1. Serum and intracellular distribution of retinol was determined in equines maintained on four levels of vitamin A intake.

2. The form of retinol transported in serum was determined by gel filtration and chromatography to be a complex of retinol bound to a protein of molecular weight (MW) of approximately 20000, which was in turn complexed probably with prealbumin to yield a complex with a MW of 75000 to 80000.

3. Increasing dietary vitamin A levels enhanced the concentration of lipoprotein-bound retinyl esters in the plasma.

4. Vitamin A in the liver cytosol was found predominantly as retinyl esters in a lipid–protein aggregate of MW approximately 2 × 106 and hydrated density of 1·063–1·111. In the kidney and adrenal gland, two Iipid–protein entitites were found with MW of approximately 1·8 × 106 and 1·7 × 105 respectively. These fractions contained approximately 40 and 20% lipid respectively and had densities of 1·063–1·111 and approximately 1·21.

5. All lipid–protein aggregates were associated with retinyl palmitate hydrolase activity and guanidine treatment released a 15000 MW material, presumably intracellular retinol-binding protein.

6. Increasing dietary vitamin A enhanced the proportion of retinol in the 1·7 × 105 fraction.

7. Findings in equine plasma and liver resemble previous observations in other species. The characterization of two new lipid–protein aggregates in equine kidney and adrenal glands, which have hydrolase activity, may be important in intracellular retinol transport and metabolism, especially in animals subjected to high intakes of vitamin A.

1. Four pairs of Scottish Blackface ewes were given a basal diet of hay, providing 8 mg zinc/d, and one of four levels of supplementary Zn (0, 75, 150 or 225 mg/d) continuously by intraruminal infusion.

2. 65Zn (59 μCi) was given intravenously after stabilization for 14 d and the changes in specific radioactivity (SR) of plasma and faeces were monitored for a further 10 and 13 d respectiveiy. The faecal endogenous losses and absorption of Zn were estimated, using the principle of isotope dilution, by two methods using the whole or latter parts of SR: time curves.

3. Faecal endogenous losses were estimated by the part area method to be 4·9, 6·4, 5·1 and 6·3 ± 0·35 mg/d at 0, 75, 150 and 225 mg supplemental Zn/d i.e. largely unaffected by Zn intake and averaging 0·11 mg/kg live weight (LW). The whole area method gave similar results.

4. Urinary excretion was negligible (probably < 0·2 mg/d) for all sheep.

5. The amount of Zn absorbed was assumed to equal the irreversible loss of Zn under steady-state conditions and found to remain constant at 7·6±0·39 and 10·3±0·6 mg/d when calculated by ‘whole’ and ‘part area’ methods. Zn retention did not increase with Zn intake and homoeostasis was achieved primarily by control of Zn absorption which fell from 0·75 to 0·03 or from 0·96 to 0·05 of intake, depending on method of calculation, as intakes increased.

1. Patients with cataract were classified into undernourished (twenty-eight subjects) and well-nourished (twenty-seven subjects) groups based on the anthropomtric index, weight (kg)/height (m)2. Those with a value for the index of less than 18 were considered as undernourished.

2. Lenses were classified into four groups on the basis of nuclear colour as proposed by Pirie (1968). Lenses of pale uniform colour or yellow colour were included in group 1, those with brownish-yellow nucleus in group 2, those with a yellowish-brown nucleus in group 3 and those with brown nucleus in group 4.

3. Irrespective of group, the wet weight, dry weight, percentage moisture and total protein content of cataractous lenses from undernourished patients were similar, as were the corresponding values for well-nourished patients. On the other hand, the percentage of soluble proteins in lenses tended to decrease with deepening of nuclear colour in both groups of patients. Further, soluble protein concentrations in lenses from undernourished patients were significantly lower as compared to those from well-nourished patients.

4. The results suggest that nutritional factors could influence the composition of cataractous lenses.

1. Raw soya-bean meal (RS) was fractionated into soya-bean lyophilized extract (SLE), soya-bean lyophilized residue (SLR), acid-precipitated proteins (APP) and whey proteins.

