1. Complete 24 h energy and nitrogen balances were measured for fifteen subjects at three levels of energy intake and for two other subjects at two levels of intake.

2. At each level, the fifteen subjects ate diets consisting of fifteen to twenty separate foods for 7 or 8 d. Faeces and urine were collected for the final 4 d. Respiratory gas exchange was measured during the final 72 h while the subjects stayed in an 11 m3 open-circuit respiration chamber, and simulated office or light household work. The energy balance of the other two subjects was determined initially in a similar way when they consumed a diet which was sufficient for energy equilibrium. Subsequently, the measurements were repeated twice at the same high level of metabolizable energy (ME) intake after 4 and 18 d on that diet.

3. Neither energy nor N digestibilities were significantly affected by intake level or subject. Due to relatively small urinary energy losses the ME content of the gross energy increased slightly at the higher intake.

4. Respiratory quotient increased with intake level from 0.78 to 0.87.

5. The efficiencies of utilization of ME were approximately 1.0 for maintenance (from the low to the intermediate intake level) and decreased to about 0.9 for maintenance and energy deposition (from the intermediate to the high intake level).

6. Estimates of daily ME requirements at energy equilibrium were 149 (SD 13) kJ ME/kg body-weight, 432 (SD 33) kJ ME/kg body-weight0.75 and 204 (SD 22) kJ/kg lean body mass. The former two values were negatively correlated with percentage body fat although not significantly so.

7. ME utilization and heat production of the other two subjects were nearly equal after 6 and 20 d on a diet supplying 1.5–1.7 times the ME needed for energy equilibrium.

1. A 45 d metabolic study was carried out in four young adult male North American residents consuming a controlled diet based on an amino acid mixture. During the initial 10 d, total daily selenium intake was adjusted to 107.7 (SE 0.1) μg/d, which was reduced to 11.4 (SE 0.1) μg/d for the remaining 35 d.

2. Two doses of a stable isotope (74SeO32-) were administered orally in the post-absorptive state on days 4 and 39 of the study.

3. Se balance (faecal + urinary excretion) as well as stable isotope excretion studies were carried out for the entire 45 d period; blood plasma and erythrocyte Se concentrations were also monitored.

4. Plasma Se concentrations (μg/ml) fell progressively from the initial value of 0.132 (SE 0.007) to 0.083 (SE 0.008) at the end of the study. The erythrocyte concentrations of Se did not vary in a consistent manner (average value for the entire study 0.147 (SE 0.002) μg/ml).

5. Faecal excretion of unenriched Se decreased from 66 (SE 6) μg/d for days 1–10 to 10.2 (SE 0.8) μg/d for days 14–40. Mean urinary excretions of the unenriched Se were 43.9 (SE 2.8) μg/d (days 1–10) and 26.9 (SE 4.6) μg/d (days 14–40). Total balance (intake - faecal excretion - urinary excretion) for unenriched Se was μg/d):-18 (SE 7) days 10–19, -17 (SE 2) days 19–39, -5 (SE 1) days 38–45.

6. Fractional absorption of the ingested label was 0.529 (SE 0.032) and 0.542 (SE 0.038) for the Se-adequate and Se-restricted phases of the study. However, urinary excretion of the absorbed label was reduced from 6.57 (SE 0.73)% for day 1 of the Se-adequate phase to only 3.32 (SE 0.26)% for day 1 of the Se-restricted phase. Similar observations were also made for day 7 of each phase.

7. These findings indicate that immediate contribution of ingested Se to the urinary Se pool is small.

1. The dietary intake of pregnant Asian women (that is originating from the Indian subcontinent) attending Sorrento Maternity Hospital in Birmingham was determined, using the weighed and recall techniques, at five-weekly intervals from 18 to 38 weeks of pregnancy.

2. Mean energy intake of the group was 7.1 MJ (1700 kcal)/d. The intakes of most nutrients were substantially below those consumed by pregnant European women in Britain, a little below those of expectant Pakistani mothers in Islamabad, and about the same as those of expectant East London mothers. Intakes of vitamin D, total folate, vitamin B6, zinc and magnesium were particularly low.

3. These observations suggest that a number of Asian women in Birmingham are likely to experience nutritional stress in pregnancy, and there is some anthropometric and biochemical evidence from Sorrento, published elsewhere (Bissenden et al. 1981), to support this.

