1. Iron retention in adult male rats given 3 g dried ground peas, immature and mature (Pisum sarivum cv Dark-skin perfection) and leafless (Pisum sativum cv Filby), extrinsically labelled with 0.25 μCi 58Fe, was measured by whole-body counting. The Fe was less well absorbed (P < 0.01) from the mature peas (0.251 (SE 0.021)) than from the immature (0.384 (SE 0, 032)) or leafless peas (0.344 (SE 0.026)).

2. The availability of Fe from the leafless peas was compared with that of defatted soya-bean flour by the same technique. Significantly more Fe (P < 0.005) was retained from the pea flour (0.471 (SE 0.013)) than from the soya-bean flour (0.377 (SE 0.022)).

3. The effect of adding pea testa to bread (97.6 g/kg dry weight), as in the production of high-fibre white bread, on Fe availability was measured and compared with the availability of ferrous sulphate in young and adult male rats. There were no significant differences between the high-fibre and low-fibre breads in either age-group, although the older rats absorbed less Fe from all three sources. Retention from high-fibre bread, low-fibre bread and FeSO4 was as follows (mean with SE): young rats 0.452 (0.037), 0.475 (0.040) 0.541 (0.032); mature rats 0.363 (0.034), 0.366 (0.030), 0.471 (0.028).

4. It was concluded that the addition of pea testa to white bread does not have a detrimental effect on Fe availability. Immature and leafless peas appear to be a better source of available Fe than soya-bean flour, despite similar fibre levels, but with maturity the Fe in peas is rendered less available.

1. Plasma and urinary selenium were determined among vegans, lactovegetarians and several groups of omnivorous subjects, using gas-liquid chromatography.

2. Plasma Se was lower among lactovegetarians (0.80 (SD 0.18) μmol/l) than in the other groups (0.98 (SD 0.15) μmol/l). This was not related to Se intake, since the vegans had a lower and the lactovegetarians a higher intake of Se than omnivorous subjects in Sweden.

3. Urinary Se was 0.36 (SD 0.10)μmol/d for controls, 0.17 (SD 0.10) μmol/d for vegans and 0.16 (SD 0.07)μmol/d for lactovegetarians. No relation between dietary Se and urinary Se was observed. Among vegetarians, plasma Se and urinary Se were correlated (r 0.51; P < 0.05).

1. The volume of adipocytes in two intra-orbital sites and fourteen superficial and intra-abdominal sites, and the total adipocyte complement have been measured in virgin and reproductive guinea-pigs maintained on several different regimens of diet and exercise.

2. The adipocytes around the ocular muscles at the back of the orbit (peripheral fat) are always larger than those just behind the eyeball (orbital fat).

3. The adipocytes in both the intra-orbital sites are significantly larger in guinea-pigs whose total adipocyte complement is smaller than one standard deviation from the mean, than in those which have a normal-size or large adipocyte complement.

4. The volume of intra-orbital adipocytes correlates very significantly with the volume of adipocytes in superficial and intra-abdominal sites in guinea-pigs which have large adipocyte complements, correlates weakly in those with normal adipocyte complements and not at all in those with small adipocyte complements.

5. It is suggested that there may be fewer intra-orbital adipocytes in animals which have small adipocyte complements, and that, because the intra-orbital adipose tissue occupies a constant volume, the adipocytes in these sites become larger when they are less numerous.

1. The effects of a 100 g/kg substitution of guar gum on the body-weight gain, food consumption and faecal dry weight of mice fed on a high-sucrose diet and on the activities of hepatic glucose-6-phosphate dehydrogenase (EC 1. 1. 1. 49), 6-phosphogluconate dehydrogenase (EC 1. I. 1. 44), malate dehydrogenase (oxaloacetate- decarboxylating) (NADP+) (EC I. 1. 1. 40), ATP-citrate (pro-3S)-lyase (EC 4. I.3.8), 6-phosphofructokinase (EC 2.7. 1. 11), pyruvate kinase (EC 2. 7. 1. 40)and fructose-1, Qbisphosphatase (EC 3. 1. 3. 11) were studied.

