1. A method of continuous alimentation of cattle by total infusion of nutrients has been developed. Friesian steers within the weight range 100–400 kg live weight and dairy cows were used.

2. A multi-channel peristaltic pump was used to infuse solutions of volatile fatty acids (VFA), minerals, and buffer through a cannula in the rumen and a case in–vitamin solution into the abomasum.

3. The method described was successfully used with two cows and four steers in a series of trials over intervals of approximately 2 months. The levels of infusion were up to twice maintenance and with various relative proportions of VFA and protein. Blood metabolite levels, rumen osmotic pressure and pH were monitored and effectively controlled.

1. Expt 1. Forty 200 kg heifers were given wheat straw ad lib. plus one of five pelleted supplements, each of which supplied 40 g/nitrogen as urea/d, Treatment A did not supply other sources of N, and other treatments supplied daily 40 g digestible N as casein and formaldehyde-treated casein (HCHO-casein) in the following proportions (w/w): 100:0 (B), 70:30 (C), 30:70 (D), 0:100 (E). After 5 weeks (period 1) all supplements were withdrawn from half (four) of the animals in each treatment group (NS) over a period of 8 weeks (period 2). At the end of period 2. N balances were measured in four animals on each of treatments E and NS.

2. In period 1 the mean intake of straw by animals on treatments D and E was higher than the mean intake by animals on treatments A, B and C (3·32 v. 2·83 k/d respectively, P < 0·01) and live-weight changes also differed significantly (+ 72 and – 126g/d respectively: P < 0·01). Intakes of straw in period 2 were 3·74 and 3·20 kg/d for animals with and without supplements respectively (P < 0·01) and live-weight changes were +110 and – 157 g/d on the respective treatments (P < 0·01). For animals receiving supplements in period 2, intakes of straw did not differ significantly between supplements; live-weight changes were −14 g/d on treatment A and +141 g/d on treatments B, C, D and E (P < 0·01).

3. N balances on treatments E and NS were +11·4 and – 3·3 g/d respectively (P < 0·01), although digestibility of organic matter (OM) was similar on the two treatments.

4. Expt 2. Four 185 kg steers with rumen and abomasal cannulas were given wheat straw ad lib. plus one each of treatments A, B and E in a randomized block sequence. Dry matter (DM) intakes were 3·44, 3·89 and 4·05 kg/d on treatments A, B and E respectively (P < 0·05). N intakes were 29 and 37 g/d higher on treatments Band E respectively than on treatment A, but abomasal flows of N were only 4 and 14 g/d higher on the respective treatments. The latter value indicates that approximately 0·62 of HCHO-casein was degraded in the rumen. Efficiencies of bacterial protein synthesis were 31, 24 and 26 g bacterial N/kgOM apparently digested in the rumen (P > 0·05) on treatments A, B and E respectively.

5. It was concluded that efficiency of bacterial protein synthesis in the rumen was not limited by the supply of peptides and amino acids, and that protein supplements do not consistently stimulate intake of low-quality roughages when requirements for rumen degradable N have been met. Higher flows of N to the intestines when HCHO-casein, and to a lesser extent casein, were given were associated with a shift from negative to positive live-weight changes. These live-weight changes were not significantly correlated with DM intakes from which it appears that effects of casein supplements on live weight may have been attributable to effects of absorbed amino acids on efficiency of tissue protein synthesis either directly or through gluconeo genesis.

1. A procedure for measuring methane production by rumen contents incubated anaerobically in vitro is described. Assessments of methane production in vivo, in both sheep and cattle, were made by withdrawal of rumen contents and measuring their capacity to produce methane in vitro.

2. Many members of a series of 6-substituted 2,4-bis (trichloromethyl)-benzo[1,3]dioxins were potent inhibitors of methanogenesis by rumen contents in vitro. The most potent compound inhibited methane production by 70% or more at a concentration of 1 μg/ml (approximately 2.5 μmol/l).

3. Two compounds, namely the 6-carboxylic acid (IC1 13409) and the 6-carboxamide (ICI 43586), caused a large inhibition of methanogenesis sustained for many hours, following a single intrarumen injection in sheep or cattle. Inhibition was maintained for long periods by single daily dosing directly into the rumen or by dietary administration.

