1. Studies on mineral absorption were carried out in ileostomy patients using the metabolic balance technique. The effect of wheat bran on the absorption of phosphorus, calcium, magnesium, zinc and iron was studied. The extent of digestion of bran phytate in the stomach and small intestine was also investigated.

2. Eight patients with well established conventional ileostomies were studied during two periods while on a constant low-fibre diet. In the second period, 16 g wheat bran/d (American Association of Cereal Chemists) was added to the diet. The amount of phytate-P, non-phytate-P, Ca, Mg, Zn and Fe was determined in the ileostomy contents and in duplicate portions of the diet.

3. Of the added bran phytate-P 24–61% was recovered in the ileostomy contents. In the bran period a significantly decreased amount of Zn was absorbed, while the apparent absorption of Fe and phytate-P increased and that of non-phytate-P, Ca and Mg remained constant. Due to the mineral content of bran, the relative absorption differed in some respects from the absolute absorption, being decreased for Zn, Mg and phytate-P but unchanged for Ca, Fe and non-phytate-P.

4. It is concluded that phytate is partly digested in the stomach and small intestine or possibly absorbed. Addition of 16 g bran/d to the diet does not seem to impair the mineral absorption from the small intestine except that of Zn.

1. Serum prolactin (PRL) levels, both basal and post-suckling peak, were estimated in fifty-seven lactating women.

2. Basal PRL levels were significantly higher in all lactating women irrespective of the duration of lactation as compared to the levels in non-pregnant, non-lactating women.

3. There was a significant positive correlation (r 0·69, P < 0·001) between the basal PRL levels and the post-suckling peak values.

4. After 8 months of lactation, peak post-suckling, PRL levels were not significantly different from basal values.

5. Basal PRL levels were significantly lower (P < 0·05) in mothers whose infants were being supplemented.

6. PRL levels were not related to the mother's nutritional status as determined by body-weight.

7. The findings suggest that high PRL levels during lactation prolong the duration of lactional amenorrhoea and hence the relative infertility.

1. Breast milk samples were collected from mothers living in areas having an average of 0.2 and 1.7 μg fluorine/ml in drinking water. The samples were analysed for their ionic and total F concentrations.

2. Ionic F was determined after microdiffusion by the fluoride-selective electrode. For total F determinations, milk samples were ashed with magnesium succinate fixative, after which the F concentration was determined as mentioned previously.

3. The median totals for F content of breast milk in the low- and high-F areas were 7.0 ng/ml (range 4.3–14.0 ng/ml, fifteen mothers) and 10.9 ng/ml (range 4.5–50.7 ng/ml, nine mothers). The median ionic F concentrations were 5.0 ng/ml (range 3.0–6.3 ng/ml, fifteen mothers) and 8.9 ng/ml (range < 2.0–39.9 ng/ml, nine mothers) respectively. Both the total F (0.01 > P > 0.001) and ionic F (0.05 > P > 0.01) in breast milk were significantly higher in the high-F area compared to the low-F area.

4. At the ages of 1, 2 and 3 months, the calculated average total daily F intakes of exclusively breast-fed infants were 4.8 and 7.3 μg; 5.0 and 7.8 μg; 5.4 and 8.5 μg in the low- and high-F areas respectively.

1. The activity of manganese-superoxide dismutase (EC 1.15.1; SOD) was increased in the livers and kidneys of adult rats after exposure to aqueous ethanol (200 ml/l) for 32 weeks.

2. The concentration of Mn in the livers and kidneys was significantly higher after 24 weeks, and by 32 weeks liver copper and zinc levels were lower.

3. The activity of foetal (day 19) liver superoxide dismutase was appreciably higher in offspring from dams receiving ethanol during pregnancy. Quantitatively the response appeared to be almost entirely due to the Mn-SOD form of the enzyme.

4. Maternal alcoholism during pregnancy had no effect on the levels of Cu, Mn or Zn in foetal (day 19) livers.

1. The effect of variation in arginine: lysine on the relative cholesterolaemic effects of dietary soya-bean protein and casein was studied. Male rats received semi-purified diets containing soya-bean protein isolate or casein supplemented respectively with varingamounts of lysine or arginine for 40 d and blood samples were taken after a 5 h fast.

