1. When fractionated by sodium dodecylsulphate-polyacrylamide gel electrophoresis (SDS-PAGE), strained rumen fluid from sheep fed on pelleted lucerne (Medicago sativa) hay showed no major protein components that stain with Coomassie Blue. This feature made it possible to monitor the fate of individual polypeptides within a protein mixture incubated in rumen fluid in vitro.

2. Extracts from a number of seed meals (sunflower (Helianthus annuus), lupin (Lupinus angustifolius), rape (Brassica napus) and pea (Pisum sativum L.)), as well as casein and bovine serum albumin, were examined in this system. The protein components of each seed type showed a wide range of resistances to degradation. One protein in pea seeds (pea albumin 1), which is particularly rich in cysteine, was almost as resistant to rumen degradation as bovine serum albumin.

3. Analysis of synthetic-fibre-bag experiments by SDS-PAGE showed that the rate of loss of total protein from solid meal residues does not provide an index of the resistance of individual protein components of the meal to rumen degradation. While there was no qualitative change in the protein profile of residual pea-seed meal inside a synthetic-fibre bag, there was considerable variation in the rate at which individual, solubilized protein components were degraded in the surrounding rumen fluid.

1. The effect of unsaturated long-chain non-esterified fatty acids (NEFA) on the human leucocyte sodium-pump was studied in vivo.

2. Plasma NEFA level was raised acutely from 0·28 (sd 0·10) to 2·54 (sd 0·48) mmol/l by infusion of ‘Intralipid 20%’ (trademark) at 90 ml/h with heparin, and the human leucocyte 22Na efflux rate constants were studied in eight normal weight males.

3. After 3 h, there was a significant lowering of the total (from 3·97 (sd 0·92) to 3·10 (sd 0·71)/h; P < 0·01) and ouabain-sensitive 22Na efflux rate constants (from 2·89 (sd 0·55) to 2·37 (sd 0·62)/h; P < 0·02). Ouabain-insensitive efflux rate constants showed a tendency to fall (from 1·08 (sd 0·51) to 0·73 (sd 0·23)/h). Leucocyte potassium content remained unchanged, but sodium content rose from 31 (sd 12) to 38 (sd 18) mmol/kg dry weight (P < 0·05). Total, ouabain-insensitive and ouabain-sensitive efflux rates did not change significantly during the Intralipid-heparin infusion.

4. Plasma insulin levels rose gradually throughout the 3 h infusion period.

5. In conclusion, NEFA, when raised to pathological levels, can inhibit the leucocyte Na-pump in vivo even in the presence of physiological levels of serum albumin, and may increase insulin secretion.

1. The present study was carried out to estimate precisely, via the nitrogen balance technique, the protein requirement of Nigerians (earlier estimated via the obligatory N method) using graded levels of protein intake.

2. Fifteen medical students of the University of Ibadan who volunteered to participate in the study were given graded levels of protein (0.3, 0.45, 0.6 and 0.75 g/kg body-weight per d) derived from foods similar to those usually consumed by the subjects.

3. Each subject was given each of the dietary protein levels for a period of 10 d. Subjects were divided into two groups and the feeding pattern followed a criss-cross design with one group starting with the highest level of protein intake (0.75 g) and the second group starting with the lowest level of protein intake (0.3 g). Mean energy intake during each of the eleven experimental periods was maintained at 0.2 MJ/kg per d. After an initial 5d adaptation period in each experimental period, 24 h urine and faecal samples were collected in marked containers for five consecutive days for N determination.

4. Mean N balance during consumption of the four protein levels (0.30, 0.45, 0.6 and 0.75 g/kg) were −11.02 (SD 8.07), −9.90 (SD 6.64), + 9.70 (SD 4.15) and + 5.13 (SD 4.62) respectively. Using regression analysis, the mean daily N requirement was estimated at 110.25 mg N/kg body-weight (0.69 g protein/kg body-weight). Estimates of allowances for individual variations to cover 97.5% of the population adjusted this value to 0.75 g protein/kg body-weight. Net protein utilization for the diet at maintenance level was estimated at 57.5.