2. Trypsin (EC 3.4.21.4) and chymotrypsin (EC 3.4.21.1) inhibitors (TI) were soluble at pH 8 and remained soluble after the extract was acidified to pH 4·4. Except for whey, heating abolished, almost totally, their inhibiting activity.

3. Feeding SLE diet (high TI content) and APP diet (low TI content) resulted in growth depression below the RS level. Feeding the SLR diet resulted in an optimal growth. Feeding diets containing heated fractions improved the growth rate though not to the level observed with heated RS (HS) diet.

4. RS, SLE, APP and whey diets produced similar pancreatic enlargement which could be totally (RS, whey) or partially (SLE, APP) abolished by heating.

5. Feeding the RS diet reduced pancreatic amylase content. The factor responsible for this effect cofractionated with SLE and whey proteins.

6. Two groups of factors in the various diets were probably responsible for the elevation in pancreatic proteases. The first group were the heat-labile factors present in RS, SLE and whey whereas the second group resisted the heat treatment and were found in APP and SLR.

7. The results suggest that for optimal growth rate of rats, heat treatment should be given to the unfractionated soya-bean proteins rather than to the isolated fractions. The results further indicated that TI are not the only factors that can lead to pancreatic enlargement and changes in pancreatic enzymes composition.

1. Two sows were housed in farrowing crates with slotted floors and fed daily with approximately 200 μCi 198Au from 3 d before farrowing until their piglets were 21 d old.

2. The sows' faeces became radioactive but their milk remained free of radioactivity. The piglets' mean (±SE) whole-body radioactivity was equivalent to 8·5 ± 0·9 g (range 3·8–15·5 g) of faeces. This is probably a measure of their daily intake of faeces.

3. The possibility of using this natural coprophagia to prevent piglet anaemia has been demonstrated on two commercial piggeries by feeding the sows a diet containing 2000 mg Fe/kg.

1. Fermentation and absorption of constituents of digesta in segments of the large intestine of sheep given different diets were studied by analysis of gut contents obtained at slaughter after a period during which the sheep had been administered a non-absorbable gut marker.

2. In sheep given chopped, dried lucerne (Medicago sativa) there was net absorption of water throughout the large intestine with concomitant increases in the proportion of dry matter (DM) And organic matter (OM). There was net disappearance of 62 g OM, 1·66 g non-urea non-ammonia-nitrogen (NU–NAN) and 0·6 g(urea + NH3)-N in the caecum and proximal colon. There was no significant change in OM and NU–NAN flow through the remainder of the large intestine but there was a net disappearance of 0·3 g NH3–N. There was also net appearance of volatile fatty acids (VFA) in the caecum, most of which was apparently absorbed before the rectum.

3. Metabolism in the caecum was also studied in sheep grazing fresh pasture or consuming one of three sugar cane-bagasse-based diets, or barley pellets. In the lucerne- and pasture-fed sheep there was a net disappearance of approximately 0·5 g NH3-N/d from the caecum, while in sheep fed on bagasse plus urea, 1·4 g NH3-N/d was apparently absorbed from this region. The addition of fish meal to this latter diet resulted in apparent disappearance of 5·3 g NH3-N/d from the caecum and proximal colon.

4. There was apparent loss of NU–NAN from the caecum of sheep on all diets except the barley diet. With the latter diet there was a net gain of 1 g NU–NAN/d which was associated with relatively high VFA concentration and production; taken together these results indicate that microbial fermentation in the caecum was more extensive in the sheep fed on the barley diet than in those fed on the other diets.

5. The proportions of individual VFA in digesta from the rumen and caecum of lucerne-fed and pasture-fed sheep and in digesta from the caecum of sheep given the bagasse-based or barley diets are also reported and discussed.

6. In general the results indicate that the caecum and to a lesser extent the proximal colon were the major regions of fermentation and absorption of the components of the digesta in the large intestine.

1. Plasma total cholesterol, high-density-lipoprotein (HDL)-cholesterol total protein, albumin and globulin levels were estimated in blood samples from thirty children with kwashiorkor, thirty-five with marasmus, twenty-eight with marasmic-kwashiorkor and twenty-seven control children.

2. HDL-cholesterol was estimated after the very-low-density and low-density lipoproteins were precipitated from the plasma with heparin and manganese chloride.

