1. The vitamin A content of human liver tissue was determined in 363 autopsy samples. The sample comprised a total of 181 subjects dying after accidents and 182 dying from coronary heart disease among Singapore ethnic groups of both sexes.

2. The medium vitamin A reserve was 146 mg/kg in accident victims and 141 mg/kg in those who had died of coronary heart disease. Of all the samples 16% contained less than 40 mg/kg, 45% had 100–300 mg/kg, while 9% contained more than 500 mg/kg liver.

3. Among the accident victims, Indians had the lowest median liver vitamin A reserve (118 mg/kg) compared with that in other ethnic groups (137 mg/kg in Chinese, 191 mg/kg in Malays, 155 mg/kg in Caucasians).

4. The ethnic distribution of vitamin A reserve in coronary deaths was similar to that in accident victims.

5. There was no significant difference between the sexes in hepatic vitamin A reserve.

6. The distribution of vitamin A reserve in all the groups was skewed to the right.

1. The amounts of magnesium, copper, zinc, phosphorus, manganese, potassium, vitamin B6, vitamin B12, folate, pantothenic acid, biotin, vitamin E and dietary fibre in the British household diet were calculated by applying appropriate values from recent analytical studies to the amounts of foods recorded in the National Food Survey during 1986.

2. National average intakes were (mg/person per d): Mg 247, Cu 1.25, Zn 9.0, P 1249, Mn 3.43, K 2694, vitamin B6 1.73, vitamin B12 6.33μg, folate 230μg, pantothenic acid 6.07, biotin 35μg, vitamin E 8.4. Regional and income-group differences were estimated, and found to be small. Additional contributions from alcoholic drinks and confectionery were also determined.

3. Dietary fibre was estimated both as unavailable carbohydrate and as non-starch polysaccharide. The national average intakes were 21.8 and 12.9 g/d respectively.

4. Intakes were compared with Canadian (Department of National Health and Welfare, 1983) and American (National Research Council, 1980) recommended dietary allowances (RDAs). With the exception of biotin, the Canadian RDAs were met by the household diet but the much higher American RDAs were only met for vitamin B12 and pantothenic acid.

1. Changes in basal metabolic rates (BMR), following alterations in the preceding day's dietary protein (8.6, 11.5 and 14.0% of energy) were studied in eight, young, healthy adults over 4d.

2. Results showed a significant training effect, with BMR values 4.8 % lower on day 4 of the study period. Analysis of the results by ANOVA revealed a significant interaction between subjects and diets (P<0.005), a significant difference between subjects but no differences in BMR due to the protein content of the diets.

3. Mean coefficient of variation (CV) for intra- and inter-individual differences in BMR from day-to-day was of the order of 4 and 9% respectively.

4. Changes in protein content of the preceding day's diet do not influence variations in BMR which appear to be random in nature with a true CV of 3.8%.

1. The energy balance and activity allocation of eight male and eight female Indian farmers were meaured for 4 d during 10 months in both the dry and wet seasons of 1983.

2. All food prepared and eaten was weighed and nutrient values were calculated from food composition tables.

3. Average energy costs per unit mass for fifteen tasks were estimated from data obtained using a Kofranyi-Michaelis respirometer. Each subject was observed from 05.00 to 20.00 hours and activities were recorded for each minute. The remaining activity was determined by recall.

4. Activity allocation was categorized qualitatively into time spent on economically productive work, free time and body maintenance.

5. The mean weight for male subjects was 48.2 kg; the average female weight was only 36.9 kg. The mean height for male and female subjects was 1.61 m and 1.49 m respectively.6. For male subjects, the daily mean energy intake of 9.81 MJ (2350 kcal) was close to the calculated energy output of 9.54 MJ (2285 kcal).

7. The women's calculated daily expenditure of 8.22 MJ (1968 kcal) was slightly higher than their mean energy intake of 7.73 MJ (1852 kcal).

8. Although intake and output varied in relation to sex, weight and wealth the mean intake per kg body mass was equal for both males and females at 210 kJ (50 kcal) per kg. This is close to the minimum requirement for active Third World farmers.

9. The women spent significantly more time on economically productive work activities than the men (11.1 v. 8.1 h/d). Although female energy intake was 27 % less than males, their productive work time was 27% higher.