1. Whole-body, hind-limb and uterine tissue metabolism of glucose was studied using a combination of isotopic and arterio-venous difference techniques in shorn and unshorn pregnant sheep over the final 4 weeks of pregnancy. This was combined with the measurement of the concentrations of oxygen and carbon dioxide in arterial blood and plasma concentrations of lactate, acetate, non-esterified fatty acids, 3-hydroxybutyrate, glycerol, growth hormone (GH), insulin, glucagon, cortisol, thyroxine and 3, 5, 3'-triiodothyronine (T3).

2. Glucose entry rate was 28 % higher in shorn ewes compared with unshorn controls, even though there was no difference in the arterial plasma concentration of glucose. This effect may have been caused by a decrease in the molar rate, insulin: glucagon (I:G), which was 40% lower in shorn ewes as a result of a significant decrease in the plasma concentration of insulin. There was no difference in the plasma concentration of cortisol or GH.

3. Blood flow across the hind-limb or uterine tissues was not significantly different between shorn and unshorn groups, neither were the net glucose uptake, glucose oxidation rate or contribution of glucose to O2 consumption across these tissues.

4. Insulin-tolerance tests performed on a separate group of shorn and unshorn ewes showed an increased sensitivity to the hypoglycaemic effects of insulin in the shorn group.

5. There was no significant difference between shorn and unshorn animals in the contribution of glucose to CO2 output or in the proportion of glucose entry rate oxidized. CO2 entry rate was 18% higher in shorn ewes compared with unshorn controls which resulted in a 26 % higher estimated value for heat production. There was a 47 % increase in glucose oxidation rate in shorn ewes but there was no significant difference in the proportion of total heat production which was derived from glucose. The arterial concentrations of O2 and CO2 were significantly higher in shorn ewes, which may be an indication of the higher metabolic rate in these animals. This effect may be mediated via a significant rise in plasma T3 concentration in the shorn group.

6. It is concluded that as a result of long-term cold exposure there is a significant increase in whole-body glucose entry and oxidation rates in the shorn pregnant ewe. The increase in insulin sensitivity at the same time as a decrease in plasma insulin concentration may represent a mechanism to ensure continued glucose supply to insulinsensitive tissues while the concomitant decrease in plasma I:G stimulates hepatic gluconeogenesis.

1. The effect of dietary methionine on the utilization of selenium from dietary selenomethionine ([Se]Met) for tissue Se deposition and for glutathione peroxidase (EC 1.11.1.9; GSH-Px) synthesis was studied in male weanling rats.

2. When rats were given 0.5 mg Se as [Se]Met/kg diet supplemented with 0, 4 or 9 g methionine/kg, Se in plasma, erythrocytes, liver and muscle increased significantly over the 20 d period for all methionine-treatment groups. The increases in erythrocyte and muscle Se, however, were significantly higher in rats fed on the methionine-deficient diet compared with the methionine-supplemented diets.

3. In contrast to the increases in tissue Se, GSH-Px activity in liver, plasma and muscle decreased in methionine-deficient rats given 0.5 mg Se as [Se]Met/kg whereas GSH-Px activity was maintained or increased in rats supplemented with methionine.

4. The percentage of tissue Se associated with GSH-Px was calculated from the measured Se concentration and GSH-Px activity. A significantly lower percentage of Se was associated with GSH-Px in methionine-deficient rats compared with methionine-supplemented rats.

5. These results show that Se from dietary [Se]Met is preferentially incorporated into body proteins rather than used for GSH-Px synthesis when methionine is limiting in the diet.

6. These results further suggest that [Se]Met might not be the optimum Se compound to use for Se supplementation because metabolism of dietary [Se]Met to a biochemically active form, such as GSH-Px, was impaired when [Se]Met was provided in diets low in methionine.