2. Neither the addition of arginine to casein nor lysine to soya-bean protein modifiedthe intrinsic effect of these proteins on serum cholesterol.

3. Serum triglyceride levels tended to rise with increasing amounts of lysine supplementation. The opposite trend was obtained with arginine supplementation.

4. Casein caused an increase in the concentration of serum insulin, but not glucagon. The glucagon level was increased proportionately with increasing amounts of arginine, while the addition of lysine showed no effect. The effects of added amino acids on serum insulin were inconclusive.

5. There was a parallel increase in serum apo E and glucagon in response to arginine supplementation, while lysine supplementation increased serum apo E.

6. Thus, arginine:lysine was more effective in regulating serum triglyceride than serum cholesterol. Insulin was associated with different effects of these proteins on serum lipids.

1. During a period of 2 years, every 2 months 126 different food items forming a 'market basket' were purchased, prepared and divided into twelve food commodity groups. The 'market basket' was based on a study of the dietary pattern of 16- to 18-year-old male adolescents. In the (homogenized) food groups various additives and components of nutritional importance were determined. From the concentrations of the additives and components in the food groups and the daily consumption of each food group, a mean daily intake of all components analysed was calculated.

2. The mean daily amounts of benzoic acid (34 mg), sorbic acid (6 mg), glutamic acid (66 mg) and sulphite (3 mg) were all far below the acceptable daily intake (ADI) value. Butylated hydroxytoluene and gallates were not detectabte, while bulylated hydroxyanisole (BHA) was found in only a few instances; the maximum amount of BHA was also very iow (4 mg).

3. The mean daily intakes of fluorine (0.8 mg), iodine (0.21 mg), phosphorus (1860 mg) and α-tocopherol (9.4 mg) seem safe and adequate. Cholesterol intakes of 25% above the maximum of 300 mg/d, as advised by the Dutch Bureau for Nutriiion Education, were found. The mean fat intake appeared to be 40% of total daily energy, protein content 13% of total energy and total (available) carbohydrate 46% of total energy. The daily dietary fibre content (18 g) and the daily amount of linoleic + Iinolenic acid (6% of total energy) were considered too low. The daily level of sodium (4.2 g) was not considered too high.

4. It is recommended that the study should be repeated regularly, e.g. every few years, in order to monitor trends in the concentrations of significant food components in total diets.

1. Behavioural responses of young anaemic Indian children to iron-folic acid supplements were assessed in two separate studies using the Indian adaptation of Wechsler's (1967) intelligence scale for children (WISC).

2. The first study was an exploratory study in which the cognitive behaviour of 5–8-year-old children of both sexes was assessed before and after supplementation with 20 mg elemental Fe and 0.1 mg folic acid given daily for a period of 60 d.

3. The supplemented children showed a significant improvement in haemoglobin (Hb) as well as the WISC scores while the control children who did not receive any supplements failed to show an improvement either in Hb or in the WISC scores. However, within the supplemented group when the initially-anaemic children were compared with the inttially-non-anaemic ones, only the 7-year-old anaemic children performed significantly poorer in the tests than the non-anaemic group of the same age. The study raised the possibility that in addition to increasing the blood Hb levels, Fe-folic acid supplements may have additional benefits in improving the cognitive performance of children.

4. In the second study, cognitive behaviour of fourteen matched pairs of anaemic children in the age-range of 5–6 years was assessed before and after supplementation with 40 mg Fe and 0.2 mg folic acid given daily in two divided doses or sugar placebos for a period of 60 d. The tester did not know the group to which each child belonged.

5. The supplemented children showed a significant improvement in Hb as well as in the verbal and performance IQ of WISC. The control children showed no improvement in Hb but their verbal IQ improved significantly. However, there was no significant improvement in their performance IQ.

6. The results indicated that Fe-folic acid supplements to anaemic children not only raised Hb levels but also improved intelligence test results, particularly in the performance section.