4. In a 28-week growth trial in beef cattle inclusion of ICI 13409 in the concentrate element of the diet, at a level of 6 mg/kg body-weight, improved live-weight gam by 8·0% (P < 0·05) with respect to untreated animals whilst reducing food intake by 5·0% (P < 0·05). Smaller and not statistically-significant effects were seen with this compound at 3 mg/kg body-weight and with the antibiotic monensin(Romensin; ElancoPLC). All treatments significantly improved the retention of dietary energy into the carcass, offal and intestinal tracts of the trial animals and significantly reduced the quantity of methane eructed into expired gases.

1. The increase in activation coefficient (stimulated: basal activity) of erythrocyte NAD(P)H2:glutathione oxidoreductase (EC 16.4.2) and reduction in hepatic flavin concentration which occurred in riboflavin-deficient weanling rats were not markedly or consistently affected by differences in the concentration of lipid in the diet nor by differences in the total proportion of saturated or polyunsaturated fatty acids in the dietary lipid.

2. Their gain in body-weight was, however, reduced when the dietary lipid concentration was increased from 30 to 200 g/kg and liver: body-weight and hepatic triglyceride content were correspondingly increased, suggesting a functionally-deleterious effect of high fat intake in the deficient animals. This was especially severe when the diets contained cottonseed oil, which appeared to be toxic for the deficient animals.

3. Comparisons between fatty acid profiles of hepatic phospholipids of deficient, pair-fed and ad lib.-fed control animals indicated that the increase in proportion of 18:2 ω6 and the decrease in proportion of 20:4 ω6 observed in deficient animals were due specifically to riboflavin deficiency, whereas certain other changes were probably caused by inanition. The changes in 18:2ω6 and 20:4 ω6 were observed at both low and high levels of lipid intake and at both low and high levels of dietary lipid polyunsaturation. Similar changes in fatty acid profiles were observed in renal, erythrocyte membrane, and plasma phospholipids, but were not seen in cardiac phospholipids.

4. A consistent increase in proportion of 18:2 ω6 was also observed in the hepatic triglycerides, together with a decrease in proportion of 16:0.

5. It is concluded that acute riboflavin deficiency affects lipid metabolism in a characteristic manner, probably by interfering with β-oxidation of fatty acids, but that diets of high lipid content do not significantly increase the extent of flavin depletion.

1. Oxygen consumption was measured by means of an O2 electrode in mitochondrial suspensions from riboflavin-deficient and pair-fed control rats, using six different substrates. Whereas consumption of O2 by glutamate was only slightly depressed in mitochondria from deficient animals, the consumption of O2 by hexanoate and by palmitoyl-L-carnitine was depressed to approximately half the control value: a highly significant difference. A comparable magnitude of depression was observed for stearoyl-, oleoyl-, and linoleoyl-L-carnitine. There were no major or consistent differences between groups of animals receiving two different types, and two different levels, of fat in their diet.

2. The activity of acyl coenzyme A dehydrogenase (EC 1.3.99.3) in hepatic mitochondrial fragments, measured by cytochrome c reduction with palmitoyl-coenzyme A as substrate, and expressed as maximum velocity (Vmax) With respect to phenazine methosulphate, was also reduced to approximately half the control value in deficient animals.

3. In hepatic microsomes, cytochrome b5 reductase( EC 1.6.2.2) activity was unaffected by riboflavin deficiency, although NADPH-cytochrome c reductase (EC 1.6.2.4) and microsomal flavin content were diminished to approximately half the control values. Acyl CoA (Δ9) desaturase activity (EC 1.14.99.5) was virtually identical in deficient, pair-fed, and ad lib.-fed control groups.

4. It is concluded that the depression of mitochondrial β-oxidation of fatty acids which is observed in riboflavin-deficient animals is not a secondary result of inanition, and may account for the observed changes in fatty acid profiles of triglycerides and phospholipids. Failure of the microsomal fatty acid desaturation system is less likely to be a major consequence of riboflavin deficiency.

1. The physiological response of rainbow trout (Salmo gairdneri) reared on different levels of available carbohydrate in practical trout diets having the same levels of energy and nitrogen for 16–24 weeks was determined.

2. Weight gain was significantly reduced in trout reared on the highest level of available carbohydrate, 210 g cerelose (α-glucose)/kg, and there was a significant linear regression (R2 0.88) of dietary carbohydrate on weight gain.