1. The present paper reports the effects of dietary modifications on the diurnal pattern of concentrations of certain metabolites and hormones in the peripheral blood of lactating dairy cows. The cows were given fixed rations of hay and high-cereal concentrates in the proportions of 30:70 or 10:90 (w/w). The concentrates were given in either two or six equal meals daily; the hay was given twice daily.

2. Previous reports of the same experiment had shown that milk-fat yield and concentration were reduced by increasing the proportion of concentrates in the diet and increased by more frequent feeding of the concentrates. These changes could be explained in part by changes in rumen volatile fatty acid (VFA) proportions and mean daily concentrations of VFA, particularly propionic acid, and insulin in the peripheral blood, but these factors failed to explain all the increase in milk-fat concentration caused by more frequent feeding.

3. Analysis of blood samples taken at hourly intervals for 24 h at two stages of lactation showed that, in the cows fed six times daily, the concentrations of metabolites and hormones remained relatively constant over the day. In the cows fed twice daily, the concentrations of VFA, 3-hydroxybutyric acid and insulin all increased after both meals whereas the concentrations of glucose and growth hormone tended to fall. The concentration of non-esterified fatty acids tended to increase overnight and fall rapidly after the morning feed. The concentrations of glucagon, thyroxine and prolactin showed no clear pattern in relation to meals. The postprandial responses of propionate, insulin and growth hormone were greater with the higher concentrate diet.

4. The maximum concentration and the diurnal range of concentrations were reduced by more frequent feeding of both diets in the case of propionic acid and of the higher concentrate diet in the case of insulin, but the effects on insulin concentrations of more frequent feeding of the lower concentrate diet were smaller and not significant. The maximum concentration and the diurnal range of concentrations of growth hormone were unaffected by meal frequency.

5. It is concluded that the severity of milk-fat depression in cows fed twice daily is increased by the rapid rise in propionic acid concentration in the peripheral blood after a meal, which in turn increases insulin secretion and may be accompanied by a suppression of growth hormone release. This causes lipogenesis to be diverted towards adipose tissue at the expense of the mammary gland. In cows fed more frequently, VFA absorption is more evenly spread over the day and is not closely associated with changes in insulin or growth hormone concentrations.

1. A continuous 40 d metabolic nitrogen balance study was conducted on twelve young men aged 25 (sd 2.6) years to evaluate the adequacy of a previously determined safe level of protein intake.

2. Subjects were fed on diets which they were habitually accustomed to and which provided a protein level of 0.75 g protein (N × 6.25)/kg body-weight per d as the safe level and an energy intake level of 0.2 MJ/kg body-weight per d. N balances, including an estimate for integumental losses as well as certain biochemical variables, were determined for the last 5 d of two consecutive 20 d diet periods.

3. Only two of the twelve subjects were observed to be in negative N balance during the final 5 d of the 40 d period. N balance was generally positive at 8.24 (sd 8.61) mg N/kg body-weight, thus confirming the adequacy of 0.75 g protein/kg body-weight per d as a safe level of protein intake in the majority of the subjects.

1. The relation between bacterial degradation of three viscous polysaccharides (guar gum, ispaghula and xanthan gum) by colonic bacteria in vitro and their effects on colonic function were investigated by comparing the results of anaerobic in vitro incubations with fresh faeces from seven healthy volunteers (measuring viscosity, pH and gas production) with the effects of feeding all three polysaccharides to the same volunteers for 1 week each (14–15 g/d) on faecal mass and whole-gut transit time.

2. Guar gum was rapidly fermented in vitro by faecal bacteria from all volunteers with concomitant loss of viscosity, reduction in pH and generation of gases. Ispaghula maintained its viscosity during incubation, but the pH fell significantly. The results of xanthan gum incubations showed considerable individual variation.

3. Only ispaghula significantly increased faecal mass, whilst none of the gums significantly affected stool frequency or transit time. Statistical analysis of the pooled results showed that although transit time and faecal output were inversely related, feeding viscous polysaccharides could influence these indices independently. Stool frequency was significantly correlated with the transit time, but not the faecal output.