1. Possible links between metabolism and satiation were investigated using volunteer subjects given test meals based on milk solids. Satisfaction was rated by the subjects on a six-point scale and the course of metabolism was followed by measurement of the respiratory quotient (RQ).

2. The time-course of satiation was the same for a high-carbohydrate, a high-fat and a high-protein meal, in spite of the very different time-course of metabolism. The degree of satiation was reduced by added sodium chloride, without affecting the RQ rise. On the other hand, calcium chloride produced a suppression of the RQ rise without altering the satiation.

3. It is proposed that the results indicate that the primary receptors responsible for post-prandial satiation lie within the gut wall and that there is probably a number of receptor types. Likely candidates for these receptors are the gut hormone-secreting cells.

4. Although very-low-protein meals produce less satiation than meals containing 220 g protein/kg dry weight, there is no additional satiation obtained by increasing the protein level further. This is not inconsistent with the possibility of a protein hunger separate from an energy hunger.

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. 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. 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. 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. 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.

1. Protein synthesis was estimated in vivo in breast (superficial pectoral) and tibia (gastrocnemius) muscles, liver, kidney, pancreas, crop, duodenum, jejunum and ileum, using L-[U-14C]lysine injection. The effect on incorporation of [14C]lysine 1 and 2 h after injection was examined in five chickens adapted or not adapted to intermittent feeding.

2. Incorporation of [14C]lysine into tissue decreased in magnitude in the following descending order: pancreas > jejunum, duodenum > ileum, crop, liver > kidney > tibia, breast muscle and blood plasma.

3. The incorporation of [14C]lysine into muscle protein was higher in chicks after 24 h of refeeding than after 24 h of food deprivation. These differences were higher in adapted than in non-adapted birds. On days of refeeding the rate of incorporation exceeded that found in chickens fed ad lib.

4. Bound 14C from lysine in the intestinal segments was less than in control birds after food deprivation and greater after refeeding in non-adapted chicks only.

5. A negative relation was observed between bound and free 14C in muscles and in other tissues.

6. Short- and long-term adaptations to feeding regimens are discussed.

1. Results of 138 nitrogen balance studies from experiments with forty male Limousin and nineteen male Ile de France preruminant lambs were used to estimate total N requirements and to assess the effects of dietary tricaproin inclusion, protein concentration, lysine and methionine supplementation and the age of lambs on protein retention. In addition, energy balances were obtained in twenty-four of the Limousin lambs from birth up to 3 weeks of age by means of a slaughter technique.

2. For milk substitute unsupplemented with amino acids, tricaproin inclusion increased N balance slightly (P < 0.001) when a medium-protein concentration (260 g/kg dry matter (DM)) was used, in 2-week-old lambs (+4.3%) and in 5-week-old Limousin lambs (+5.3%), or very markedly when a high-protein concentration (320 g/kg DM) was used, in 2-week-old lambs (+14.5%) and in 5-week-old lambs (+18.6%). Protein requirements decreased from 300 g/kg DM in 3-week-old lambs to 270 g/kg DM in 5-week-old lambs for the control milk containing tallow-coconut oil mixture (0.67:0.33 by wt) and was increased above 300 g/kg DM at all ages in the case of experimental milk containing tallow-coconut oil-tricaproin mixture (0.33:0.33:0.33, by wt).

3. For milk containing either a medium- or a high-protein concentration and supplemented with lysine and methionine, inclusion of tricaproin increased N balance (P < 0.01) to a similar extent (+8.5 up to +14.3 %) in 1 to 2- and 3-week-old Limousin lambs. An increase in N concentration in the milk had no effect in 1 - and 2-week-old lambs, but led to a decreased N balance in 3-week-old lambs. Protein requirements decreased from 310 g/kg DM in 1-week-old lambs to 190 g/kg DM in 3-week-old lambs for the milk containing tallow-coconut oil or from 300 g/kg DM in 2-week-old lambs to 210 g/kg DM in 3-week-old lambs for the milk containing tallow-coconut oil-tricaproin.

4. For the Ile de France lambs given milk supplemented with lysine and methionine, tricaproin inclusion did not alter N balance. Protein requirements decreased from 370 g/kg DM in 2-week-old lambs to 270 g/kg DM in 4-week-old lambs for milk containing both kinds of fat mixtures.