3. The distribution of HDL-cholesterol in the control and in the children with PEM was skewed and the range of values was wide. The values were independent of age and sex.

4. After logarithmic transformation of the HDL-cholesterol and HDL-cholesterol: total cholesterol values, the geometric mean values for the three groups of children with PEM were significantly decreased when compared with values for the control children.

5. The decrease in the mean HDL-cholesterol value for the children with kwashiorkor was more than for children with marasmus and marasmic-kwashiorkor.

1. Pancreatic growth was measured in rats by changes in pancreatic weight, nucleic acid content and protein content after feeding diets of heated soya-bean flour (HSF), raw soya-bean flour (RSF), 200 g raw soya-bean flour+800 g heated soya-bean flour/kg (80 HSF) and 400 g raw soya-bean flour+600 g heated soya-bean flour/kg (60 HSF) for periodsup to 36 weeks. Control rats of comparable age to soya-bean flour-fed rats were continuedon rat cubes during the 36-week study.

2. Cube-fed rats remained significantly heavier than rats fed on soya-bean flour diets. Analysis of variance showed rats fed on HSF were significantly heavier than RSF-fed rats and rats fed on 80 HSF significantly heavier than those fed on 60 RSF.

3. Pancreatic indices in HSF-fed rats were similar to comparable control rats.

4. Hypertrophy was found in rats fed on the RSF-containing diets with the extent of enlargement corresponding to the RSF content. Hyperplasia was also found in rats fed on RSFand 60 HSF.

5. The greatest pancreatic growth was seen in RSF-fed rats with all the indices peaking at 8 weeks followed by a decline and then a rise again at 36 weeks.

6. The fall in pancreatic indices in rats fed on RSF for 12 and 24 weeks is most likely an effect of general malnutrition due to the multiple deficiences in amino acids which occur in animals fed on RSF. The rise at 36 weeks may reflect increased body growth or the beginning of adenornatous changes.

1. Experiments were undertaken to examine the errors associated with the use of indigestible markers, the 51Cr-labelled complex of chromium ethylenediaminetetra-acetic acid (51Cr-EDTA) and 103Ru-labelled tris-(1,10-phenanthroline)-ruthenium(II) chloride (103Ru-P), to measure liquid- and solid-phase digesta kinetics in the caecum and proximal colon of sheep.

2. First-order kinetics of markers were observed following either single injection or termination of continuous infusion. There were no differences between the half-times (T½) of marker in the caecum plus proximal colon whether calculated from marker concentration in caecal digesta or in faeces. There were also no differences in the T½ values calculated for the liquid- and solid-phase markers. When pool sizes calculated from the marker kinetics were compared with the volume of digesta present in the caecum and proximal colon at slaughter, it appeared that the 51Cr-EDTA and 103Ru-P caecal pools described the digesta contained in the entire caecum and proximal colon.

3. The flow-rates of dry matter (DM) through the caecum of sheep given 694 g lucerne (Medicago sativa) DM/d were similar whether estimated from total collection of faeces, by single injection of marker, or by the ratio, marker concentration: DM in either caecal digesta or faeces during continuous infusion of marker into either the rumen or the caecum.

4. In sheep given 553 g brome grass (Bromus inermus) DM/d the coefficient of variation of estimates of the plateau of 51Cr-EDTA marker during continuous infusion into the caecum was greater when 130 ml infusate/d were administered than with 1000 ml/d.

5. In the sheep given brome grass the lines of best fit of decline in In 51Cr-EDTA marker concentration v. time following termination of the continuous infusions described previously and following single injection of marker in 20 or 2 ml into the caecum were examined. The variation was least when 1000 ml infusate/d had been administered and was unacceptably large following a single injection of 2 ml.

6. These experiments showed that tracer techniques could provide unbiased estimates of trace kinetics in the caecum and proximal colon.

1. The content of total pantothenic acid (PaA) in two foodstuffs of microbial origin was measured by standard microbiological and chick biological assays.

2. Substantially and consistently higher values were found by the chick assay than by the microbiological determination, indicating that PaA-containing compounds were present that were not utilized by the test micro-organisms but were available for chicks. Attempts to identify these compounds did not explain the source of excess PaA activity for the chick.