2. Guar gum had no effect on body-weight gain or food consumption but increased faecal dry weight.

3. Guar gum increasedtheactivitiesofglucose-6-phosphatedehydrogenase, malatedehydrogenase(oxaloacetate- decarboxylating) (NADP+) and 6-phosphofructokinase expressed on a wet-liver-weight basis.

4. Guar gum increased the activities of glucose-6-phosphate dehydrogenase, malate dehydrogenase (oxaloacetate- decarboxylating)(NADP+), ATP-citrate (pro-3S)-lyase and 6-phosphofructokinase expressed on a liver-protein basis.

5. Guar gum increased the activities of glucose-6-phosphate dehydrogenase and malate dehydrogenase (oxaloacetate-decarboxylating)(NADP+) expressed on a body-weight basis.

6. These results suggest that guar gum increases the flux through some pathways of hepatic lipogenesis when mice are fed on high-sucrose diets.

1. High-fat-high-cholesterol diets containing casein or a Vicia faba bean (faba bean) protein concentrate as the protein source were given to rats for 5 weeks. When the faba bean protein concentrate or its ethanol extract was present in the diet, a marked decrease was found in the level of circulating cholesterol associated with the lower-density lipoproteins (very-low-, intermediate- and low-density lipoproteins) compared with the level found on the diets containing casein or the faba bean protein concentrate deprived of ethanol-soluble factors.

2. Alterations in apoprotein pattern were detected after the different dietary treatments. In particular, apoA-I appeared in an unusual form with electrophoretic mobility faster than normal in all lipoprotein fractions after feeding the diets that did not lower plasma cholesterol. When the diets contained the faba bean protein concentrate or its ethanol extract, the apoA-I disappeared from the lower-density lipoproteins but its normal form and the unusual one were apparent in the high-density lipoproteins.

3. A moderate increase in faecal excretion of acidic steroids was found after feeding the diets containing the ethanol-soluble factors, irrespective of the protein source.

4. The results are discussed in relation to the presence of saponin and polyunsaturated lecithin in the ethanol extract of the faba bean protein concentrate.

1. Newborn rabbits were overfed by encouraging them to suck from two lactating does. These double-fed rabbits were compared with single-fed litter-mate controls.

2. A standard set of fore- and hind-foot radiographs was obtained by taking daily radiographs from a normal litter and selecting the most representative film to act as a standard for that day.

3. Bone age was assessed in single- and double-fed rabbits at ages 7, 14, and 21 d by comparing radiographs taken at these ages with the standard films.

4. Double-feeding was associated with an increase in body-weight and an increase in bone age, although the former was increased to a much greater extent than the latter. The advance in bone age was proportional to an increase in bone length.

5. There is little information available on overnutrition and skeletal maturation in man, but what information is available suggests that height and skeletal maturation are increased in parallel. The present study with rabbits supports the concept that overnutrition increases growth rate but does not disturb the relation hetween bone growth and bone age.

6. Bone age can be assessed very sensitively in rabbits using the previously-described technique. It would therefore be a valuable technique for studying the endocrinology of skeletal maturation.

1. An alternative statistical technique, based on analysis of the 25th percentile, was used to examine teenagers' diets. The technique was developed to identify personal characteristics that affected the prevalence of low energy and nutrient intakes. It provided useful information not obtainable from methods based on average intakes.

2. The study sample was a representative sample of 1055 high-school students in Tasmania, Australia, aged 11–16 years.

3. Among girls, different characteristics had the greatest influence on the prevalence of low intakes (‘low’ being defined as below the 25th percentile for girls). Fatness had the greatest influence for several dietary components. Fatter girls were more likely to have low intakes of energy, carbohydrate, iron, calcium and niacin-equivalent, and also of ‘empty-energy’ foods. School type had the greatest influence for fat, riboflavin and vitamin A. Exercise had the greatest influence for protein, low intakes being more usual among the least active girls.

4. Among boys, height and age generally had the greatest influence on the prevalence of low intakes (‘low’ being defined as below the 25th percentile for boys). Taller and older boys were less likely to have low intakes. This was attributed partly to increased physiological needs, but peer-group influences appeared more important in relation to food choices. Thiamin was unusual, in that recent use of analgesics had the greatest influence on the prevalence of low intakes.