4. A possibly beneficial feature of the diet was a low sodium intake (2 g/d). Previous work at this hospital has noted a lower prevalence of hypertension in pregnant Asian women (Wharton et al. 1980; Bissenden et al. 1981).

1. The previous paper (Eaton et al. 1984) described the nutrient intake of pregnant Asian women attending Sorrento Maternity Hospital, Birmingham using the weighed and recall methods. The present paper describes the subethnic variation in nutrient intake by comparing the results from Pakistanis, Sikhs, Hindus and Bangladeshis and also describes food eaten by the pregnant women.

2. Generally. Sikhs had the highest intake of most nutrients (mean energy 7.5 MJ (1800 kcal)/d) and the greatest variety of foods; they ate chapatti and paratha but few ate meat. Hindus had a very similar diet but more ate meat, chicken and rice. Pakistanis had an energy intake about 10% below that of the Sikhs and Hindus; meat was eaten, and intake of fruit, and therefore vitamin C, was quite large. Bangladeshis were the smallest women; they had the lowest intake of energy (mean energy 6.5 MJ (1555 kcal)/d) and most nutrients, except for protein, so that 15% of energy was provided by protein. Fish, rice and a low-fat intake were other features of their diet.

3. From a nutritional standpoint, peoples coming from the Asian subcontinent should be divided into subethnic groups; the collective term ‘Asian’ is insufficient.

4. It is not clear whether these differences have any effect on the life and health of the individuals. Comparison of groups does not suggest an obvious relationship between dietary intake and fetal growth; however, there is other evidence to implicate the possible role of deficiencies of protein, energy, zinc and pyridoxine.

5. The results provide some support for the community nutritional policies of (a) offering vitamin D supplements to all pregnant Asian women and (b) fortifying bread with calcium, thiamin and nicotinic acid. There is probably no need to offer vitamin A and C supplements but they are harmless. Indications for iron supplementation are no different from those for white English women.

1. Male Wistar rats (approximately 200 g) were given fibre-free semi-synthetic diets containing either sucrose (S) or a sucrose-starch mixture (SS) as the carbohydrate component, or a diet similar to SS containing 40 g guar gum/kg (G), or 100 g cellulose/kg (C). The animals remained healthy, and weight gain after 30 d was similar in all groups.

2. The small intestines of the animals given diet G were significantly longer than those of the other groups, and showed signs of increased mitotic activity and mucosal growth.

3. No significant differences in mucosal enzyme activity were detected between the two fibre-free control groups. Lactase (EC 3.2.1.23) and alkaline phosphatase (EC 3.1.3.1) activities were significantly lower than controls in group G, but were higher in group C.

4. Kinetic analysis of 3-O-methyl glucose uptake by isolated intestine indicated that the maximum transport rate (Vmax) of tissue from group G tended to be lower than from the fibre-free group SS and group C.

5. It is concluded that materials which are classed as dietary fibre but which differ markedly in their physical properties may also differ in the functional changes to which they give rise in the small intestine. These changes may be at least partially mediated by effects on mucosal cell proliferation.

1. Four pigs initially of 30 kg live weight were surgically prepared with two re-entrant cannulas in the jejunum 1.0 m apart which allowed an isolated loop to be formed through which solutions were perfused. 51Cr-EDTA was used as a marker for measuring net secretion or absorption.

2. A new Ringer solution was made, the ionic content of which resembled more closely that found in the jejunum of pigs given similar diets, than Krebs-Ringer solution.

3. The absorption of glucose and water from Krebs-Ringer and new Ringer solutions was compared.

4. The effect of guar gum on the absorption of glucose and water from solutions of glucose and maltose was studied.

5. There was a trend (not significant) for greater absorption of glucose and water from the new Ringer solution than from the Κ rebs-Ringer solution.

6. Guar gum significantly reduced the net absorption of glucose from glucose or maltose solutions from 74.2 to 41.4% (P < 0.001) and 71.1 to 35.0% (P < 0.001) respectively.

7. Guar gum significantly reduced the net absorption of water from the glucose solution from 42.7 to 8.3% (P < 0.01) and from the maltose solution from 49.2 to 5.1% (P < 0.001).

8. The lack of differences between the absorption of glucose from solutions of glucose or maltose suggested that maltase (EC 3.2.1.20) activity was not inhibited to the extent that this limited the rate of glucose absorption.

