to be the more satisfactory under the different dietary conditions.

2. The dietary treatments were either short-term (10 d) or long-term (40–84 d).

3. The rate of absorption of methionine increased in the jejunum after a restricted dietary intake, a high-protein diet or a high-methionine diet, but decreased after long-term protein deprivation. Short-term dietary restriction had a similar effect on methionine absorption in jejunum and ileum, though less pronounced in the latter. The rate of absorption of dimethionine was less influenced by dietary changes than that of methionine.

4. Under all conditions studied, the absorption rate of methionine was greater when presented as the dipeptide than when presented as the equivalent amount of free amino acid. This confirms that dimethionine is taken up intact from the intestinal lumen, and it seems likely that there are different mechanisms of mucosal uptake for methionine and its dipeptide.

1. Pigs from 20 to 60 kg live weight were fed on cereal diets, supplemented only with vitamins and minerals, with and without supplementary lysine.

2. Growth rate, feed:gain ratio and carcass quality of pigs given a high-barley diet (75% barley meal, 23% wheat offal) were inferior to those of pigs given a high-wheat offal diet (75% wheat offal, 23% barley meal).

3. On both diets, but particularly on the high-barley diet, performance was improved by the addition of L-lysine (to give a total lysine content of 5.2 g/16 g nitrogen, approximating to that present in a standard barley meal–wheat offal diet supplemented with 7% white fish meal).

4. Percentage N retention was improved on both diets by supplementation with lysine.

5. Results for carcass composition showed that the carcasses of pigs fed on the unsupplemented high-wheat offal diet contained more lean tissue than those of pigs given the unsupplemented high-barley diet. Lysine supplementation resulted in an increased content of lean tissue on both diets, the percentage increase due to lysine being greater (but not significantly so) on the high-barley diet. The increased lean content was reflected in the carcass measurements but not in the total N retention values, which did not differ significantly between treatments.

6. The results are discussed in relation to the shortage and high cost of animal protein concentrates and the possible replacement of these concentrates with synthetic amino acids.

1. To obtain a quantitative model for nitrogen pathways in sheep, a study of ammonia and urea metabolism was made by using isotope dilution techniques with [15N]ammonium sulphate and [15N]urea and [14C]urea.

2. Single injection and continuous infusion techniques of isotope dilution were used for measuring ammonia and urea entry rates.

3. Sheep were given 33 g of chaffed lucerne hay every hour; the mean dietary N intake was 23.4 g/d.

4. It was estimated that 59% of the dietary N was digested in the reticulo-rumen; 29% of the digested N was utilized as amino acids by the micro-organisms, and 71% was degraded to ammonia.

5. Of the 14.2 g N/d entering the ruminal ammonia pool, 9.9 g N/d left and did not return to the pool, the difference of 4.3 g N/d represented recycling, largely within the rumen itself (through the pathways: ruminal ammonia → microbial protein → amino acids → ammonia).

6. Urea was synthesized in the body at a rate of 18.4 g N/d from 2.0 g N/d of ammonia absorbed through the rumen wall and 16.4 g N/d apparently arising from deamination of amino acids and ammonia absorbed from the lower digestive tract.

7. In the 24 h after intraruminal injection of [15N]ammonium salt, 40–50% of the N entering the plasma urea pool arose from ruminal ammonia; 26% of the 15N injected was excreted in urinary N.

8. Although 5.1g N/d as urea was degraded apparently in the digestive tract, only 1.2g N/d appeared in ruminal ammonia; it is suggested that the remainder may have been degraded in the lower digestive tract.

9. A large proportion of the urea N entering the digestive tract is apparently degraded and absorbed and the ammonia incorporated in the pools of nitrogenous compounds that turn over only slowly. This may be a mechanism for the continuous supply to the liver of ammonia for these syntheses.

10. There was incorporation of 15N into bacterial fractions isolated from rumen contents after intraruminal and intravenous administration of [15N]ammonium salts and [15N]urea respectively.

11. A model for N pathways in sheep is proposed and, for this diet, many of the pool sizes and turn-over rates have been either deduced or estimated directly.