1. Twenty-six gilts were used in an experiment to study the effects of level of feed intake on the growth and chemical composition of the gravid uterus and mammary tissue at several stages of gestation. The animals were given either 1.8 or 2.5 kg feed/d (20 or 30 MJ metabolizable energy (ME) respectively) and were slaughtered at intervals between days 40 and 110 of gestation. The gravid uterus was dissected into fetal, placental, fluid and empty uterus components. From day 70 of gestation the mammary tissue was also dissected. The fresh weight and dry matter (DM), energy and nitrogen contents of the various tissues were determined.

2. (a) With the exception of the fluid component, there was a significant increase (P < 0.01) in the fresh weight of each tissue with both stage of gestation and level of feeding. At comparable litter sizes the total weight of the fetuses in late gestation was 16% higher with the higher feed intake. (b) The DM content of the individual uterine tissues increased significantly (P < 0.01) with increase in stage of gestation so that the mean DM content of the gravid uterus increased from 74.6g/kg at day 50 to 103.1 and 159, 0g/kg at days 90 and 110 of gestation respectively. (c) Neither stage of gestation nor feeding level influenced the respective energy contents of the individual uterine tissues, when expressed per g DM. The mean energy content of the total gravid uterus was 19.5 kJ/g DM. (d) The N content (g/g fresh weight) of the tissues increased with stage of gestation and was generally higher at the higher feeding level. The mean N contents (g/g DM) of the fetal, placental, fluid and empty uterine tissues were 0.090, 0, 101, 0.098 and 0.128 respectively.

3. The mammary tissue was the most variable of all the tissues investigated. Whereas the fresh weight and N content increased with stage of gestation, both the DM and energy content decreased.

4. Gompertz equations were fitted to describe the effects of stage of gestation, level of feed intake and litter size on the fresh weight and chemical content of the individual uterine tissues, total gravid uterus and mammary tissue. The use of these equations for calculating the nutrient requirements of pregnancy is demonstrated.

5. It was calculated that between days 50 and 110 of gestation the ME requirement for reproduction increased from 3 to 12% of maternal energy intake. The calculated requirement for protein was from 7 to 41 % of maternal dietary protein intake respectively.

1. The heat losses and energy and nitrogen balances of pregnant gilts, and of their non-pregnant litter sisters (controls), were measured for periods of 7 d at feed intakes of 1.8 or 2 3 kg/d (20 or 30 MJ metabolizable energy (ME) respectively) at an environmental temperature of 20°. The measurements were made within three separate periods of gestation; 40–60 d (early), 60–80 d (mid) and 90–110 d (late). Values for ME intake, heat loss, energy retention (ER), protein deposition and fat deposition were determined for both the pregnant and control animals on each treatment.

2. When expressed per kg body-Weight 0.75 per d, there was little difference in heat loss between pregnant and non-pregnant animals and between pregnant animals at the different stages of gestation at any given ME intake. However, heat loss was higher at the higher ME intake.

3. ER vaned inversely with heat loss. The decrease in ME intake (kJ/kg body-Weight 0.75 per d) during pregnancy resulted in a decrease in ER so that the pregnant animals were in negative energy balance at the low feed intake during late gestation. From the relation between ER and ME intake, estimates of the maintenance energy requirement (MEm) of 411 and 401 kJ/kg body-weight0.75 per d were calculated, with corresponding partial efficiencies of energy utilization (k) of 0.74 and 0.68 for the pregnant and non-pregnant animals respectively.

4. For the pregnant animals, protein deposition was highest during mid-pregnancy and was relatively independent of level of feeding during mid- and late pregnancy. There was little difference in protein deposition between pregnant and non-pregnant animals at the high feed intake. At the low feed intake, the pregnant animals generally had a higher protein deposition than their non-pregnant litter sisters and this was entirely associated with the accretion in reproductive tissue.

5. Fat deposition depended on the level of feeding, and at any given ME intake was similar for pregnant and control animals. In late gestation the low level of feeding was insufficient to prevent the pregnant animals losing fat. It was calculated that at term these animals lost 140 g fat/d from maternal stores.