1. Energy, protein, zinc, copper, manganese, selenium and dietary fibre intakes of 100 pre-menopausal women (mean age 30·0 ± 6·1 years) from a university community, and consuming self-selected diets, were calculated using 3 d dietary records and food composition values. Subjects also collected a 24 h food composite during the 3 d record period for analysis of Zn, Cu and Mn by atomic absorption spectrophotometry. Daily analysed intakes were compared with those calculated from the corresponding record day.

2. Mean daily calculated intakes of energy, protein, Zn, Cu, Mn, Se and dietary fibre were 7·54 ± 1·61 MJ, 74 ± 18 g protein, 10·1 ± 3·3 mg Zn. l·9 ± 0·6 mg Cu, 3·1 ± 1·5 mg Mn, 131 ± 53 μg Se, 19·4 ± 6·6 g dietary fibre.

3. Major food sources for each of the trace elements were (%): Zn meat + substitutes 43, dairy products 23·7; Cu breads and cereals 22, vegetables 21; Mn breads and cereals 47, fruits 12; Se meat + substitutes 38, breads and cereals 30.

4. Highly significant correlations (P = 0·001) were noted for analysed intakes of Zn, Cu and Mn and those calculated from the corresponding record day. Mean calculated intakes were higher (%): Zn 138, Cu 142, Mn 121, than corresponding mean analysed intakes (P = 0·01). However, the mean nutrient densities (mg/MJ) were comparable: Zn analysed 1·2, calculated 1·4; Cu analysed 0·2, calculated 0·2; Mn analysed 0·4, calculated 0·4.

5. All subjects met the Canadian Dietary Standard (CDS) recommended level for Cu but 48% received less than the CDS for Zn, 6% obtaining less than two-thirds of this recommended level. Daily Mn and Se intakes were similar to recent values for North American diets.

1. Three sheep fitted with rumen and oesophageal cannulas were given hourly the following diets in successive experiments: 1000 g pelleted-grass cubes/d (diet A) and 700 g pelleted-grass cubes plus 300 g flaked barley/d (diet B).

2.During the final week of each 4-week dietary regimen, a balance trial was conducted and on separate days each sheep was continuously infused with [14C]urea and NaH14CO3 intravenously and NaH14CO3 intraruminaily. C transfer rates between blood urea, blood bicarbonate and rumen bicarbonate pools were calculated from the specific radioactivity of urea and bicarbonate sampled and isotope infusion rate during each experimental period. In the same period, an oral infusion of 51Cr-EDTA was maintained and salivary flow rate and composition determined from samples collected from the oesophageal fistula.

3. The inclusion of flaked barley in the pelleted-grass diet significantly (P < 0·01) increased the apparent digestibility of organic matter (0·069), apparently digestible organic matter intake and nitrogen balance, and increased the efficiency cf dietary N utilization from 0·059 (diet A) to 0·290 (diet B). Increased N balance was the result of a significant (P) < 0·01 reduction in urinary urea excretion.

4. The rumen fluid of sheep given diet A had higher pH and bicarbonate concentrations but lower butyric acid concentrations than that of sheep given diet B. There was no significant effect of diet on total volatile fatty-acid or ammonia concentrations in rumen fluid, or on osmolaiity and rumen fluid dilution rate. The irreversible loss of bicarbonate from rumen fluid was markedly increased when flaked barley was included in the diet, with most of the loss occurring directly from rumen fluid.

5. Sheep given diet A had higher salivary secretion rates (18·8 l/d) than those given diet B (12·7 l/d), and with the exception of urea, there was no effect of diet on the concentrations of total N, protein N, alpha;-amino-N, uric acid-N or bicarbonate in saliva. Urea concentrations in saliva were significantly correlated (r20·64) with blood urea concentrations, but not with salivary flow rate. Salivary secretions contributed 2·2 and 1·4 gN/d to the rumen of sheep given diets A and B respectively, with urea forming only 45–33% of the total N secreted.

6. When flaked barley was included in the pelleted-grass diet, there was a significant (P < 0·01) decrease in urea synthesis rate (diet A 20·0 g N/d, diet B 9·7 g N/d), a significant increase in amount (diet A 2·3 g N/d. diet B 3·0 g N/d) and proportion (diet A 0·024, diet B 0·57) of recycled urea degraded in the rumen. The permeability of the rumen wall to urea was also significantly increased in sheep given the flaked barley diet (diet A 1·35 g N/d, diet B 2·45 g N/d).

