1. Reduced intake of energy or protein per se decreased riboflavin requirement of the chicks under restricted feeding regimens.

2. In severe riboflavin deficiency (2·26 mg/kg diet), efficiency of utilization of both energy and protein was decreased significantly under ad lib. conditions of feeding.

3. Efficiency of utilization of energy (but not protein) was decreased significantly in border-line riboflavin deficiency (3·02 mg/kg diet), when chicks were fed ad lib.

4. Efficiency of protein utilization was decreased significantly in severe riboflavin deficiency when chicks received an energy-restricted diet supplying 80, 70 or 60 yo of the energy intake of the controls.

5. Neither energy nor protein utilization was affected by riboflavin deficiency when both energy and protein were restricted to 70 yo of that consumed by chicks fed ad lib. However, the riboflavin deficiency produced characteristic deficiency symptoms, namely heterophilia, curled-toe paralysis, and reduction in concentration of liver riboflavin.

1. Twenty herbages at different stages of maturity containing from 0·77 to 5·23 g nitrogen/100 g organic matter were harvested, and green herbages were rapidly frozen and stored at - 1·5°. Each herbage was offered at levels approximating to ad lib. to a group of three sheep, individually penned. Intake, digestion and retention of N were studied during a 10 d collec-tion period after a 9 d preliminary period.

2. General regressions relating apparently digested N (NA, g/d), urinary N excretion (UN, g/d) and retention of N (NR, g/d) to N intake (NI, g/d) were established: NA= 0·88NI-3·25 (±1·14; SEb = ±O·013); UN = 2·48+0·35 NI+O·0049 NI2 (±3·09; SEb1, =±0·156; SEb2 = ±0·003); NR = 0·25 NI- 1·92 (±2·40; SEb = ·o·029). These equations accounted for 99% of the variability in N apparently digested, 86% of the variability in urinary N excreted, and 63 % of the variability in N retained.

3. Concentrations of ammonia and trichloroacetic-acid-precipitable N in the reticulo-ruminal digesta and of urea and a-amino-N in plasma were determined immediately before feeding, and at I and 4 h after feeding. Relationships between concentrations of metabolites in the reticulo-ruminal digesta and in plasma, and N intake, N apparently digested, urinary N output and retained N were examined. Estimates of urinary N loss and of retained N based upon metabolite concentrations at individual sampling times were characterized by high residual variabilities. Error terms were in some instances reduced significantly when both thebasal (before feeding) metabolite concentrations and the increments in metabolite concentra-tions after feeding were included in the one equation. The best relationships, based on plasma urea concentrations, accounted for only 74 % of variability in urinary N output.

4. In multiple regressions a significant portion of the variability in urinary N output and in retained N which was not accounted for by N intake could be accounted for by inclusion of metabolite values.

5. The concentration of urea in plasma was the most effective basis for prediction of N utilization. However, no prediction equation accounted for more than 90% of the total variabilityin N output, and no equation accounted for more than 71 % of the total variability in N retention. The feasibility of developing techniques for examination of efficiency of N utilization by a particular class of animal, based upon digesta and plasma metabolite con-centrations is discussed.

1. Eighteen bull calves, comprising twelve Ayrshires, three Friesians and three Jerseys were reared from birth to a slaughter weight equivalent to 22 % of mature cow weight of the breed.

2. All the calves were given a milk substitute diet ad lib. in two feeds daily. Six of the calves received this diet alone and the remaining twelve calves were offered roughage ad lib. from I week of age, either as meadow hay or as barley straw. The calf-house was maintained at a mean temperature of 23' and a mean relative humidity of 62 %.

3. The mean total intake of meadow hay and barley straw over the experimental period of about 12 weeks was 3.0 kg and 0.4 kg respectively. Only three calves were consuming any meadow hay and only two calves any barley straw at 7 weeks of age.

4. The roughage consumed had no effect on the incidence of diarrhoea, on dry-matter intake from milk or on live-weight gain. All the calves offered meadow hay had lung lesions at slaughter. Severity of lung lesions in the Jersey and Friesian calves combined, but not in the Ayrshires, tended to be inversely related to the relative humidity to which they were exposed.