6. From the relation between ME intake and protein and fat deposition, estimates of ME, and the energetic efficiencies of protein (k,) and fat (k,) deposition were determined. There was little difference in ME, (422 and 420 kJ/kg body-weight 0.5 per d) and k, (0.88 and 0.90) between pregnant and non-pregnant animals respectively. However, the pregnant animals had a higher k, (0.69 compared with 0.49 for controls) and this reflected the higher rates of protein deposition associated with pregnancy.

7. The efficiency of energy deposition in the reproductive tissue was calculated to be 0.72.

1. The stability of tryptophan was evaluated in several different food model systems using a chemical method (high pressure liquid chromatography after alkaline-hydrolysis) and rat assays. Losses of tryptophan were compared with the losses of lysine and methionine.

2. Whey proteins stored in the presence of oxidizing lipids showed large losses of lysine and extensive methionine oxidation but only minor losses of tryptophan as measured chemically. The observed decrease in bioavailable tryptophan was explained by a lower protein digestibility.

3. Casein treated with hydrogen peroxide to oxidize all methionine to methionine sulphoxide showed a 9% loss in bioavailable tryptophan.

4. When casein was reacted with caffeic acid at pH 7 in the presence of monophenol monooxygenase (tyrosinase; EC 1.14.18.l), no chemical loss of tryptophan occurred, although fluorodinitrobenzene-reactive lysine fell by 23%. Tryptophan bioavailability fell IS%, partly due to an 8% reduction in protein digestibility.

5. Alkali-treated casein (0.15 M-sodium hydroxide, 80°,4 h) did not support rat growth. Chemically-determined tryptophan, available tryptophan and true nitrogen digestibility fell 10, 46 and 23% respectively. Racemization of tryptophan was found to be 10% (D/(D+L)).

6. In whole-milk powder, which had undergone ‘early’ or ‘advanced’ Maillard reactions, tryptophan, determined chemically or in rat assays, was virtually unchanged. Extensive lysine losses occurred.

7. It was concluded that losses of tryptophan during food processing and storage are small and of only minor nutritional importance, especially when compared with much larger losses of lysine and the more extensive oxidation of methionine.

1. Tryptophan losses in stored milk powders and in different model systems representing the major reactions of food proteins during processing and storage were determined using four different chemical methods and in a rat assay.

2. Similar tryptophan values were obtained by the three chemical methods which included high pressure liquid chromatography (HPLC) after sodium hydroxide hydrolysis. colorimetric reaction with p-dimethylamino- benzaldehyde (p-DAB) after barium hydroxide hydrolysis, and fluorescence of the Norharman derivative after NaOH hydrolysis.

3. Tryptophan losses in the treated proteins as measured by the alkaline-hydrolysis methods were generally smaller than those determined by the rat assay. Good agreement however was obtained when the chemical value was multiplied by the true nitrogen digestibility.

4. Determination of tryptophan by reaction with p-DAB after papain (EC 3.4.22.2) digestion gave lower values in the processed proteins than the other chemical methods or the rat assay.

5. A method using alkaline-hydrolysis is recommended, preferably combined with HPLC-measurement of the liberated tryptophan.

1. Resting heat production, 18 h post-feeding, was studied in Hariana cattle (Bos indicus; Zebu) and in their F1 crosses with Jersey, Brown Swiss and Holstein Friesian, at 18.5° ambient temperature in a psychrometric chamber at different ages.

2. There was no significant change in the resting heat production on a per kg body-weight (W)0.75 per 24 h basis from 16–19 to 37–40 months of age in any of the genetic groups. The daily resting heat production, however, increased with increases in body-weight and age.

3. The resting heat production in all three F1 crosses was higher than that in Hariana cattle. Among the crosses, the resting heat production was highest in the Holstein Friesian x Hariana and lowest in the Jersey x Hariana.

4. Metabolizable energy (ME) intake per 24 h was significantly different between genetic groups and in different age groups. However, ME intake per kg W0.75 was not significantly different between genetic groups.

1. Twenty germ-free and twenty conventional male Fischer 344 rats, 3 months old, were fed ad lib. diets based either on normal or on amylomaize starch for 1 month. The absorption rate of sodium taurocholate. 25 mmol/l, was determined in vivo in jejunal or ileal segments. Each determination included five rats.