3. It is suggested that forms of PaA that are undetected by standard methods of microbiological assay differ from one food to another and require different treatments to make the vitamin available to the assay organism.

1. Although disrupted parturition and high foetal losses have previously been reported in pregnant rats maintained on zinc-deficient diets this is the first report to differentiate between the effects of reduced Zn intake and the effects of reduced food intake on theoutcome of pregnancy in the rat.

2. Rats maintained on a 0·5 mg Zn/kg diet for the last 7 d of gestation or on a 5 mg Zn/kg diet throughout gestation did not consume significantly less food than rats given 10 or 20 mg Zn/kg diets except during the last 2 d of gestation. Pair-feeding of Zn-adequate rats (20 mg/kg) to those given low-Zn diets for the last 2 d of gestation did not affect the outcome of pregnancy in these rats.

3. In the rats maintained throughout gestation on 5 mg Zn/kg or on 0·5 mg Zn/kg in the last 7 d of gestation, parturition onset and duration were not significantly altered. Foetal rvival was very significantly reduced but only from day 22 onwards; before the onset of parturition, foetal survival was not significantly affected by Zn deficiency during gestation.

4. Subcutaneous injection of evening primrose (Oenothera biennis) oil into rats throughout gestation enhanced foetal and neonatal survival in rats given 5 mg Zn/kg but reduced foetal survival in rats given 0·5 mg Zn/kg in the last 7 d of gestation.

5. The results suggest three points: (1) subtotal Zn deficiency during gestation in the rat jeopardises foetal survival at parturition without affecting the onset or duration of parturition, (2) foetal death in rats maintained on Zn-deficient diets occurs only in relation to parturition itself, (3) provided that Zn intake near term is at least 5 mg/kg, supplemental essential fatty acids (evening primrose oil) will reduce foetal mortality during parturition and in the neonatal period.

1. Rats were given a purified folate-deficient diet containing 5 g succinylsulphathiazole/kg for 4–5 months in two experiments. Control rats were supplemented with folic acid in the drinking-water.

2. Weight gain was much below normal in the folate-deprived rats after the first month. Very low folate levels were recorded in blood, liver and peripheral nerve (12–33% of control). In Ihe central nervous system, including the cerebrospinal fluid, the folate depletion was less conspicuous (50–80% of control). Only marginal signs of anaemia were found and no signs of neurological dysfunction were detected, using nerve conduction velocity measurement and co-ordination tests.

3. Light and electron microscopy of the folate deficient liver revealed fatty infiltration, and enlargement of liver parenchymal cells, nuclei and nucleoli. There was often a considerable amount of bile ductular cells in the lobuli but no cirrhosis. The morphological changes resembled those observed in choline deficiency.

4. Phospholipid N-methylation in liver was depressed in folate deficiency. This was probably due to a decreased availability of S-adenosylmethionine caused by the low concentrations of methylated folate in liver. Intraperitoneal administration of methionine did not normalize phospholipid methylation.

5. In folate deficiency the proportion of ethanolamine phosphoglyceride in liver was increased at the expense of choline phosphoglyceride, which is consistent with a decreased phospholipid methylation. Also an increase in liver triacylglycerol was noted, in accordance with the morphological observations. Brain lipid composition was unchanged.

6. After the injection of labelled ethanolamine, isotope accumulated in liver phosphoethanolamine in folate deficiency, probably due to an impairment of the CTP: ethanolaminephosphate cytidylyltransferase(EC 2.7.7.14) reaction. The mechanism of this impairment is discussed.

7. Although the low concentrations of folate was the main nutritional change in the deprived animals, changes with respect to vitamin B12 and maybe also choline cannot be excluded. We conclude that some of the changes in folate deficiency, i.e. fatty liver and decreased biosynthesis of liver phospholipids may be due to a precipitated deficiency of lipotropic agents, whereas other differences may be specific for deficiency of folate per se, such as changes in liver phospholipid fatty acids and some of the morphological aberrations.