4. Transit time was reduced by gum feeding to a significantly greater extent in those subjects whose faecal bacteria reduced or removed the viscosity of that gum, than in those subjects where the viscosity was maintained. In contrast, there was a smaller increase in faecal mass when the viscosity of the appropriate cultures was removed than when it was maintained or reduced. Increases in stool frequency were significantly associated with hydrogen production from in vitro cultures.

1. Of the nineteen plants screened, six were found to contain large quantities of condensed tannins. Black locust (Robinia pseudo-Acacia), bush clover (Lespedeza bicolor), wistaria (Wistaria floribunda) and Japanese knotgrass (Reynoutria japonica) were used for the present experiment. Tannins of the investigated plants were fractionated into three or four molecular forms, according to the degree of polymerization, by chromatography on a column of Sephadex LH-20.

2. The protein-precipitating capacity of the fractionated tannins increased with the increase in degree of polymerization. The inhibitory effect of tannins on trypsin (EC 3.4.21.4), a-amylase (EC 3.2.1.1) and lipase (EC 3.1.1.3) activities in vitro also increased with the increase in degree of polymerization. The digestion of tannin-bovine serum albumin complex by trypsin was related to the degree of polymerization of tannins complexed.

3. Inclusion of black locust tannins in the diet (10 g/kg) depressed the activities of trypsin and α-amylase in the upper, middle and lower parts of the intestine of the rats, but the lipase activity was increased in the middle part and remained unaffected in the upper and lower parts. It is presumed that the tannins have little affinity for lipase.

4. Digestion trials, when the microflora level of the alimentary canal of rats was reduced by dietary antibiotic treatment, revealed that the inclusion of tannins in the diet (20 g/kg) depressed the digestibilities of proximate constituents, except crude fat, and increased faecal bile acid excretion.

1. To study the efficiency of rehabilitation after different periods of protein–energy malnutrition, we used as a model preweaning malnourished rats. After weaning, male Wistar rats were fed on a protein-deficient diet (50 g casein/kg) ad lib. for the whole study (DR group) or rehabilitated with normal diet (180 g casein/kg; RR group) from weaning, week 0, or weeks 1, 3, 5, 8 and 16 thereafter.

2. Twelve animals from the DR group were killed at the beginning of each rehabilitation period. The twelve rehabilitated rats were killed after 2 weeks. Body-weight and epididymal adipose tissue weight, blood glucose, plasma immunoreactive insulin (IRI) and immunoreactive glucagon (IRG), and pancreatic contents of IRI and IRG were determined.

3. Food intake of RR rats rose significantly except during the last period where body-weight increased less than that during the previous periods. Fat-pad weights increased in the same manner in DR and RR groups.

4. Blood glucose fell and plasma IRG rose significantly without any change in plasma IRI after each rehabilitation period, except during the last period where blood glucose concentrations became stable. Pancreatic IRG and IRI showed the same type of response to those of the plasma.

5. All short-term rehabilitation periods were similarly efficient at producing catch-up growth. High insulin sensitivity of target cells was responsible for good recovery except after long-term malnutrition.

1. The effect of maternal iron deficiency on milk composition and consumption by sucking rats was investigated.

2. Dams (n 42) were fed on semi-purified diets with either 8 (Fe-) or 250 (Fe+) mg Fe as ferrous sulphate/kg throughout gestation and lactation. Total milk intake was determined at days 7, 12 and 17 of lactation from the rate of disappearance of 3H2O from the total body water pool of pups. Measurements of milk constituents and Fe status of animals also were made.

3. Feeding the Fe- diet led to the development of anaemia in dams and pups and to growth retardation of sucking pups.

4. Concentrations of total lipid and Fe in milk from Fe- dams were significantly lower than those from Fe + dams. Mean milk intakes (ml/d) of Fe-deficient pups were 21 and 28% less than intakes of Fe-sufficient pups on days 12 and 17 respectively. However, when expressed per kg body-weight, mean milk intakes were similar between groups on days 17 and 12 and increased by 47% in the Fe-deficient group on day 17 of lactation.