1. Four pigs, initially of 30 kg live weight, were surgically prepared with two re-entrant cannulas in the jejunum, 1.0 m apart. This allowed an isolated loop to be formed through which Ringer solutions were continuously perfused for 6.5-h periods per day.

2. The effects of two Ringer solutions of contrasting composition on nitrogen secretion were measured in a preliminary study.

3. The effects of guar gum (6.7 g/l) on N secretion during perfusions of solutions of glucose or of maltose (20 g/l) were measured.

4. N secretion did not differ significantly between the two Ringer solutions.

5. Addition of guar gum to the solution of glucose increased mean N secretion from 69.2 to 133.9 mg/m per 2 h; the corresponding values for the maltose solution were 75.5 and 120.2 mg/m per 2 h. In both cases the differences were significant (P< 0.001). Differences between N secretion into glucose and maltose solutions were not significant, either without or with guar gum.

6. Guar gum addition had a greater effect on N secretion in hours 5 and 6 than in hours 1 and 2 of perfusion.

7. It was calculated that guar gum would have increased N secretion by the mucosa of the whole small intestine from approximately 15 to 27 g/d under the conditions of the study, assuming uniform secretion throughout the organ. These results suggest that certain types of dietary fibre may be important determinants of N secretion by the mucosa of the small intestine. They also suggest that changes in N secretion of this magnitude are of importance in N metabolism because the overall rate of protein synthesis in these pigs was probably about 100 g/d (expressed as N), using values from the literature.

1. The aleurone layer, grain coat and embryo which constitute rice bran are rich in vitamins, lipids, protein and lysine compared with the endosperm (milled rice).

2. A method was developed to measure the in vitro protein digestibility of raw and cooked brown rice and their histological components.

3. The protein digestibility of cooked endosperm by the in vitro method agreed with that of other workers using in vivo techniques.

4. The protein digestibility of the aleurone layer and grain coat from raw rice was only 25% but increased to 65% from cooked rice, due to disruption of the cellulosic cell walls at 100°, which was shown by electron microscopy.

5. The decreased protein digestibility due to cooking was not the result of formation of ε-lysyl–γ-glutamyl isopeptide cross-links, but may be due to formation of a cystine-rich core that is resistant to proteases.

6. The protein digestibility of cooked brown rice was approximately the same as that of cooked milled rice, hence it is advantageous for those for whom rice is a staple food to consume brown rather than milled rice.

1. Testosterone (1 mg/kg body-weight per d) given subcutaneously to female rats increased their growth rate and food conversion efficiency but not their food intake compared with that of the placebo-oil controls. A higher dose of testosterone (10 mg/kg body-weight per d) failed to increase the daily weight gain.

2. The increased growth rate of the testosterone-treated rats appeared to occur in the whole body and not specifically in muscle. There were no significant changes in body composition.

3. The fractional synthetic rate of gastrocnemius muscle protein was higher in the hormone-treated rats than in controls. This contrasts with previous results for the anabolic agent trenbolone acetate and reflects differences in the mode of action of these two different steroids, both with androgenic properties.

1. The effects of magnesium Supplementation on Mg absorption proximal and distal to the pylorus in ewes maintained on a grass diet were investigated using a combination of balance, digesta flow and electropotential Measurements.

2. Three mature ewes each received by intrarumenal infusion a supplement of 0, 1, 2 and 3g Mg/d in sequence over four 10-d periods.

3. Net Mg absorption distal to the pylorus took place down its electrochemical gradient, although the quantity absorbed remained small during the control and first infusion periods.

4. The bulk of Mg absorption occurred before the pylorus and, during the control and first infusion periods, took place against its electrochemical gradient. The net Mg absorption proximal to the pylorus rose with declining efficiency as Mg intake was increased. It is suggested that saturation of the absorption process at this site was occurring.

1. Estimates have been made of the irreversible loss of alanine and of glycine in chronically catheterized fetal lambs and in sucking lambs using [U-14C]-labelled radioisotopes. The experiments in the fetal lambs were carried out at least 5 d after implantation of catheters.

2. The mean concentration of glycine in fetal femoral arterial blood between 102 and 129 d conceptual age was 755 μmol/l and this was not significantly different from that in maternal venous blood. The mean concentration of alanine in fetal femoral arterial blood during the same period of gestation was 229μmol/l and this was significantly greater than that in maternal venous blood.