7. A model of urea metabolism in sheep given each diet is described, and the mechanisms by which flaked barley inclusion increased urea recycling to the rumen and the efficiency of dietary N utilization are discussed.

1. Three sheep fitted with rumen cannulas were fed hourly a daily ration of 1000 g pelleted-grass cubes, and during four successive 2-week periods were intraruminally infused (0·45 l/d) with solutions containing sodium chloride (0·47 mol/d), sodium bicarbonate (0·47 mol/d), ammonium chloride (0·47 mol/d) and sodium butyrate (0·47 mol/d). Each solution, except that for NaHCO3, was adjusted to pH 7 before infusion, and provided equal sodium intakes for sheep in all periods.

2. In the final week of each infusion period, a balance trial was conducted and on separate days each sheep was continuously infused with [14C]urea and NaH14CO3 intravenously and NaH14CO3 intraruminally. Carbon transfer rates between blood urea, blood bicarbonate and rumen fluid bicarbonate were calculated from the specific radioactivity of urea and bicarbonate samples and isotope infusion rates during each experimental period.

3. There was no significant effect of intraruminal infusions on N balance, and with the exception of sheep in fused with NH4Cl, all sheep utilized apparently digested N with similar efficiency for N retention. Sheep infused with NH4Cl (6·2 g N/d) excreted the equivalent of 93% of the infused N as urea in urine.

4. Infusion of NaHCO3. NH4Cl and sodium butyrate significantly (P < 0·05) increased the rurnen fluid concentrations of bicarbonate, ammonia and butyric acid respectively, and all infusions significantly (P < 0·05) increased total volatile fatty acid concentrations. Both NaHCO3 and sodium, butyrate significantly (P < 0·05) increased the pH of rumen fluid There was no significant effect of infusion on the proportions of propionic acid or the osmolality of rumen fluid.

5. Intraruminal infusions of NH4Cl significantly (P < 0·05) increased and infusion of sodium butyrate significantly (P < 0·05) decreased plasma urea concentrations. Sheep infused with NH4Cl had higher rates of urea synthesis and urinary urea excretion compared with sheep on the other treatments, and a significantly (P < 0·05) lower proportion of urea synthesized by these sheep was degraded in the digestive tract. Sheep infused with sodium butyrate degraded a significantly (P < 0·05) greater amount (3·2 g N/d) and proportion (0·24) of total urea synthesis in the rumen than did sheep infused with NaCl. Corresponding values for the control (NaCl) sheep were 1·5 g N/d and 0·13 respectively. There was no significant effect of other infusions on the amount of urea recycled to the rumen or on the distribution of total urea degradation between the rumen and lower digestive tract. Plasma urea clearance to the rumen was significantly (P < 0·05) increased during sodium butyrate infusion, and the clearance of urea to the lower digestive tract was significantly (P < 0·05) decreased during NH4Cl infusion.

6. The mechanism by which urea entry into the rumen is regulated by rumen metabolite levels is discussed.

1. Glucosyl urea, lactosyl urea and galactosyl urea were prepared from pure sugars and urea and their purity confirmed by determination of their melting points, specific rotations and by mass spectrometry.

2. Using whey as a lactose source, a range of conditions were examined for the preparation of lactosyl urea on a laboratory scale. Yields of 60% were achieved when lactose and urea (molar ratio, urea: lactose 0:6) were reacted for 15 h in sulphuric acid at pH 2·0 and a temperature of 70°.

3. Methods of detection and estimation of all three ureides in whey preparations and ruminant digesta samples were developed. Two quantitative methods, one involving acid-hydrolysis, the other ion-exchange chromatography, were used. The latter method enabled determination of individual quantities of ureides in mixtures.

1. The fate of glucosyl urea (GU), lactosyl urea (LU) and corresponding mixtures of the free sugars and urea and their degradation products were examined during in vitro incubation of the compounds with rumen contents taken from donor sheep and steers at various stages of adaptation to these compounds.