5. It is concluded that maternal Fe deficiency affects the quality of milk ingested by neonatal rats. However, Fe-deficient pups are at least partially able to compensate for reduced milk energy and nutrient contents by increasing intake in late lactation.

1. Protein fractional synthesis rate (FSR) was measured in some major tissues and in the whole body of six 1-week-old sucking lambs by a large injection of L-[3H]valine.

2. Upper estimates of tissue protein FSR (%/d), assuming that the tissue-homogenate free-valine specific radioactivity defined that of valyl tRNA, were 115.0 in liver, 24.1 in skin, 22.9 in the white M. tensor fasciae latae, 21.6 in the red M. diaphragma and 19–6 in the remainder (exsanguinated whole body without liver and gastrointestinal tract) of lambs.

3. Absolute synthesis rates (ASR) of tissue protein were 17, 19 and 42 g/d in the liver, skin and skeletal muscle respectively, and 112 g/d in the remainder. The ASR of whole-body protein, derived from the tissue values, was 146 g/d, i.e. 33 g/d per kg body-weight. The calculated whole-body protein FSR was 23.9 %/d.

4. The relative percentage contribution of liver, skin and skeletal muscle to whole-body protein synthesis was 11.7, 13.1, and 29.0.

5. We concluded that tissue protein FSR in lambs were in exactly the same decreasing order, from visceral tissues to skeletal muscles, as observed in rats. The ovine FSR estimates and the partitioning of protein synthesis between tissues were in the same range as values recently obtained by flooding-dose experiments in immature rats, piglets, and even in chicks. These findings suggest that inter-species differences are rather limited.

1. The objective of the present experiment was to study the effects of oak (Quercus incana) leaves rich in tannins on various enzyme activities of the bovine rumen.

2. The procedure employed was incubation of tannin-rich, very-low-tannin or virtually tannin-free leaves in nylon-gauze bags in the rumen, and determination of enzyme activities in microbes tightly bound to the solid matrix and in microbes loosely plus tightly attached to the solid matrix.

3. The activities of urease (EC 3.5.1.5), carboxymethylcellulase, glutamate dehydrogenase (EC 1.4.1.2) and alanine aminotransferase (glutamic-pyruvic transaminase) (EC 2.6.1.2) were significantly lower in the tannin-rich group, whereas the activities of glutamate ammonia ligase (glutamine synthetase) (EC 6.3.1.2; both yγ- glutamyltransferase (EC 2.3.2.2) and the forward reaction) were higher in the tannin-rich group. These changes were more marked in micro-organisms tightly bound to the solid matrix than in the more complex microbial compartment.

4. The protein, DNA and RNA contents, and protein: RNA ratio, were significantly lower in the tannin-rich group, whereas no difference was observed for protein: DNA between the groups.

5. Effects of tannin-containing extracts of oak leaves on various rumen enzymes in vitro showed a trend similar to that observed in nylon-gauze bags, suggesting that the changes observed in various compartments were due to the tannins of oak leaves.

1. Male Sprague-Dawley rats weighing 146·5 (se 4·3)g were fed on a semi-synthetic diet containing 0, 25 or 150 mg cimaterol/kg for 12 d. Net changes in weight and composition of carcass, liver, heart, gastrointestinal tract, gastrocnemius plus plantaris muscles, skin and remainder were estimated by comparative slaughter.

2. Cimaterol increased protein gains in gastrocnemius plus plantaris muscles from 0·09 g in controls to 0·14 and 0·12 g in 25 and 150 mg cimaterol/kg groups respectively. Carcass protein gains increased from 6·27 g in controls to 8·00 and 7·05 g in 25 and 150 mg cimaterol/kg groups respectively.

3. Rats treated with cimaterol either gained less fat or actually lost fat from all tissues studied, whilst control rats gained fat. These changes were reflected in lower energy retention in cimaterol-fed rats.