1. An immunochemical test for predicting the suitability of different soya-bean products for feeding to preruminant calves was studied. Calves fitted with abomasal and re-entrant ileal cannulas, were first given a series of feeds containing heated soya-bean flour and two with casein as the protein source, and then given further test feeds in which different experimental soya-bean products, prepared under conditions which might be used commercially, provided the nitrogren source. These products (Q, R, S and T) were prepared respectively by extracting fat-free soya-bean flour with aqueous ethanol at 960, 650, 650 and 550 ml/l and at 60, 60, 78 and 78° and then treating the residue with steam for 30 min.

2. After infusion of a test feed into the abmasum measurements were made of transit time through the small intestine, flow-rate of ileal digesta, recovery of polyethylene glycol (a water-soluble marker added to the feed) and net N absorption up to the distal ileum. Glycinin and β-conglycinin, antigenic constituents of soya-bean protein, were determined in saline (9 g sodium chloride/l) extracts of soya-bean products by haemagglutination inhibition assay.

3. After calves had been given a series of four feeds containing heated soya-bean flour, they showed hypersensitivity to the flour by developing disturbances in digesta movement and N uptake. When experiments were made to compare the effects of giving feeds based on casein with those containing products R, S and T it was shown that some differences in transit times and flow-rates of digesta through, and N absorption from, the small intestine occurred. Disturbances were, however, much less than those observed with product Q feeds.

4. Haemaggultination inhibition assay of products Q, R, S and T gave titres (log2 reciprocal of highest dilution of saline extract inhibiting agglutination) of 12, 5, 3 and 2 for glycinin and 13, 3, 3 and 2 for β-conglycinin respectively. After steam treatment only product Q gave measurable titres; 10 and 11 for glycinin and β-conglycinin respectively.

5. It is concluded that the haemagglutination inhibition assay is a suitable in vitro method of indicating whether soya-bean products given in liquid feeds to preruminant calves will cause gastrointestinal allergic reactions. Furthermore, results show that the removal of deleterious factors from soya-bean meal by treating with ethanol, is critically dependent on the proportion of water present in the ethanol and the temperature of the treatment.

1. The contribution of dietary constituents to the large urinary output of benzoic acid characteristic of ruminants and some herbivores is not well understood.

2. Methods for the analysis of quinic, cyclohexanecarboxylic, benzoic, phenylacetic, 3-phenylpropionic and cinnamic acids in urine and in rumen fluids were developed.

3. The urinary output of aromatic acids by sheep given seven rations was determined: benzoic acid output varied between 2·8 and 7·8 g/d; phenylacetic acid output between 0·16 and 1·3 g/d; cinnamic acid between 0·08 and 0·25 g/d and small amounts of 3-phenylpropionic acid were found in some samples.

4. Increments in urinary aromatic acid excretion were determined when the acids listed in paragraph 2 were infused via rumen or abomasal cannulas.

5. When cyclohexanecarboxylic acid was infused 40% of the dose was excreted as urinary benzoic acid after either route of infusion. Quinic acid was completely metabolized in the rumen: following rumen infusion between 16 and 53% of the infused acid was recovered as urinary benzoic acid; none was so recovered after abomasal infusion.

6. Urinary recoveries of rumen- and abomasally-infused aromatic acids were: benzoic acid 90 and 88% respectively as benzoic acid, phenylacetic acid 78 and 83% respectively as phenylacetic acid, 3-phenylpropionic acid 96 and 105% respectively as benzoic acid and cinnamic acid, 70 and 70% respectively as benzoic acid.

7. The concentration of aromatic acids in rumen fluid varied with time after feeding: cyclohexanecarboxylic acid was maximal (7 mg/l) 1 h after feeding, benzoic acid was always a minor component (0·5 ± 0·5 mg/l), phenylacetic acid varied between 0 and 35 mg/1 and 3-phenylpropionic acid between 25 and 47 mg/l. Cinnamic acid was not found in rumen fluid but on rumen infusion of this acid the concentration of 3-phenylpropionic acid in rumen fluid increased by 10 mg/l rumen fluid per g infused per d.

8. The incomplete metabolism of quinic and cyclohexanecarboxylic acids to urinary benzoic acid is discussed. It is concluded that the principal dietary precursors of urinary benzoic acid in ruminants are compounds yielding 3-phenylpropionic acid on microbial fermentation in the rumen. The small amount of cinnamic acid characteristic of ruminant urine arises as an intermediate in the β-oxidation of 3-phenylpropionic acid in the body tissues.