5. Dressed carcass weight and killing out percentage tended to be lower for the calves offered meadow hay. There was a highly significant inverse relationship between total intake of hay and killing out percentage. Perirenal fat depositionin relation to carcass weight was significantly lower and carotenoid content of the fat significantly higher for the calves offered the meadow hay. Skin weight per unit of slaughter weight 0.78 or carcass weight OJ* was significantly greater for the calves given the milk substitute diet only.

6. It is concluded that the calf shows very little desire to eat roughage when given a good- quality milk substitute diet ad lib. and that, even when the amounts of roughage consumed are small, this has a deleterious effect on carcass quality.

1. Eighty bull calves, comprising forty-eight ayrshire and sixteen each of the Friesian and Jersey breeds, were used in a randomized block experiment. Forty calves were maintainted at a mean environmental temperature of 21° and forty at 14·5°. Within each temperature, twenty calves were reared from birth on a liquid milk substitute diet (pre-ruminant calves) and twenty were weaned at 35 d of age on to dry food (ruminant calves). Each type of diet was gien either ad lib. or at a restricted level. The calves were slaughtered at about 100 d of age.

2. The incidence of a high rectal temperature (> 39·39°) was greater for the pre-ruminant than for the ruminant calves during the first 14 d of life and throughout the whole experimental period, and was higher for calves at an enviromental temperature of 21° than for thosekept at 14·5°. During the experimental period as a whole, but not during the first 14 d of life, the incidence of diarrhoea was greater for the pre-ruminant calves. Mean rectal temperature was higher for the pre-ruminant calves and also higher for the calves reared at the high environmental temperature.

3. The incidence of lung lesions at slaughter was significantly higher in the ruminant than in the pre-ruminant calves, and tended to be higher at the high environmental temperature. There was a highly significant positive relationship between severity of lung lesions and incidence of a high rectal temperature (> 39·33°) and mean rectal temperature. Jersey and Friesian calves, but not Ayrshire calves, showed increased severity of lung lesions with increasing relative humidity at the low environmental temperature. When the results at the 'high' environmentaltemperature were combined with those obtained in an earlier experiment, the severity of lung lesiogs for Jersey and Friesian calves increased with decreasing relative humidity. At the ‘high’ but not at the ‘low’ temperature, severity of lung lesions was inversely related to skin weight/kgO·73.

4. Live-weight gain was much lower for the ruminant calves, but was unaffected by environ-mental temperature. Daily dry-matter intake from liquid diets given ad lib. did not differ be-tween breeds at the same live weight. In contrast, daily dry-matter intake from dry food given ad lib. was greatest for the Jersey and lowest for the Friesian at the same live weight. The same daily dry-matter intake from liquid as from dry diets was achieved at similar percentages of mature weight for the three breeds. Relative weight gain within type of diet was similar for Jersey and Ayrshire calves, but tended to be higher for the Friesian calves.

5. Carcassweight, carcass weight0·73, perirenal fat deposition, skin weight and killing out percentage were much lower for the ruminant calves. When adjusted for differences between treatment means for carcass weight0·73, perirenal fat deposition was greater at the ad lib. levels of intake and was 36% greater for pre-ruminant calves given milk substitute ad lib. at an environmental temperature of 21° than for those maintained at 14·5°.

6. It is concluded that there is no advantage to be gained from rearing calves at an environ mental temperature above 14·5°, unless increased fat deposition is required in veal calves.

1. Previous publications by the author and his colleagues have provided extensive records, and additional ruminating behaviour of cows receiving a wide range of diets. These recoreds, and additional unpublished records, have been used to justify a proposed index of the physical property of fibrousness, or roughage, in diets for ruminants.

2. It is proposed that the total time spent by ruminants in chewing their food, during eating and during ruminating, should be the basis of the basis of the roughage index

3. Experssion of the roughage index as total time spent chewing per kg dietary dry matter largely eliminates differences resulting from variation in the amount of food consumed, and differences resulting from the time of access to the food.

4. Examples of the proposed roughasge index are given. The values range from 145 to 191 min/Kg dry matter for oat straw ot under 20 min/kg dry matter for diets of concentrates or of finely ground herbages; hays and silages tend to fall in the region of 90–110 min/kg dry matter. Values for the indx increase with dietary proportaions of hay or straw.

1. Experiments were done to find whether the rat liver can be maintained in a satisfactory condition when perfused with oxygenated Krebs-Ringer bicarbonate buffer without added protein or red cells.