4. Energy intake was not affected by treatment. Cimaterol increased heat production from 776 kJ/kg body-weight0·75 in controls to 863 kJ/kg body-weight0·75 in both treated groups. Gross efficiency was reduced from 17·4% in controls to 8·0 and 7·7% in rats fed on 25 and 150 mg cimaterol/kg diets respectively.

5. These results indicate that cimaterol increases protein gain at the expense of fat in rats. In addition, subcutaneous adipose tissue appears to be more sensitive than abdominal fat, whilst protein gains are particularly enhanced in skeletal muscle relative to other body tissues.

1. Guinea-pig dams were fed on purified diets containing high (5 g/kg diet plus 1 g/l drinking water) or moderate (0.5 g/kg diet) levels of ascorbic acid, in combination with high (1 g/kg diet) or moderate (0.043 g/kg diet) levels of iron, during pregnancy and suckling. Their offsprings' diets contained 0.1 g ascorbic acid/kg and 0.04 g Fe/kg.

2. High ascorbic acid intake clearly enhanced both tissue ascorbate and Fe storage in the dams, and high Fe intake increased both the dams' and the pups' tissue Fe stores.

3. In the animals receiving high Fe intake, a co-existing high ascorbate intake by the dams reduced the growth rate of the offspring, but only during the early stages of development, not during the later stages of post-weaning growth. All the pups' tissue ascorbate levels fell after weaning, but those born of the dams receiving the high ascorbic acid diets did not fall to levels lower than those of the other pups.

4. Thus, although certain disadvantages to the offspring resulting from very-high ascorbic acid intake by pregnant guinea-pig dams were detected, these did not include permanently increased ascorbate requirements, and hence a progression to scurvy as the pups grew and matured.

1. A primary growth of perennial ryegrass (Lolium perenne) was cut early or late to produce silages of high and low digestibility. The crops were wilted for 2–4 h and preserved with formic acid at 2.4 litres/t fresh weight. The resulting silages were well preserved with a pH of 3.9 and 3.8, lactic acid content of 108 and 73 g/kg dry matter (DM) and total nitrogen content of 24.6 and 18.4 g/kg DM for early- and late-cut silage respectively.

2. Forty-two British Friesian male castrates (steers) initially 12 months of age and 305 kg live weight (LW) were used, of which ten were slaughtered at the start of the experiment. The remaining steers were divided into four groups of eight animals and were given the early-cut silage alone (H) or the late-cut silage alone (L) or with barley at either 280 (LCI) or 560 (LC2) g DM/kg total DM. The intake of total DM was restricted to a daily allowance of 18 g DM/kg LW and the steers were slaughtered in two groups after 119 and 140 d on experiment.

3. Both earlier cutting of herbage and substitution of late-cut silage with barley significantly (P <0.001) increased the apparent digestibility of gross energy (H0.748, L0.619, LC10.668, LC20.705), whereas earlier cutting increased the digestibility of acid-detergent fibre from 0.638 (L) to 0.777 (H) and substitution with barley resulted in a significant (P <0.001) depression to 0.595 (LCI) and 0.519 (LC2). Substitution of late-cut silage with barley significantly (P <0.001) increased metabolizable energy (ME) intake from 58.9 (L) to 69.5 MJ/d (LC2) and crude protein (N × 6.25; CP) intake from 688 (L) to 779 g/d (LC2), but the highest intakes of ME and CP (73.5 MJ/d and 952 g/d respectively) were achieved with the early-cut silage.

4. Earlier cutting resulted in significant (P <0.001) increases in body-weight gain from 292 to 696 g/d, fat gain from 121 to 260 g/d, protein gain from 31.1 to 86.9 g/d and energy retention from 5.5 to 12.2 MJ/d for silages L and H respectively. However, substitution of the late-cut silage with barley increased gains to a greater extent. Thus, empty-body gain was increased to 552 and 800 g/d, fat gain to 189 and 302 g/d, protein gain to 76 and 116 g/d and energy retention to 9.2 and 14.6 MJ/d for diets LCI and LC2 respectively. The difference in gains between diets H and LC2 achieved significance (P <0.05) for all components except fat.