1. Glucose metabolism and changes in the concentrations of several hormones in jugular plasma were measured in growing lambs fed on fresh pasture ad lib. One group of lambs acted as control while the second received a continuous abomasal infusion supplying 44 g sodium caseinate + 0·5 g L-methionine/d.

2. Hormone concentrations were determined by radioimmunoassay procedures and glucose irreversible loss measured from continuous infusion of D-[U–14C]glucose.

3. Protein infusion increased plasma concentrations of insulin, glucagon and thyroxine (T4), depressed those of growth hormone, prolactin and somatostatin and had no effect on triiodothyronine (T3) concentrations. Cortisol concentrations also tended to be slightly higher in the plasma of protein-infused lambs.

4. Increases in herbage intake within the ad lib. range were associated with increases in plasma insulin and glucagon concentrations and decreases in growth hormone concentration, and it is suggested that these effects could be mediated in part by the accompanying increases in protein absorption from the intestines. The T4:T3 value also decreased with increasing herbage intake, and it is suggested this was due to conversion of T4 to T3.

5. After correction by covariance to equal herbage intake, rates of irreversible glucose loss for control and protein-infused lambs were 9·2 and 10·0 mg/min per kg body-weight0·75. It was calculated that respectively 0·12 and 0·19 of the total glucose production in control and protein-infused lambs could be accounted for by net synthesis from protein.

6. It was concluded that changes in the circulating concentration of several hormones in protein-infused compared with control lambs were likely to have been implicated in protein deposition forming a greater proportion of energy retention in the infused lambs (0·41 v. 0·27).

1. Three diets of barley–canula-seed (Brassica campestiris), lucerne (Medicago sativa) or chopped brome-grass (Bromus inermis) were given at intervals of 3 h to closely-shorn Suffolk wethers held at a temperature of 1–5° (cold) or 22–24° (warm). Apparent digestibility of organic matter (OM) and nitrogen was reduced by 0·08–0·05 and 0·04 units respectively for lucerne and brome-grass diets given to cold-exposed sheep, but no treatment effects on digestibility were observed for the barley–CSM diet. Measurements achieved using infusion of the digesta markers 58Co-EDTA and 103Ru-phenanthroline (103Ru-P) showed that cold exposure depressed apparent OM digestion in the stomach and intestines by 33 and 42 g/d for the lucerne diet, and 13 and 35 g/d for the brome-grass diet respectively.

2. The turnover time (h) of the l03Ru-P marker in the rumen of warm sheep was 38·9 for barley–CSM, 18·4 for lucerne, and 15·6 for brome-grass. In cold-exposed sheep, 103Ru-P turnover time (h) tended to be reduced to 32·3, 12·3 and 15·3 for the three diets, respectively. OM fermentation in the stomach was highly related to 103Ru-P turnover time for lucerne and brome-grass diets.

3. Cold exposure increased the escape of dietary N from the abomasum by 0·04 and 0·09 of dietary N intake for sheep given lucerne and brome-grass diets respectively. Dietary N degradation was closely related to 103Ru-P turnover time for lucerne, and to the proportion of large particles in rumen digesta for the brome-grass diet. Estimates of feed N degradation made by use of information on the rate of fermentation of the diet in nylon bags and 103Ru-P turnover time were consistently lower than those observed in vivo for barley–CSM and lucerne diets. Intestinal digestibility of non-ammonia N was not significantly changed by cold exposure.

4. Transfer of urea from plasma to the rumen was 1·4–2·5 g N/d for the barley–CSM and lucerne diets, but the value for brome-grass was 4·5–4·9 g N/d. Cold exposure did not affect urea transfer. The production of ammonia from feed and endogenous protein was approximately 0·66 and 0·47 g N/g N intake of barley–CSM and lucerne diets, with no effect of cold exposure. Cold exposure reduced the value from 0·57 to 0·38 for brome-grass.

5. The results are compared with those obtained previously with pelleted hay, and the importance of large particle breakdown in the prediction of OM and N fermentation using nylon bags is discussed.