2. The sugar–urea bond was virtually unattacked in rumen contents from unadapted sheep and steers but generally a slow release of the galactose moiety occurred. After feeding LU or GU to animals for a period of approximately 10 d, the rates of disappearance of both bound urea and sugar had increased, but were still markedly slower than those of the corresponding free sugars and urea. In vitro rates of degradation of both free lactose and urea also increased in response to the feeding of lactose and urea to rumen contentdonor animals.

3. Ammonia accumulation in rument contents when GU or LU were the substrates was notably lower than when equivalent amounts of glucose and urea or lactose and urea were the substrates.

4. Bacterial growth was estimated using an vitro method based on incorporation of 32P into bacterial nucleic acids. Markedly different patterns of bacterial growth were observed depending on whether LU or lactose and urea were the substrates.

1. Steers and sheep were given basal diets of barley and straw (1:1. w/w), usually containing urea, which for certain experimental periods were supplemented with pure glucosyl urea (GU), pure lactosyl urea (LU) or a product prepared from whey concentrate (EW) which contained 65–80% of the lactose in the form of LU.

2. On the morning of an experiment ureide (or EW) was omitted from the feed and a dose of either ureide (or EW) or equivalent amounts of free lactose and urea (L+U) was added to the rumen within 30 min of feeding, together in some experiments with polyethylene glycol (PEG) as a fluid-phase marker. Samples of rumen contents, and in some experiments abomasai contents, were taken at intervals for up to 8 h.

3. For both steers and sheep given GU and LU for the first time (unadapted animals) there was little or no accumulation of ammonia in the rumen or cleavage of the sugar-urea bond. Galactose was. however, slowly liberated from LU.

4. For steers and sheep which had been given GU, LU or EW for approximately 7–10 d or more (adapted animals) some accumulation of ammonia occurred after adding GU or LU to the rumen, but for LU it occurred less rapidly and to a lower peak concentration than when L + U was added. In adapted animals cleavage of the sugar-urea bond in LU was virtually complete in 2–4 h. Degradation of the components of L + U was virtually complete within 1 h.

5. Recovery at the abomasum of ureide (present either as GU or LU) estimated from ureide: PEG values, appeared to be complete in experiments with unadapted sheep given a dose of EW. In adapted sheep only very small amounts of ureide in an EW dose (on average 6%) entered the abomasum undegraded. Amounts lost in this way appeared to be positively correlated with the rate of fluid turnover in the rumen.

1. The metabolism of acetate, glucose and D(−)-3-hydroxybutyrate was studied in lactating and non lactating sheep in vivo. Special consideration was given to the utilization by hind-limb muscle in both groups of sheep and the uptake of nutrients by the lactating mammary gland was also measured.

2. The entry of acetate into the circulation (mmol/h per kg body-weight) was similar in all experimental animals at a given arterial concentration of acetate. However, normal lactation was associated with a reduced extraction of acetate by muscle and the 'spared' acetate was comparable with that removed by the udder. Feeding lactating ewes a 700 g concentrate/kg ration tended to prevent this redistribution of acetate utilization.

3. The muscle of non-lactating ewes utilized sufficient glucose, when corrected for lactate release, to account for 57% of the oxygen utilization by muscle. In lactation this fell to 32%, largely because of an increased lactate production. D(−)-3-Hydroxybutyrate utilization by muscle accounted for 16–17% of the O2 consumed by the muscle in non-lactating and lactating sheep.

4. Lactating mammary gland metabolism in sheep was similar to published values for dairy cows and goals. Thus the extraction (%) of glucose, O2, acetate and D(−)-3-hydroxybutyrate was 25, 28, 62 and 53 respectively. Blood flow was 529 ml/min per kg udder and the ratio blood flow: milk flow was 475. Glucose used by the udder relative to the whole animal utilization rate may be less in sheep than in cows and goats, but the comparable proportion for acetate is as large or larger than in these species.

1. Digesta passage and retention were measured in heifers, sheep, goats, equines and rabbits of varying body-weights when given timothy (Phleum pratense) hay.

2. Two passage markers were compared, cobalt (III) ethylene diamine tetraacetate (CoEDTA) and chromiummordanted timothy fibre for liquid and solid phase respectively. Both markers were injected into the rumen of the ruminants and into the caecum of the equines andrabbits.