5. It is concluded that although earlier cutting of herbage for silage results in increased gains of protein and energy, the amounts retained are less than those from a similar increment of ME and CP achieved by substituting a late-cut silage with barley.

1. The effect of harvesting date of perennial ryegrass (Lolium perenne) on the nutritive value of the resultant silage and the effect of substitution of late-cut silage with barley was examined in growing cattle. The diets comprised early-cut (H) and late-cut (L) silage offered alone or with 280 (LCI) or 560 (LC2) g rolled barley/kg total dry matter (DM) substituted for late-cut silage.

2. Both silages were prepared with the addition of formic acid (850 g/l; 2.4 litres/t fresh weight) to a partially wilted crop, and were judged to be well fermented (pH 3.9, 3.8) with lactic acid contents of 108 and 73 g/kg DM, total nitrogen contents of 24.6 and 18.4 g/kg DM and ammonia-N contents of 121 and 124 g/kg total N (values for early- and late-cut silages respectively).

3. Two experiments were conducted to measure duodenal non-NH3-N (NAN) supply in relation to N intake on the four diets (feeding level 18 g DM/kg live weight (LW)) and to examine the partition of the metabolizable energy (ME) supply from the four diets using open-circuit indirect calorimetry (three feeding levels, 14, 17 and 20 g DM/kg LW). The experiments were undertaken with eight and nine Friesian male castrates respectively with a mean starting weight of 300 kg and age 12 months. The animals used in Expt 1 had been previously fitted with cannulas into the dorsal rumen and the proximal duodenum.

4. NAN supply was significantly higher on diet H than all other diets which were similar irrespective of the level of barley inclusion. Mean ME contents (MJ/kg DM) of the two silages differed markedly (H 11.9, L 9.7) and barley addition (LCI and LC2) restored values to 10.7 and 11.1 MJ/kg DM respectively. Estimated NAN absorption in relation to energy supply was significantly higher for diet H (1.47 g/MJ ME) than for all other diets (mean 1.25 g/MJ ME).

5. Partition of ME supply using conventional linear analysis indicated dietary differences with respect to estimated ME for maintenance (L > H, LCI and LC2) and efficiency of utilization of ME supplied above maintenance (L > H, LCI and LC2), but difficulties in biological interpretation of these findings led to the use of exponential curve analysis. This provided an improved description of the findings, and whilst dietary differences were apparent, none were statistically significant. It was concluded that a single exponential equation could be used satisfactorily to describe all values.

6. The consequence of these findings in relation to the carcass retentions of energy. fat and protein reported by Thomas et al. (1988) is discussed and possible reasons for the discrepancies in energy retention measured by comparative slaughter balance and open-circuit indirect calorimetry are considered.

1. Concentrations of amino-nitrogen, glucose, reducing sugars and lactic acid in blood obtained from arterial and portal permanent catheters were measured together with the portal hepatic blood flow-rate during a post-prandial period of 8 h in twenty unanaesthetized pigs (initial mean body-weight 52·3 (SEM 0·9) kg) receiving experimental meals (200–1000 g) at 3–4 d intervals from 6–8 to 20 d after surgical implantation of the catheters and electromagnetic flow probe. The semi-synthetic starch-based diets contained variable amounts of fish meal giving crude protein (nitrogen x 6·25; CP) concentrations (g CP/kg) of 80 (seven meals), 120 (twenty-two meals), 160 (six meals) and 240 (nine meals).

2. After the meal the concentration of amino-N increased with increasing levels of protein intake and increased more in the portal than in the arterial blood. There were significant relations between amounts of amino-N appearing in the portal blood at various time-intervals after the meal and the level of protein intake. Values for the ratio, amount absorbed within 8 h: amount ingested (absorption coefficient: 0·633 for a mean intake of 13·4 g N) decreased with increasing level of protein intake.