2. Jejunal absorption rate was not modified either by the amylomaize-based diet or by the digestive microflora.

3. Ileal absorption rate was slightly higher in germ-free than in conventional rats.

4. Ileal absorption rate was largely increased by the amylomaize-based diet. This increase was slightly larger in germ-free rats than in conventional rats.

5. It is suggested that dietary amylomaize starch has an action on the active absorption process of bile acid.

1. The vascular anatomy of the bovine omasal lamina permitted perfusion of a discrete area of the tissue. As occurs in vivo, oxygen was provided through the vascular system, while the luminal sides of the tissue could be kept in an anaerobic environment, thus allowing study of foregut tissue metabolism under physiologically realistic conditions.

2. O2 consumption of perfused leaves in the presence of anaerobic buffer was 64.9 and 73.5 nmol O2/mg dry weight per h in Expts 1 and 2 respectively, and was elevated (P < 0.05) when the lumen side of the tissue was exposed to an atmosphere of nitrogen gas.

3. In Expt 1, the rate of O2 consumption was increased (P < 0.01) by 35% as a result of suspension of a boiled preparation of rumen micro-organisms and particles (< 1 mm) in the anaerobic lumen buffer. Replacement of the boiled preparation with an unboiled suspension increased O2 consumption further by 11 %, but this was not statistically significant (P > 0.05).

4. In Expt 2, sequential addition of the following substrates or preparations to the lumen chambers all resulted in stepwise increases (P < 0.05) in O2 consumption; 8 mM-butyrate, boiled rumen micro-organisms and particles and, finally, unboiled rumen micro-organisms and particles.

5. Identities of the heat-labile and heat-stable components of the microbial and particle suspensions that caused enhancement of O2 removal across the perfused tissue are discussed.

1. Investigations were carried out on the feasibility of using an oral repletion technique in the rat to assess the bioavailability of copper in experimental sources providing no more than 250 μg Cu from any one source.

2. Preliminary studies on the response in plasma Cu ofpartially Cu-depleted rats given repletion doses of 20–50 μg Cu as CuSO4/d on four consecutive days indicated that this index of Cu status was insufficiently sensitive to Cu dose.

3. Incontrast, theactivityofcytochromecoxidase(EC 1. 9.3.1)in theduodenalmucosa ofpartiallycu-depleted rats showed a measurable and uniform response to 10 μg Cu as CuSO4/d given on three consecutive days. Furthermore, when the rats were given 0, 2.5, 5.0 or 10.0 μg Cu/d, the increase in cytochrome c oxidase activity above that of the unsupplemented control group was linearly related to Cu dose. The mean response in cytochrome c oxidase activity in groups of eight rats was therefore used to assess the availability of Cu from experimental sources relative to that of Cu as CuSO4, only 240 μg Cu being required from each experimental material.

4. The assay was used to study the effect of the Cu-antagonist molybdenum on the distribution of available Cu in digesta from sheep given dried grass either untreated (1.6 mg Mo/kg dry matter (DM)) or treated with ammonium molybdate (11.6 mg Mo/kg DM).

5. The relative availability of Cu in untreated dried grass (75%) was substantially higher than in rumen (12%), duodenal (43%) or ileal (28%) digesta. In all cases, addition of Mo to the diet resulted in a substantial reduction in Cu availability.

6. The effects of Mo on availabilitv of Cu are discussed with suecial reference to the Dossible involvement of thiomolybdates in the Cu-Mo antagonism.

1. Sixteen Friesian cows were used in Expt 1 to measure the effect of substituting urea-N with fishmeal-N either in early lactation (Part 1) or in mid-lactation (Part 2).

2. In Part 1 (days 15–84 of lactation) the major N constituent of the concentrate was urea (U), urea-N: fishmeal-N in the ratio 2:1 (UF) or 1:2 (FU), or fishmeal (F). In Part 2 (days 84–1 75 of lactation) only urea (UM) and fishmeal (FM) were used.

3. Replacement of urea-N with fishmeal-N significantly (P < 0.05) increased yield of milk protein both in early and in mid-lactation. At both stages of lactation the cows were, by calculation, in positive energy balance. In mid-lactation replacement of urea-N by fishmeal-N significantly depressed (P < 0.001) the concentration of fat in milk.