5. Between birth and 3 weeks of age, efficiency of metabolizable energy (ME) utilization in the Limousin lambs was not dependent on the nature of the milk fat or the protein concentration of the diet (ME efficiency for tissue deposition varying from 0.672 to 0.698) whilst ME efficiency for protein deposition was 0.52 and ME efficiency for lipid deposition was close to 1; daily maintenance expenditure was 553 kJ/kg body-weight0.75

1. Blood from chronic indwelling catheters in the caudal aorta and anterior mesenteric, gastrosplenic and hepatic portal veins was used to measure blood flow and net flux of oxygen, glucose and nitrogenous compounds across hepatic portal-drained viscera (PDV), post-stomach (anterior mesenteric-drained viscera (MDV)) and stomach tissues of two beef steers (390 kg mean live weight).

2. Steers were fed in sequence on (1) chopped lucerne (Medicago sativa) hay (twelve meals/d), (2) chopped lucerne hay (two meals/d) and (3) a pelleted concentrate diet containing 780 g ground maize/kg (two meals/d). The lucerne hay and concentrate contained 26.5 and 16.8 g nitrogen/kg respectively.

3. Five measurements of net flux (blood flow multiplied by venous-arterial concentration differences (VA)) were obtained hourly on 2 d for each dietary regimen, beginning 0.5 h before feeding at 08.00 hours. Blood flow was measured by downstream dilution of p-aminohippurate (PAH).

4. Blood flow across MDV averaged 42% of PDV blood flow (665 litres/h).

5. Net use of O2 across MDV accounted for 51 % of net PDV use of O2 (920 mmol/h). This disproportionate use of O2 in relation to blood flow was due to greater VA for O2 across MDV than across stomach tissues. Dietary regimen had no effect on the proportions of PDV blood flow and net O2 consumption attributable to MDV or stomach tissues.

6. When lucerne was given, net glucose use across MDV represented 69% of PDV use (35 mmol/h). When concentrate was given, MDV glucose use switched to net absorption (29 mmol/h), reducing net PDV glucose use to I mmol/h.

7. When concentrate was given, net MDV absorption of α-amino-N (AAN) increased from 98 to 190 mmol/h, yet net PDV absorption (101 mmol/h) was not affected. Net stomach AAN flux increased from -7 to -69 mmol/h when concentrate was given, negating the increase in net MDV absorption.

8. Net absorption of ammonia-N across MDV represented 28 and 52% of net PDV absorption when lucerne and concentrate were given respectively. Net NH3-N absorption across PDV was lower when lucerne was given than when concentrate was given (295 v. 154 mmol/h), reflecting lower dietary N intake (153 v. 83 g/d). Net MDV absorption of NH3-N was not affected by diet. Net removal of blood urea-N (BUN) across PDV (101 mmol/h) was not affected by diet. Across MDV, BUN removal was lower when concentrate was given than when lucerne was given (32 v. 77 mmol/h). In beef steers, MDV tissues account for substantial portions of net flux of non-protein-N across PDV and are responsible for essentially all PDV absorption of AAN.

1. Net flux of volatile fatty acids (VFA), D-β-hyroxybutyrate (BOHB) and L-lactate across post-stomach (anterior mesenteric-drained viscera (MDV)), stomach and total hepatic portal-drained viscera (PDV) tissues was measured in two beef steers (mean live weight 390 kg).

2. Net flux was measured while steers were fed, in sequence, on (1) chopped lucerne (Medicato sativa) (twelve meals/d), (2) chopped lucerne (two meals/d) and (3) a pelleted concentrate diet containing 780 g ground maize/ kg (two meals/d).

3. Five hourly net flux measurements were obtained on 2 d for each dietary regimen, beginning 0.5 h before a meal delivered at 08.00 hours. Net flux was calculated as venous-arterial concentration differences (VA) multiplied by blood flow (measured by downstream dilution of p-aminohippurate (PAH)).

4. Stomach tissues accounted for 85 to over 100% of net VFA and BOHB appearance across PDV. Net appearance across stomach tissues represented 74% of net PDV L-lactate appearance.

5. When lucerne was given, there was net utilization of arterial acetate and BOHB across MDV. This MDV utilization may reflect acetate and BOHB use as an energy source or their incorporation into mesenteric fat.