3. There was a rise in glycaemia after the meal, increasing with the amount of carbohydrate eaten, and this was more marked in the portal than in the arterial blood. There were also significant relations between amounts of glucose absorbed and amounts of starch ingested. However, the appearance of glucose in the portal blood was less marked than that of amino-N since the absorption coefficient within 8 h was lower (0·504 for a mean intake of 291 g reducing sugars). This was most probably due to a larger uptake of glucose by the intestinal cell wall.

4. Amounts of lactic acid appearing in the portal vein during the post-prandial period did not depend on amounts ingested; they ranged from 3 to 1·6 g/h from the 1st to the 8th hour after the meal.

1. Male, 4–5-week-old, genetically diabetic mice (C57BL/KsJ db/db) and non-diabetic heterozygote litter-mates (C57BL/KsJ db/+)were fed on a diet containing 1 mg zinc/kg (low-Zn groups) or 54 mg Zn/kg (control groups) for 27 d. Food intakes and body-weight gain were recorded regularly. On day 28, after an overnight fast, animals were killed and blood glucose and insulin concentrations, liver glycogen, and femur and pancreatic Zn concentrations were determined.

2. The consumption of the low-Zn diet had only a minimal effect on the Zn status of the mice as indicated by growth rate, food intake and femur and pancreatic Zn concentrations. In fact, diabetic mice fed on the low-Zn diet had a higher total food intake than those fed on the control diet. The low-Zn diabetic mice had higher fasting blood glucose and liver glycogen levels than their control counterparts. Fasting blood insulin concentration was unaffected by dietary regimen.

3. A second experiment was performed in which the rate of loss of 65Zn, injected subcutaneously, was measured by whole-body counting in the two mouse genotypes over a 28 d period, from 4 to 5 weeks of age. The influence of feeding low-Zn or control diets was also examined. At the end of the study femur and pancreatic Zn and non-fasting blood glucose levels were determined.

4. All mice fed on the low-Zn diet showed a marked reduction in whole-body 65Zn loss compared with those animals fed on the control diet. In the low-Zn groups, the loss of 65Zn from the diabetic mice was significantly greater than that from heterozygote mice. This difference was not observed in the control groups. Blood glucose levels were elevated in the low-Zn groups. Possible reasons for these observations are discussed.

5. The present study demonstrates an adverse effect of reduced dietary Zn intake on glucose utilization in the genetically diabetic mouse, which occurred before any significant tissue Zn depletion became apparent.

1. The influence of the protein content of the diet on glucose homeostasis was studied in the rat. Rats of 28 d of age received ad lib. a control diet containing (g/kg) 150 protein (P15), or a diet containing 50 protein (P5) or 450 protein (P45). Since P5 rats spontaneously reduced their food intake, a fourth group of rats (P25) received the same amount of energy as P5 rats and the same amount of protein as P15 rats.

2. After 12–13 weeks on these diets, plasma glucose and insulin levels were similar in fed P45, P25 and control P15 rats, but were lower in P5 rats. In fasted animals, plasma glucose and insulin levels were also decreased in P5 rats, whereas plasma glucose levels were increased in both P45 and P25 animals.

3. During an oral glucose tolerance test, the glucose rise was only slightly larger in P5 than in P15 rats in spite of a considerably smaller increase in insulin levels. P45 rats displayed a normal tolerance to glucose with a normal insulin response, whereas tolerance to glucose was slightly poorer in P25 rats in spite of a normal insulin response.

4. Pancreatic insulin stores were lower in P5 than in control P15 rats, not only because of the smaller size of their pancreas, but also because of a decrease in the insulin concentration in the gland. A much smaller decrease was also observed in P25 rats, whereas insulin reserves were not altered in P45 rats.

5. It is concluded that the changes in glucose homeostasis observed in protein-energy malnutrition (P5 rats) are due to protein deprivation rather than to energy deprivation. A high-protein diet has little influence on glucose homeostasis in the rat.