3. In ruminants, two different sets of rate constants (k1 and k2) were derived from a two-pool model for marker passage, using a graphical approach and a computer-based non-linear least-squares curve-fitting technique.

4. Retention times, due to unidirectional flow through the gastrointestinal tract (transit time) and due to pool effects (mean retention time, MRT), were calculated.

5. Curve fitting was only successful for the excretion of liquids in ruminants. The two-pool model was not applicable to the passage of solids.

6. Apparent retention of liquid was always shorter than for solids in all species, except in rabbits. However absorption of CoEDTA was too large in the rabbits to determine liquid retention accurately. Times for first appearance of the two markers were similar within animal groups.

7. MRT values were lowest in the rabbit, intermediate in equines and high in the ruminants. The MRT values (h) of solids and liquid respectively were: large heifers 65, 18; small heifers 48, 20; goats 41, 28: sheep 57, 26: equines 23, 18; rabbits 5·3, not determined.

8. Liquid retention seemed to decrease somewhat with increasing body-weight in the ruminants. Solids retention decreased with decreasing body-weight in the ruminants, but sheep had longer retention times than goats of similar size. Equines exhibited large individual variation in retention of the liquid or solid markers, seemingly unrelated to size. Noeffect of size was seen in the retention of solids in the rabbits.

1. Q-strain mice selected for high-line (QLF) or low-line (QSC) body-weights at 6 weeks of age were culled to litters of two or eight (QLF-2, QLF-8, QSC-2, QSC-8) at birth andwere suckled in these groups until 19 d of age.

2. Body-weights were measured daily for all groups and body compositions compared at birth and 19 and 42 d of age. Food intakes and urinary and faecal nitrogen were measured during metabolism trials between 19 and 42 d.

3. QLF-2 and QSC-2 mice grew faster than the corresponding groups of eight until 19 d of age. They also deposited more fat as a percentage of total gain.

4. In the period 19–42 d the influence of genetic selection reappeared and was manifest in a slowing of growth rates of QLF-2 and QSC-2 animals so that by 42 d of age therewere no differences in body-weight between the groups within a line.

5. During the period 19–42 d the total food intakes of each group within a line did not differ although, on the basis of food intake per unit metabolic body-weight (g/kg body-weight0.75 per d) QLF-2 and QSC-2 ate less food than QLF-8 and QSC-8respectively.

6. The differences in body-weight at 19 d between groups were largely overcome by the increased contribution of protein and water to the weight gain of the groups of eight duringthe post-weaning period.

1. Male WAG/Cpb inbred rats fed on rations containing 1·5 mg copper/kg (deficient) and 6·0 mg Cu/kg (adequate) were supplemented with molybdenum (500 mg/kg diet). Starting at week 0 rats were killed weekly for up to 6 weeks and the caeruloplasmin activity of plasma, the Cu concentration of plasma, liver and kidney and the Mo concentration of liver and kidney were determined. The experiment was repeated with rats fed on diets of the same composition but given additional Cu for periods of 2 weeks. Cu was given orally by increasing dietary Cu to 6·0 mg/kg and 25·0 mg/kg for Cu-deficient and Cu-adequate rats respectively or intraperitoneally by injecting 75 μg and 250 μg every second day to Cu-deficient and Cu-adequate rats respectively.

2. After Mo administration to Cu-deficient rats plasma and kidney Cu and liver and kidney Mo increased but caeruloplasmin activity and liver Cu decreased. In Cu-adequate rats plasma, liver and kidney Cu and liver and kidney Mo increased to much higher levels than in Cu-deficient rats. Caeruloplasmin activity was not affected. Fluctuations in plasma Cu and kidney Mo were correlated closely.

3. No qualitative difference between the effect of oral or intraperitoneal Cu administered to Mo-treated Cu-deficient or Cu-adequate rats was found. In Cu-deficient Mo-supplemented rats additional Cu increased plasma Cu, caeruloplasmin activity and liver and kidney Cu and Mo. In Cu-adequate Mo-supplemented rats additional Cu decreased plasma Cu and liver and kidney Mo and increased caeruioplasmin activity and kidney Cu and, to a minor extent, liver Cu.