6. When concentrate was given, more n-butyrate and n-valerate and less L-lactate appeared across PDV and less 3-methylbutyrate appeared across stomach tissues than when lucerne was given. Postprandial increases in VFA, BOHB and L-lactate net flux across PDV followed meal-feeding of lucerne.

7. On a net basis, the relative contribution of MDV tissues to total PDV net appearance of VFA and BOHB was small (< 15%) in these steers.

1. Lean (Fa/–) and obese (fa/fa) Zucker rats were adrenalectomized or sham-operated at 18 d of age (3 d before weaning). After weaning the rats were fed ad lib. on semi-synthetic diets containing either a low (8 g/kg) or a high (178 g/kg) proportion of fat. Other groups of sham-operated rats were given the same amount eaten by adrenalectomized animals (restricted intake). Rats were killed at 40 d of age.

2. Adrenalectomy reduced the body lipid content of lean and obese rats compared with intact animals fed ad lib. or given a restricted intake. Adrenalectomized obese rats contained more body lipid than intact or adrenalectomized lean rats.

3. Sham-operated obese rats given a restricted intake had less body protein than similarly treated lean animals and this phenotypic difference was abolished by adrenalectomy.

4. There were no effects of diet on growth or body composition of intact or adrenalectomized rats.

5. It is concluded that preweaning adrenalectomy prevented development of the obese phenotype when rats were fed on either diet. Comparison of these results with a previous study, in which adrenalectomized Zucker rats were fed on a stock diet (Fletcher, 1986b), showed, however, that feeding either of the semi-synthetic diets caused greater deposition of body lipid in obese rats.

1. The basic assumptions involved in one- and two-compartment models with age-independent distributed residence times (exponential, G1) for describing digesta flow are reviewed as the bases for describing families of one- and two-compartment models which assume age-dependent distributions (Gn) of residence times.

2. The two-compartment, age-independent model with exponentially distributed residence times (GIGI) yielded estimates of essentially equal rate parameters when fitted to faecal values for all four cows receiving a diet of 500 g coarsely chopped, sodium hydroxide-treated straw /kg and one of four cows receiving the same diet but with ground and pelleted straw. The incorporation of progressively higher orders of age dependency (G2-G6, Gn) into the faster turnover compartment of two-compartment models (GnG1) resulted in a resolution of equal rate parameters estimated by the G1G1 model and a reduction in standard errors for the rate and the initial concentration parameters.

3. The occurrence of equal rate parameters in two-compartment models indicated an age-dependent process; a process which could equally well be described by a one-compartment, age-dependent compartment having an order of age dependency equal to the sum of these orders in the two-compartment model with equal rate parameters.

4. The age-independent models overestimated time of first appearance in the faeces of a meal's particles. The association of age dependency with the faster turnover compartment resulted in earlier estimates for first appearance of the marked particles; estimates which were more consistent with observed first appearance.

5. The faecal excretion pattern from cows fed on the ground and pelleted straw diet exhibited an age-independent distribution of longer residence times which dominated approximately 80% of the later residence times. Age-dependent, one-compartment models gave a poor fit to such data from these cows fed on ground and pelleted straw. In contrast, age-dependent, one-compartment models provided an excellent fit to data from cows fed on chopped straw; data which indicated that age-independent distributions of residence times were much delayed in appearing or were totally absent.

6. The mean residence time for the slower turnover, age-independent compartment estimated from faecal excretional of stained particles from either diet was similar to that estimated from duodenal concentrations of the stained particles. This suggests that the slower turnover model compartment was confined to preduodenal sites.

7. The mean residence time for the faster turnover, age-dependent compartment estimated from duodenal data was 58–62 % that estimated from faecal data and suggests that the site of this model compartment was both pre- and post-duodenal.

8. It is emphasized that the slow and imperfect mixing of particulate matter that occurs in reticulo-rumen digesta is inconsistent with the assumptions of instantaneous and homogeneous mixing made by models having age-independent distributions of residence times. The use of age-dependent distributed residence times can accommodate such imperfect mixing and is consistent with the existence of age-discriminating processes involved in particle flow from the reticulo-rumen. Age dependency also offers improved precision in estimating parameters of digesta flow via processes having inherent uncertainty in their mixing and age-discriminating mechanisms.