3. Assuming a catenary model, the mean irreversible loss of glycine, determined using the single-injection technique, in three fetal lambs of 107, 111 and 127 d conceptual age was 17 μmol/min per kg, whereas in two fetal lambs aged 106 and 109 d into which the isotope was infused continuously the mean irreversible loss, calculated from the specific activity of glycine 5 h after the start of infusion of the tracer ('pseudo plateau'), was 12 μmol/min per kg. In a sucking lamb, 9 d after birth, the irreversible loss of glycine was 11 μmol/min per kg. The mean irreversible loss of alanine, determined by the single-injection technique assuming a catenary model in five fetuses between 112 and 121 d conceptual age was 14μmol/min per kg, and in two sucking lambs, 9 and 11 d after birth, it was 5.1 μmol/min per kg.

4. When a two-pool model was assumed in which entry of metabolite was not directly into the sampling pool but was by way of the second pool, then the mean irreversible loss of glycine in the three fetuses was 23 μmol/min per kg and of alanine in the five fetuses was 32 μmol/min per kg. Calculations based on the alternative two-pool model did not alter appreciably the rates of irreversible loss of either alanine or glycine in the sucking lambs.

5. From a comparison of the specific activities of the amino acids and of carbon dioxide in blood during the course of the experiments, it was found that in the fetuses 0.96% of the CO2 present in blood was derived from alanine and only 0.12% was derived from glycine. It was calculated that not more than 1.6 μmol lanine/min per kg and 0.29 μmol glycine/min per kg could have been converted to CO2 in the fetal lambs.

6. It is concluded that since glycine in fetal blood originates from fetal tissues and not from direct transfer across the placenta the upper value for the irreversible loss describes metabolism best. In the case of alanine, which is derived from both the maternal circulation and from metabolism in fetal tissues, the true rate of irreversible loss must lie between the values predicted by the two models.

1. Male weanling rats were fed on diets either adequate (55 mg/kg), or severely deficient (0.4 mg/kg) in zinc, either ad lib. or in restricted amounts in four experiments. Measurements were made of growth rates and Zn contents of muscle and several individual tissues.

2. Zn-deficient rats exhibited the expected symptoms of deficiency including growth retardation, cyclic changes in food intake and body-weight.

3. Zn deficiency specifically reduced whole body and muscle growth rates as indicated by the fact that (a) growth rates were lower in ad lib.-fed Zn-deficient rats compared with rats pair-fed on the control diet in two experiments, (b) Zn supplementation increased body-weights of Zn-deficient rats given a restricted amount of diet at a level at which they maintained weight if unsupplemented, (c) Zn supplementation maintained body-weights of Zn-deficient rats fed a restricted amount of diet at a level at which they lost weight if unsupplemented (d) since the ratio, muscle mass:body-weight was lower in the Zn-deficient rats than in the pair-fed control groups, the reduction in muscle mass was greater than the reduction in body-weight.

4. Zn concentrations were maintained in muscle, spleen and thymus, reduced in comparison to some but not all control groups in liver, kidney, testis and intestine, and markedly reduced in plasma and bone. In plasma, Zn concentrations varied inversely with the rate of change of body-weight during the cyclic changes in body-weight.

5. Calculation of the total Zn in the tissues examined showed a marked increase in muscle Zn with a similar loss from bone, indicating that Zn can be redistributed from bone to allow the growth of other tissues.

6. The magnitude of the increase in muscle Zn in the severely Zn-deficient rat, together with the magnitude of the total losses of muscle tissue during the catabolic phases of the cycling, indicate that in the Zn-deficient rat Zn may be highly conserved in catabolic states.

1. In a comparative-slaughter experiment, individually rationed wether lambs initially of 42 kg were given 235, 362 or 456 kJ metabolizable energy (ME)/kg live weight (LW)0.75 per d as sodium hydroxide-treated barley straw with urea (six lambs per treatment), or NaOH-treated barley straw with urea plus 125 g/d white-fish meal to give 307 or 488 kJ ME/kg LW0.75 per d (seven lambs per treatment) for 92 d.

2. All unsupplemented lambs lost both fat and body protein. The changes in fat were – 3.53, – 2.75 and – 1.40 (SE 0.59) kg (initial value 8.6 kg), and the changes in body protein were –0.47, –0.09 and –0.14 (SE 0.13) kg (initial value 4.9 kg) for the three unsupplemented groups respectively. When supplemented with fish meal, fat was again lost as –1.53 and –0.93 (SE 0.55) kg, but wool-free body protein was increased, and gains were 0.48 and 0.89 (SE 0.12) kg for the two supplemented groups respectively. All animals lost wool-free body energy, total changes being –150, – 111, – 59 and –49 and – 16 MJ respectively. When corrected to an equal ME intake the supplemented lambs, when compared with the unsupplemented lambs, gained (instead of losing) body protein (P < 0.001) and lost less fat (P < 0.05). Wool growth did not respond to supplemental protein, but was related to ME intake with an increase of 0.78 g wool fibre for each additional MJ ME.