4. In view of the assumption that in rats a Cu, Mo and S containing compound, related to Cu-thiomolybdate, may be formed in vivo the results suggest thai Cu binds to the Mo-S part of the compound; when this compound is formed in the gastro-intestinal tract it can not be absorbed and when it is formed at systemic sites it changes the Cu distribution.

1. The effects of three levels of linseed oil (LSO) supplementation of a basal diet on rumen digestion and flow of nutrients to the proximal duodenum of three mature sheep provided with permanent rumen and duodenal re-entrant cannulas were studied.

2. A basal diet of 200 g hay and 400 g concentrates daily, providing approximately 7.0 MJ digestible energy and 13 g N/d, was given alone or with supplements of 13, 26 or 40 ml LSO/d in two equal portions at 06.00 and 18.00 hours. The flow of duodenal digesta was measured by spot-sampling using chromic oxide paper as the marker. Bacterial protein synthesis (BPS) was measured by the diaminopimelic acid technique.

3. Addition of LSO reduced the digestion of energy and organic matter, particularly acid-detergent fibre, in the stomach. Digestion in the intestines increased but at the higher levels of supplementation this failed to compensate completely for the reduction in rumen digestion. Total volatile fatty acid concentrations were not affected but molar proportions of acetate and butyrate were decreased by approximately 18 and 61% respectively while the molar proportion of propionate was increased twofold by the highest concentration of oil. The higher concentrations of LSO virtually eliminated protozoa from the rumen.

4. The second increment of LSO (26 ml/d) produced the highest duodenal flow of total N and bacterial N and the highest efficiency of BPS. The highest concentration of oil (40 ml/d) was without effect. Rumen and duodenal ammonia concentrations and plasma urea concentrations tended to be reduced by the higher concentrations of LSO.

5. It is argued that the results support suggestions made elsewhere that free oils reduce the efficiency of BPS but that they also reduce the numbers of protozoa which can cause an increase in the efficiency of BPS. The net effect of free oil supplementation on BPS is thus likely to be variable and difficult to predict.

1. Six sheep, each fitted with a rumen cannula and re-entrant cannulas in the proximal duodenum and distal ileum, were given two diets (600 g dry matter (DM)/d) consisting of either grass silage (32·1 g nitrogen/kg DM) or dried grass (18·3 g N/kg DM). A net loss of N occurred between mouth and duodenum with the silage diet, indicating extensive ruminal degradation of dietary N, compared with a net gain on the dried-grass diet. Consequently, despite higher N intakes when silage was given, N flow at the duodenum was similar for both diets.

2. The proportion of microbial N in duodenal digesta N was estimated using diaminopimelic acid (DAPA), [35S]methionine (35S), 15N-enriched non-ammonia-N (15NAN) and amino acid profiles (AAP) as microbial markers. Isotopic labelling of rumen micro-organisms was achieved by intraruminal infusions of Na235SO4 and (15NH4)2SO4.

3. A comparison of all methods was made based on the marker concentrations in microbial fractions isolated by differential centrifuagation of strained rumen contents. With both diets, DAPA gave the highest estimates and AAP the lowest. Estimates based on 35S and 15NAN were intermediate and did not differ significantly (P > 0·05).

4. For the 15NAN, 35S and AAP methods, the effect of site of sampling of the microbial fraction, i.e. from rumen contents or duodenal digesta, was examined and in all instances mean estimates based on duodenally-derived microbes were higher. However, the differences were significant for only 15NAN with both diets (P < 0·001), for 35S with the dried grass (P < 0·05), and for AAP with the silage (P < 0·05). Estimates based on duodenally-derived microbes were higher (P < 0·05) using 15NAN than those obtained using 35S with both diets.

5. Depending on the method used for estimating microbial N, estimates of the efficieny ofmicrobial N synthesis in the rumen (g microbial N flow at duodenum/kg organic matter apparently digested in the rumen) ranged between 16 and 38 for the silage diet and 10 and46 for the dried grass diet. Similarly, estimates of feed N degradability in the rumen ranged between 0·62 and 0·97 for the silage and 0·00 and 0·93 for the dried grass.