1. The extent to which phenolic derivatives of benzoic acid (seven); of phenylacetic acid (one); of 3-phenylpropionic acid (one) and of cinnamic acid (six) served as precursors of the urinary benzoic acid excreted by sheep was determined after administration as continuous drips via rumen or abomasal cannulas.

2. Phenolic derivatives of benzoic or of phenylacetic acid were not dehydroxylated to yield aromatic acids following administration via either route.

3. Rumen infusion of phenolic derivatives of both 3-phenylpropionic and cinnamic acids gave enhanced rumen concentrations of 3-phenylpropionic acid with negligible amounts of benzoic acid. Between 63 and 106% of the 2-, 3- or 4-hydroxy acids, of the 3,4-dihydroxy acids or of the 3-methoxy, 4-hydroxy acids infused were excreted in the urine as benzoic acid and a variable proportion, characteristic of the individual animal, of up to 20% of the dose as cinnamic acid.

4. Abomasal infusion of monohydroxy 3-phenylpropionic and cinnamic acids did not yield urinary benzoic acid increments. However, between 11 and 34% of abomasally-infused disubstituted phenolic cinnamic acids infused were excreted in the urine as benzoic acid due, it is postulated, to entero-hepatic circulation and microbial metabolism of the infused acids in the large intestine.

5. It is concluded that rumen microbial metabolism of dietary phenolic cinnamic acids to 3-phenylpropionic acid followed by its absorption and oxidation in the body tissues is responsible for the greater part of the benzoic and cinnamic acids found in ruminant urine.

1. The Rumen Simulation Technique (Rusitec) was used in a series of long-term experiments to study the distribution and changes of urease (EC 3.5.1.5) activity in a heterogeneous fermentation system.

2. It was shown that in Rusitec the high urease activity from the inoculum decreased to low values, that the rate of decrease was consistent with simple dilution of ureolytic micro-organisms and that the urease activity could be restored to original values by infusion of urea into the reaction vessels. The magnitude of this urease activity was a direct function of the amounts of urea infused. Single daily additions of the same or greater amounts of urea in food or as solid failed to increase the urease activity significantly.

3. In general, urease activity increased 2–6 h after feeding and the increases were greater with roughage diets.

4. The ureolytic activity per unit volume was always higher in compartment 2 (space occupied by micro-organisms that are loosely associated with the solid) than in compartment 1 (strained rumen contents) or compartment 3 (space occupied by microbial population that cannot be washed out of the solid matrix).

5. The distribution of urease activity between the compartments was different from the distribution of certain other enzymes (e.g. protease and alkaline phosphatase (EC 3.1.3.1)).

6. Apart from the boundary region, the concentrations of urease, ammonia and volatile fatty acids in compartment 2 were constant, while the concentrations of protein, DNA and another enzyme (alkaline phosphatase) increased with the depth of the compartment. Specific urease activity (per unit weight of protein or DNA) was much higher in compartment 1 than in compartment 2 and it decreased markedly with depth of compartment.

7. The concentrations of ammonia were always much higher in the solid matrix (compartments 2 and 3) than in the free suspension of micro-organisms (compartment 1). There was a linear relation between these two quantities.

8. The results are discussed in relation to published work on the entry and metabolism of urea in the rumen.

1. A‘new’carbon radioisotope, 11C, for use in nutritional studies is presented. It has a 20 min half-life, and decays by positron emission giving annihilation photons of 511 keV energy (Wolf & Redvanly. 1977). Thus repeated studies can be made with short time intervals and the distribution of radioactivity in the experimental animal can be detected externally.

2. 11C was produced with a tandem Van de Graaff accelerator and L-[Me-11C]methionine was synthesized and used in model experiments in the pig. The tracer wasadministered intravenously through a catheter in the jugular vein of pigs weighing between 40 and 100 kg. In a series of experiments, one pig received a low-melhionine diet supplemented with DL-methionine to give three different levels of methioninc intake.

3. The radioactivity distribution between liver and muscle was measured as a function of time by external detectors for 2–3 h after administration. Blood and exhaled CO2 were sampled and measured for radioactivity.

4. The results indicate that 11C is a useful radionuclide in nutritional studies in intact large domestic animals.