2. The condition and preformance of the liver in this system were assessed from measurements made to ascertain its general condition or viability, its basal characteristics and its response to added substrates.

3. It was found that the rapid flow-rate of the medium through the livers and the efficient oxygenation of the medium ensured that enough oxygen was available for the livers to deal with large quantities of added lactate.

4. The potassium concentrations in the livers and the rates of alanine aminotransferase (EC 2.6.1.6) from the cells during perfusion, and the water content after perfusion showed that the livers were not grossly damaged and that they did not deteriorate measurably for up to 3 h of perfusion.

5. Liver oxygen consumption, ATP concentrations, lactate and pyruvate concentrations and ratios, and rates of urea and glucose synthesis and bile secretion, all in perfusions without added substrate, were either similar to measurements by other workers from livers perfused withmedia containingred cells and protein or were reasonable extrapolations from availabledata.

6. The rates of glucose production from lactate, and urea and glucose output from amino acids indicated that the liver responds adequately to added substrates.

7. Measurements of amino acid concentrations in perfusate indicated that the livers of rats starved for 18–20 h regulated the amino acids to characteristic levels, by overall output or uptake, except for valine, leucine and isoleucine which were continuously given out into the medium. The results suggest that in vivo there is a general flow of most of the amino acids from extrahepatic tissues to the liver during fasting, while valine, leucine and isoleucine flow from liver to extrahepatic tissues.

8. When pentobarbitone sodium (Nembutal) was used as the anaesthetic for removal of the liver from the donor rat, the rates of urea and glucose output in perfusions without added substrates were lower than when halothane (Fluothane) was used, indicating that pentobarbitone has an inhibitory effect on these measures of liver function during the subsequent perfusion.

1. The effects of breast-feeding and artificial feeding have been analysed for a group 250 infants from lower socio-economic, urban families in Kuala Lumpur, Malaysia.

2. The factors considered were the ethnic group, the sex of the infant, the size and income the family and the type of milk fed. No infant in the study was given ‘non-milk’ feeds before the age of 40 weeks.

3. The effects of these factors on the weight gains and the number of reported illnesses up to the age of 40 weeks have been analysed.

4. At no time in the first 40 weeks did breast-fed infants gain weight significantly more rapidly than artificially fed infants. After the age of 20 weeks, artificially fed infants gained significantly more weight than breast-fed infants.

5. The type of feeding had no statistically significant effect on the frequency of minor respira-tory or alimentary illnesses.

6. In this community, the welfare of the family often depends on the earnings of the mother, who has to make the choice between breast-feeding and paid employment. In the group studied, breast-feeding appears to offer no advantages over artificial feeding. The principle guiding the Maternal and Child Health staff when advising the mother should be the welfare of the whole family.

1. Male and female guinea-pigs with high tissue concentrations of L-xyloascorbic acid (ascorbic acid, AA) and male guinea-pigs with high tissue concentrations of D-araboascorbic acid (isoascorbic acid, isoAA) were given a scorbutogenic diet and the rates of depletino from various tissues were measured fro both isomers.

2. The loss of AA from the brain and eye lens was considerably less rapid than the loss from the adrenal glands, spleen and aqueous humour. After 14nd on the AA-free diet the AA concentrations in the brain and eye lens were 24 and 27% respectively of the initial concentrations; the corresponding values for the aqueous humour, adrenal glands and spleen were 3,4 and 5%. There was no apparent sex difference in the rate of loss of AA.

3. The loss of isoAA was much more rapid than that of AA in the spleen, adrenal glands and aqueous humour; in the brain and eye lens the depletion patterns of the two isomers were similar.

1. Two experiments involving 106 lambs were conducted to study the functioning of the oesophageal groove reflex in lambs sucking from either individual feeders or from a bulk dispenser. The effects on the performance of lambs given either a high-protein or a low-protein creep feed in conjunction with either a ewe's milk substitute, Ewelac, or a homogenate of calcium caseinate, Casilan, were studied. Two milk substitutes, one with a long and one with a short clotting time were compared in terms of their effects on the incidence of diarrhoea.