4. Blood urea concentration decreased with increasing fishmeal inclusion (P < 0.05) from U to FU.

5. In Expt 2 the diets used in Expt 1, Part 1, were offered at a maintenance level of feeding to non-pregnant, non-lactating heifers in a 4 x 4 Latin square design experiment. Digestibility of dry matter, organic matter and cell-wall constituents increased progressively (P < 0.05) with the first two increments of fishmeal inclusion.

6. A major effect of replacing urea-N with fishmeal-N was to increase digestible organic matter intake (DOMI) and differences in DOMI between treatments in Expt 1, Part 1, accounted for observed differences in performance.

1. When 103Ru-labelled Tris (1, 10-phenanthroline) ruthenium II chloride (103Ru-P) particulate marker in aqueous solution was added to the rumen of four steers given 5.5 kg grass hay/d at two-hourly intervals, the distribution of 103Ru-P marker among rumen particles of various sizes was the same at 4 h, 3 d and 7 d after administration, the concentration of 103Ru-P/g dry matter (DM) was inversely related to particle size and 0.30 of the 103Ru-P was associated with the DM of particles too large to be moved from the rumen at a meaningful rate. Thus, fractional outflow rate (FOR) of 103Ru-P would reflect, but was not a direct measure of, the FOR of the small particle pool in the rumen.

2. When rumen digesta were labelled with 103Ru-P, placed in nylon cloth bags and incubated in vitro with unlabelled digesta, 59% of the 103Ru-P disappeared from the nylon bag in 24 h, and 74% in 48 h. Similar results were obtained when large particles (retained by a 3.2 mm mesh screen during wet sieving) from rumen digesta were subjected to this procedure.

3. In a further experiment, the steers were given the hay in either the long or ground form and drinking water to which 10 g sodium chloride/l were, or were not, added.

4. The FOR of 51CrEDTA in centrifuged rumen fluid was increased (P < 0.05) from 1.78 to 2.10/d by grinding of the hay diet, but was not influenced by the intake of an additional 257 g NaCl/d. The FOR values of 103Ru-P in mixed rumen digesta and organic 35S in micro-organisms were linearly correlated (P < 0.05) and were not affected (P < 0.05) by grinding and salt treatments. On average, the FOR of organic 35S in micro-organisms was 0.41 of that of 51CrEDTA in centrifuged rumen fluid and 0.85 of that of 103Ru-P in rumen digesta respectively.

5. Grinding of the hay did not (P > 0.05) change the proportion of rumen DM (0.476–0.515) or faecal DM (0.107–0.153) retained by the 3.2 mm mesh and larger screens.

6. FOR from the rumen of a given size group of particles was calculated as the ratio, estimated daily flow from the rumen of the size group: rumen pool of the group. With increasing particle size there was a progressive decline in FOR; values of FOR for groups of particles greater than 4.0 mm were negligible. If the rumen DM was considered to behave as two pools, the 3.2 mm mesh screen appeared to be an appropriate division between the large-particle and the small-particle DM pools.

7. FOR of lignin present in mixed rumen digesta was 0.48 of the mean of the FOR values of the particle groups of the small-particle pool, while the FOR of lignin present in the small-particle pool was 0.92 of the mean small-particle FOR.

1. Groups of rats (n 8) were offered, to appetite, diets containing 10 (LP), 25 (MP) and 45 (HP)% of gross energy as protein energy from 45 d of age to slaughter 50 d later. At 53 d of age, half the rats on each diet were left at 22°while the other half were transferred to 6°. Water balances were measured daily, and digestibilities of energy and nitrogen and the metabolizability of the diets were measured for each rat over a 7 d period at some stage between the age of 74 and 95 d. The rats were slaughtered at day 95 and their carcasses were analysed for protein, lipid, energy and ash contents. Energy expenditure was calculated as the difference between metabolizable energy intake and energy retained.

2. Growth performance was best on the MP diet at both temperatures. At 22° the rate of gain of body-weight and of energy retention, although not of protein, were slightly reduced on the HP diet while overall performance was markedly inferior on the LP diet. At 6° the LP diet, while not so good as the MP diet, led to significantly better all-round growth performance than did the HP diet. Cold increased the energy expenditure of the rats by 50% (109–138 kJ/d); the increase was greater for the LP group than for the HP group.