3. Liver: body-weight values and liver glycogen levels increased in relation to increased dietary carbohydrate.

4. Liver glucose-6-phosphate dehydrogenase (EC 1.1.1.49) activity increased and liver phosphoenolpyruvate carboxykinase (EC 4.1.1.32) activity decreased per kg body-weight of fish with increasing dietary carbohydrate. However, no significant effect was noted on the activity of these liver enzymes above a dietary cerelose level of 140 g/kg.

5. Liver fructose diphosphatase (EC 3.1.3.11) activity increased with increasing dietary carbohydrate has been interpreted as meaning a recycling of triosephosphate to glucose-6-phosphate.

6. Dietary carbohydrate level had no significant effect on the liver pyruvate kinase (EC 2.7.1.40) activity, the rate of glucose utilization or the percentage conversion of [14C]alanine to glucose in the plasma of trout.

7. The results indicate that rainbow trout have a limited ability to adapt to increased dietary carbohydrate and a level in excess of 140 g/kg of the diet is not efficiently utilized.

1.In order to assess the effects of oestrogens on the metabolism of tryptophan and vitamin B6, ovariectomized rats have been maintained on diets providing known amounts of tryptophan, nicotinamide and vitamin B6. They received oestrone sulphate. 210μg/kg body-wt per d, either incorporated in the diet for 8 weeks, or by daily intraperitoneal injection for periods of 1–3 d.

2. Oestrone sulphate administration caused a slight reduction in the concentration of pyridoxal phosphate in plasma. It had no effect on the concentration of pyridoxal phosphate in liver or kidney, the urinary excretion of 4-pyridoxic acid, the activation of erythrocyte aspartate aminotransferase (L-aspartate:2-oxo-glutarate aminotransferase, EC 2.6.1.1)by incubation with added pyridoxal phosphate, or the activity of pyridoxal oxidase (aldehyde:oxygen oxido-reductase, EC 1.2.3.1) in the liver.

3. Oestrone sulphate administration caused an increase in the urinary excretion of kynurenine and a reduction in the activity of liver kynureninase (L-kynurenine hydrolase, EC 3.7.1.3), It had no effect on the urinary excretion of N1-methyl nicotinamide or the concentrations of nicotinamide nucleotides in blood, liver or kidney.

4. There was a considerable excess of the apoenzyme of kynureninase in the liver. Incubation of liver homogenates with added pyridoxal phosphate led to a 4- to 5-fold increasein activity.

5. We conclude that there is no evidence of any significant effect of oestrogens on vitamin B6. It is suggested that abnormalities of tryptophan metabolism in women receiving oestrogens. which have been widely attributedto drug-induced vitamin B6 depletion, can be accounted for by inhibition of kynureninase by oestrogen metabolites.

1. Three isoenergetic test diets containing 320, 430 and 530 g protein/kg, with (experimental) and without (control) inclusion of an anabolic steroid, ethylestrenol, were given to rainbow trout (Salmo gairdneri) of mean initial weight 27 g, for 60 d.

2. After 60 d, all trout groups were given an identical, steroid-free, commercial diet (410 g protein/kg) for a further 30 d, to observe withdrawal effects on growth.

3. The weight and length of trout given the 430 and 530 g protein/kg control diets were significantly greater after 60 d than those given the 320 g protein/kg control diet.

4. Inclusion of steroid enhanced the weight and length of trout given the 320 and 430 g protein/kg experimental diets, exerting a preferential effect on weight as opposed to length.

5. After steroid withdrawal, a significant difference between the weight and length of the 320 g protein/kg control and experimental groups was still apparent.

6. An increase in dietary protein increased the food conversion efficiency, and decreased the protein efficiency ratio. Inclusion of steroid increased both these factors over the respective controls.

7. Protein assimilation decreased, and faecal nitrogen content increased with increasing dietary protein. In trout given steroid, protein assimilation and apparent digestibility was higher, and facecal N content, lower than the controls.

8. Muscle protein increased with increasing dietary protein, and was higher in trout given steroid.

9. Relative liver weight increased with increasing dietary protein. Inclusion of steroid resulted in a reduction in relative liver and gut weight, and an increase in kidney weight.