3. The maintenance requirements of the unsupplemented and supplemented groups respectively were estimated by regression analysis to be 554 and 496 kJ ME/kg LW0.75 per d. The apparent utilization of ME below energy equilibrium (km) was 0.31 (SE 0.08) for the unsupplemented animals, and 0.12 (SE 0.10) for the supplemented animals, well below akm, of 0.70 which current UK standards (Agricultural Research Council, 1980) would predict. Most of these differences could be reconciled if basal metabolism was assumed not to be constant.

4. It is concluded that lambs in negative energy balance can continue lean body growth at the expense of body fat, provided sufficient dietary protein is available. It is also concluded that since the animals at the lowest ME intakes required less ME than predicted by current feeding standards, the effect was that it would have been difficult to distinguish between the apparent utilization of ME for maintenance (km) and for fattening (kf).

1. In search of other provitamins A, the metabolism of cryptoxanthin was studied in several species of freshwater fish, i.e. Chunna gachua, Labeo boga (retinol-rich) and Heteropneustes fossilis (dehydroretinol-rich). The fish were either allowed to starve for 20–25 d to make their intestines free from carotenoids and vitamin A or kept on a vitamin-A-deficient diet for 140–150 d to deplete the initial reserve of vitamin A in the livers.

2. Retinol-rich freshwater fish such as C. gachua and L. boga converted cryptoxanthin into retinol and no 3-dehydroretinol or 3-hydroxyretinol could be isolated from those fish that received cryptoxanthin.

3. 3-Hydroxyretinol and 3-dehydroretinol were isolated from the vitamin-A-deficient H. fossilis, a 3-dehydro-retinol-rich freshwater siluroid, after the administration of cryptoxanthin.

1. The degradation of a swede (Brussica nupus L., cv. Danestone) diet anterior to the terminal ileum was studied in two pigs fitted with T-shaped cannulas 150 mm before the ileo-caecal junction. Digestibility was calculated with reference to chromic oxide and polyethylene glycol.

2. In addition to the total loss of free glucose and fructose, there were substantial modifications to cell-wall material recovered in digesta. These included the apparent loss of 46–50% of uronic acid residues, 72–78% of phenolic material and 10–24% of cellulose initially present in the feed, and a partial solubilization of some hemicellulose components.

3. Since ‘fibre’ recovered at the terminal ileum differed in a number of important respects from ingested fibre, a number of methods for the analysis of dietary fibre were examined to establish (1) the extent to which analysis of feed represented material recovered at the terminal ileum and (2) whether such methods could be applied directly to digesta samples. Results were compared with a complete analysis of water-soluble (620 g/kg dry matter) and water-insoluble (380 g/kg dry matter) fractions of feed.

4. Chemical fractionation techniques gave more reliable quantitative estimates of fibre than in vitro enzymic digestion methods which overestimated fibre. Acid- and neutral-detergent methods both gave too low an estimate of fibre. As none of the methods could allow for the loss of components (particularly pectic polysaccharides) found by sampling at the terminal ileum, none gave an accurate qualitative or quantitative representation of fibre at this point in the gut.

5. It is suggested that, as vegetable fibre recovered at the terminal ileum has already undergone partial hydrolysis, a more dynamic model of dietary fibre, in which the action of gut micro-organisms is considered, may be required to establish possible physiological roles of fibre or fibre components in the digestive tract. Recovery of digesta from sites of interest may be the only way of reliably estimating fibre or specific fibre components at different levels of the gut. This approach to dietary fibre may be impractical when applied directly to humans but the digestive tract of the pig may be a suitable alternative model.

1. In separate experiments the isoleucine and leucine requirements of the kitten were determined on the basis of growth and nitrogen retention. The dietary concentrations of isoleucine tested were (g/kg diet) 1.4, 2.2, 3.0, 3.8, 4.6 and 9.0 with adequate (12.0 g/kg diet) leucine. The levels of leucine tested were (g/kg diet) 5.0, 7.5, 9.0, 10.5, 12.0 and 20.0 in diets containing adequate (9.0 g/kg diet) isoleucine. In both experiments six male and six female kittens received each dietary level of isoleucine or leucine for periods of 10 d in a balanced 6 x 6 Latin-square experimental design.