3. Intrascapular brown adipose tissue hypertrophied in response to cold and to the LP diet.

4. Adrenal gland size was significantly increased by cold exposure and by increasing level of dietary protein concentration.

5. Urine volume was more closely related to the intake of protein than to that of energy. Urinary N concentration for the HP rats was approximately double that for those on the LP diet. Cold-exposed rats had a high water content in their fat-free carcasses, but there were no differences between the dietary treatments.

1. The relation between the level of food intake and gastrointestinal motility and digesta flow in the abomasum and small intestine was studied in sheep fitted with nichrome-wire electrodes in the gut wall, an abomasal and a duodenal catheter and a terminal ileal cannula.

2. Abomasal volume and outflow were calculated from CrEDTA dilution in six sheep and small intestinal transit time by the passage of Phenol Red in ten sheep.

3. The frequency of the migrating myoelectric complex of the small intestine was not altered by the level of food intake but the duration of the periods of irregular spiking activity, the amplitude of abomasal activity and the frequency of duodenal rushes were decreased as the level of food intake was decreased.

4. There was a linear relation between the level of food intake (FI) and abomasal outflow (mean with SEM: 327 (69) ml/h for each kg FI/d; P < 0.01), and abomasal volume (mean with SEM: 344 (50) ml/kg FI per d; P < 0.001), without any significant change in the half-time of marker dilution in the abomasum. Small intestinal transit time decreased with an increase in food intake (mean with SEM: - 54.9 (5.6) min/kg FI per d; P < 0.001).

5.It is concluded that abomasal volume and the rate of digesta flow from the abomasum and along the small intestine are linearly related to the level of food intake.

1. The effects of uncoupling of mitochondria1 oxidative phosphorylation on the efficiency of energy conservation during oxidation of amino acids, fatty acids, glycerol, glucose and 101 food proteins have been examined in order to compare how uncoupling at coupling site 1 affects energy yields compared with uncoupling at sites 2 + 3 and uncoupling by proton leakage. The effects of uncoupling by each mechanism on the isodynamic equivalents of carbohydrate, fat and protein at the level of cytoplasmic ATP yield have been estimated.

2. Energy conservation during amino acid oxidation decreases relative to that for glucose as uncoupling by all three mechanisms increases. This effect is least when uncoupling is at site 1 and is associated with a fall in the isodynamicequivalent for protein: glucose of 4%maximally, and a fall in the cytoplasmic ATP yield for glucose of 25% (15–30% when accounting for uncertainty in the choice of proton stoichiometries).

3. Variation in the efficiency of energy conservation for the different amino acids is large for both highly coupled and uncoupled mitochondria but the range of efficiencies for the oxidation of 101 food proteins is relatively small (less than 6% of the mean) for a tightly coupled system. This range increases absolutely (minimally fourfold) and relatively (minimally 44% of the mean value) with severely uncoupled mitochondria but is nearly constant (changes by less than 1% relative to the mean) within the probable physiologically relevant range of uncoupling in the whole body and in the full range of uncoupling at site 1. The rank order position of particular proteins within the range of values is found to change most for gelatin which is oxidized with least energy conservation in a severely (unphysiologically) uncoupled system and most efficiently in a fully coupled system when oxidation of protein is considered to be direct, i.e. not via gluconeogenesis.

4. For medium- and long-chain fatty acids, uncoupling at site 1 elevates the efficiency of energy conservation relative to that for glucose (maximally 4%) whereas uncoupling by other mechanisms decreases this relative efficiency. The pattern of effects for short-chain fatty acids resembles that for the amino acids.

5. The changes in the isodynamic equivalents of protein:glucose and of fat:glucose are small when uncoupling occurs at site I and tend to cancel for a mixed diet but are additive in the effect on food energy values when uncoupling is by the other mechanisms. Hence changes in the efficiency of oxidative energy coupling at site 1 in association with Luft's disease or dietary changes would result in effects which are of little true dietetic significance on the isodynamic equivalents of nutrients at the level of cytoplasmic ATP yield in vivo.