2. The location of the liquid feeds in the stomach was studied radiologically.

3. In both experiments the sucking behaviour of the lambs was closely related to thefunctioning of the oesophageal groove reflex and performance of the lambs. In the first experi-ment the milk substitute consistently entered the abomasum in seven of the ten individually fed lambs and in twelve of the twenty-two group-fed lambs. The corresponding figures for the second experiment were twenty-two of the twenty-four individually fed and thirty-four of the fifty group-fed lambs.

4. When the milk substitute entered the abomasum it always did so throughout the fattening period even in those instances where the milk had been withheld for 1 month.

5. Poor sucking, low milk consumption and the entry of the milk into the rumen resulted in very poor performance by the lambs. Such lambs demonstrated a non-specific unthriftiness similar to the ‘tail enders’ sometimes observed with lambs reared with ewes.

6. Continued feeding with either the milk substitute or casein homogenate with a low-protein creep feed did not improve performance.

7. The clotting time of the milk substitute did not appear to influence the incidence of diarrhoea among the lambs.

1. The introduction of certain tertiary branched-chain carboxylic acids into the rumen of sheep, either by continuous infusion or by direct incorporation of the acids in the concentrate food mixture, had no effect on the oxygen consumption or carbon dioxide production of the sheep. Methane production was depressed, the extent of the depression increasing with the molecular weight of the carboxylic acid.

2. There was a small decrease in the apparent digestibility of the food and a small increase in urinary energy output.

3. There was no significant increase in the metabolizable energy intake of the sheep. There was, however, a small increase in the amount of energy stored in the body. This small increase was about 84 % of the gross energy of the branched-chain acids added.

4. It is concluded that any practical advantage to be gained from the addition of branched-chain carboxylic acids to the diet of ruminants remains unproven.

1. Total body iron and some of its subfractions, i.e. haem iron, non-haem iron and ferritin iron, as well as ferritin were measured in groups of newborn rats and of rats aged 4,15 and 24 d.

2. Iron accumulated in the rats throughout suckling, with slightly more going into the haem than into the non-haem fraction.

3. Per unit body-weight, haem iron was maintained well throughout the study period but total body iron and non-haem iron were both significantly diminished at 15 d.

4. Within the non-haem fraction, ferritin iron was severely diminished at both 15 and 24 d, but the non-ferritin portion of non-haem iron was increased.

5. The results were interpreted in terms of the relationship between the growth of body mass and the supply of iron to the young animal.

1. The effect of the extent of ruminal fermentation of starch on the postruminal digestion of starch and protein was investigated in sheep, differences in rumen fermentation being obtained by giving diets based on barley, maize, or maize plus sodium chloride. The mean percentages of starch (α-linked glucose polymers) fermented in the rumen wert 91, 79 and 78 respectively with these diets, but there was considerable variability, particularly with the maize diets.

2. When large amounts of starch escaped fermentation in the rumen, substantial quantities passed the terminal ileum and were mostly fermented in the large intestine; the greatest amount of starch found in the faeces was 2 % of intake.

3. A decrease in the extent of rumen fermentation of starch was associated with a decrease in the concentration of crude protein and of diaminopimelic acid (DAPA) in the abomasal fluid, but there was no difference in quantity of crude protein disappearing from the small intestine. The concentration of DAPA was greater with the barley diet than with the maize diet, indicating that more dietary protein, originating from maize than from barley, escaped the rumen un-degraded. This conclusion was supported by a greater similarity between the amino acid composition of the abomasal fluid and the diet when maize was given.

1. The relative rates of passage of polyethylene glycol (PEG) and lignin through the alimentary tracts of sheep were examined through the ratio of these two markers in the fodder and in the contents of various segments of the gut. A much faster turnover of PEG than of lignin in the stomach compartments suggested that samples from these organs could not be representative of the digesta flowing through them. Average PEG:lignin ratios in the small and large intestines were close to the ratio in the fodder, indicating that sampling from the duo-denum in the living animal could possibly yield material representative of that flowing from the stomach to the small intestine. Similar results were obtained for high and low levels of fodder intake.

2. A procedure was developed for automatic sampling from the duodenum for prolonged periods, and the material collected was shown to be representative of digesta flow. Simpler methods of sampling from the duodenum were shown to be liable to relatively large errors.

3. The amount of nitrogen reaching the duodenum in sheep given lucerne hay pellets was found to be equivalent to practically 100 % of the dietary N, whether the intake of fodder was 600 g/d or 1500 g/d.