10. It is concluded that ethylestrenol promotes both the growth and efficiency of nutrient utilization of trout. The magnitude and duration of these effects are a function of the dietary protein level.

1. Cattle were maintained by intragastric infusion to see how much nitrogen was excreted on protein-free diets.

2. Minimal N excretion was estimated with two dairy cows in three periods, i.e. when they were non-pregnant and non-laclating, when they were between 117 and 133 d pregnant and when they were between 220 and 233 d pregnant. The minimal N excretion was also estimated on two occasions with two steers when their average live weights were 200 and 350 kg.

3. Average urinary N excretion without protein infusion was 298, 305 and 283 mg/kg metabolic live weight (W0·75) for the non-pregnant cows and for cows during the first and second periods of pregnancy respectively; total N excretion including the faecal N was 340, 329 and 319 g/kg W0·75.

4. For steers the urinary N values were 403 and 295 mg/kg W0·75 at 200 and 350 kg live weight respectively and total N excretion including faecal N was 408 and 320 mg/kg W0·75.

5. Urinary excretion of creatinine was the same for animals given casein via the abomasum as a source of protein or given no protein with mean values for the cows of 13·6 and 14·9 g/d for the first and second stages of pregnancy respectively. Mean values for the steers were 6·5 and 7·6 g creatinine/d at 200 and 350 kg live weight respectively.

6. It is suggested that the so-called metabolic faecal N in ruminants, estimated with N-free diets, is mainly endogenous N derived from tissue breakdown of protein but incorporated in microbial debris and excreted in the faeces.

1. Certain digestive and metabolic criteria were examined in mature wethers before and following (1) a simple exploratory laporotomy (two sheep), (2) establishment of a rumen cannula plus simple (‘T’-shaped) cannulas in the duodenum and ileum (six sheep), (3) establishment of a rumen cannula plus two cannulas in the caecum (four sheep), (4) establishment of a rumen cannula plus re-entrant cannulus in the duodenum and ileum (four sheep) and (5) insertion of catheters into both external jugular veins (four sheep).

2. Metabolizability of a standard ration and nitrogen balance and rumen retention time of the sheep were not significantly changed by any of the surgical procedures carried out.

3. The amount of heat produced per unit metabolic weight of the sheep prepared with re-entrant cannulas increased significantly (21±5·6%; P < 0·001).

4. The use of the different preparations in digestive and metabolic studies is discussed.

1. The effect of confinement stress on the metabolism of vitamin A was studied in ratsby following changes in tissue distribution of the vitamin for 29 d. In order to minimizepredicted errors which might result from fluctuation of vitamin A intake, the effect of the stress was investigated in rats fed on a vitamin A-free diet.

2. Daily stress for 6 h induced an enlargement of the adrenals with a concomitant involution of the thymus and spleen, values returning to normal within 11–15 d.

3. The stress caused an immediate decrease in the content of vitamin A in serum.

4. Feeding rats a vitamin A-free diet resulted in a significant increase in the vitamin Acontent of the kidney. Imposing stress on these rats inhibited markedly the increase in kidney vitamin A content.

5. The stress produced no appreciable change in levels of the vitamin in the liver andtestes.

6. There was a preferential accumulation of the vitamin in the adrenals of the stress-imposed rats even though they were fed on a vitamin A-free diet.

7. In conclusion, the results of the present study demonstrated that chronic immobilization stress produced marked tissue-dependent changes in their vitamin A content.

1. The removal of the interscapular brown adipose tissue (IBAT) led to an increase in body-weight of normal, lean mice as compared to anaesthetized controls.

2. No significant difference in food consumption could be detected between the two groups of mice over the period of the experiment.

3. Fat extraction of the whole carcasses with chloroform: methanol showed a statistically significant increase in fat content in the animals without IBAT.

4. There was no apparent failure in the operated animals to sustain core temperature when exposed to a cold stress situation (4° for 24 h).

5. There was no difference in the wet weight, protein content or cytochrorne oxidase content of the dorso-cervical brown adipose tissue (DCBAT) between operated and control mice. This is indicative of a lack of proliferation of other brown adipose tissue sites in the operated mice in response to the removal of the IBAT.

6. It is suggested that brown adipose tissue is implicated in dietary themiogenesis in the mouse.