2. Asymptotic curves were fitted to the response relationships and the minimal dietary requirements for maximal response were estimated from the values at 0.95 of the asymptote. On this basis, the requirements for maximal growth were 6.2 g isoleucine/kg and 7.8 g leucine/kg diet. The requirements for maximal N retention were higher; 8.4 g isoleucine and 10.6 g leucine/kg diet. The isoleucine requirements suggested by this method are probably overestimations and might be slightly above 4.6 g/kg diet.

3. Plasma isoleucine and leucine concentrations were not useful in estimating the requirements. Plasma leucine increased rectilinearly with increasing dietary leucine while the response of plasma isoleucine to increasing dietary isoleucine was non-rectilinear. Neither response relationship exhibited a breakpoint at the level of requirement. Below the suggested minimal requirement for leucine there were significant increases in the concentrations of isoleucine and valine in the plasma. Dietary isoleucine below the level of requirement had no effect on plasma valine and leucine. Dietary leucine had no effect on the plasma concentrations of methionine, phenylalanine and threonine, suggesting that the effect of decreasing dietary leucine on plasma isoleucine and valine is a result of decreased oxidation rather than decreased protein anabolism.

4. In a separate experiment six kittens, presented a diet containing 2.2 g isoleucine/kg, developed crusty exudates around their eyes within 27 d and six kittens, presented diets containing 3.8 g isoleucine/kg, showed this clinical sign but with less severity within 47 d. Cultures of conjunctival swabs taken from the most severely affected kittens showed the presence of staphylococcal species, suggesting that in isoleucine-deficient kittens there was impaired resistance to these dermal microbes.

1. Lambs were given a diet of oaten chaff-sucrose-fishmeal(48:48:4, w/w) and either 60 (diet A) or 120 (diet B) g urea/kg sucrose in the diet. All animals were defaunated and half were refaunated. Each group of lambs (faunated and defaunated) was then divided into two groups and given diet A or diet B. Feed intake, wool growth and live-weight change were monitored over a 182 d period.

2. The level of urea supplementation had no effect on wool growth or live-weight gain.

3. Defaunated lambs gained live weight at a higher rate (9%, P < 0.06) and grew 37% more wool (P < 0.01) than the lambs with large populations of protozoa in their rumens.

1. Four experiments were carried out to identify and quantify the limiting amino acids (AA) in rumen microbial protein (RMP).

2. A method was developed which involved first, an assessment of the efficiency of utilization of absorbed AA-nitrogen (U) of RMP, defined as the retention of AA-N from RMP absorbed from the small intestine, and second, addition of a mixture of AA similar to the absorbed AA profile in a quantity defined by the U of RMP and equal to (1 – U)/U. Third, it involved removal of each AA in turn and measurement of the resultant N retention. Using this approach it was possible to calculate both the order and extent of AA limitations in RMP.

3. Apart from methionine which was found to be the most limiting AA, only lysine, arginine and histidine reduced N retention when omitted, and accordingly only these AA were limiting in RMP.

4. The method is discussed in detail and the amount of supplementary AA required to utilize RMP fully is calculated.

1. A mathematical model is described, which simulates the metabolism of absorbed nutrients (amino acids, acetic acid, butyric acid, glucose, lipid and propionic acid) in growing sheep.

2. The basic assumption of the model is that each nutrient is partitioned between synthetic, oxidative or intermediate reactions with rates of reaction which are described using enzyme kinetics. These rates depend on the relationship between maximum reaction rates, constants of affinity and inhibition and the concentrations of metabolites as determined by the model.

3. Synthetic reactions calculate fat and protein deposition while intermediate reactions involve the production of ATP and NADPH. There is a total of twelve state variables and the model, programmed in CSMP and ACSL, is solved by integration of twelve differential equations.

4. The model calculates the efficiency of utilization of metabolizable energy for different nutrient inputs and the results may be interpreted in terns of fluxes through the metabolite pools. Simulations using inputs representing forage- and concentrate-based diets indicated decreased efficiency for the forage at high levels of intake and possible reasons for this were further studied in simulations where the inputs of protein and glucose were varied.