The amino acid composition of the protein from three strains of rat (Wistar, Zucker lean and Zucker obese), subjected to reference and high-fat diets has been used to determine the mean empirical formula, molecular weight and N content of whole-rat protein. The combined whole protein of the rat was uniform for the six experimental groups, containing an estimate of 17.3% N and a mean aminoacyl residue molecular weight of 103.7. This suggests that the appropriate protein factor for the calculation of rat protein from its N content should be 5.77 instead of the classical 6.25. In addition, an estimate of the size of the non-protein N mass in the whole rat gave a figure in the range of 5.5 % of all N. The combination of the two calculations gives a protein factor of 5.5 for the conversion of total N into rat protein.

In order to determine the extent to which the concentration of albumin in plasma is maintained at the expense of the extravascular pool during protein-energy malnutrition, the rates of exchange between albumin in plasma (1A) and the extravascular pool (EA) and consequently the distribution of albumin between intravascular and extravascular pools (expressed as EA:IA) were measured in protein-energy-depleted and control rabbits. The fractional rates of synthesis (FSR) and catabolism (FCR), the concentration of albumin and the plasma volume (PV) were also measured. In animals in which protein-energy intake was reduced by 58% the concentration of albumin in plasma remained unchanged, whereas FCR decreased by 38 % and FSR by 30 YO. No significant changes in EA: IA or PV were found. We conclude that albumin concentration during proteirrenergy depletion is not maintained at the expense of extravascular albumin, but by parallel changes in the rates of catabolism and synthesis.

In a cohort (n 81) of healthy children aged 1.5–4.5 years, measurements of energy intake and energy expenditure were compared. Energy intake was calculated following a 4 d weighed record completed by the mother or guardian of the child. Total energy expenditure was measured using the doubly-labelled water technique. Mean energy intake and expenditure in the cohort were 4773 kJ/d and 4928 kJ/d respectively. The mean relative bias between the techniques was 154 kJ/d. In the older children (3.5–4.5 years) the mean relative bias was only 37 kJ/d. At the population level the measurements of energy intake and energy expenditure were extremely close, and the study has provided sufficient confidence in weighed intake methodology for it to be used in a major nationwide study of dietary intake and nutritional status of children aged 1.5–4.5 years.

The effects of severe protein restriction following parturition on the changes in rat milk composition during lactation were investigated using multiparous female Sprague-Dawley rats caged individually following mating and offered a high-protein diet (H; 215 g crude protein (N × 6·25; CP)/kg dry matter (DM)) ad lib. until parturition. Following parturition, half the females continued to receive diet H, whilst the remainder were offered a diet low in protein (L; 90 g CP/kg DM) ad lib. On days 2, 4, 8 and 12 of lactation groups of females from both dietary treatments were used to provide a milk sample. Milk samples were analysed for their lactose (enzymically), protein (binding to Coomassie blue), lipid (gravimetrically) and mineral (spectrophotometrically) contents. The milk lactose concentration of group H increased with stage of lactation (r2 0·85, P < 0·001). Such an increase was prevented by diet L, and from day 8 of lactation the milk lactose of group L was lower (P < 0·05) than in group H. Group H milk protein concentration did not change during lactation and averaged 90·7 mg/g. Dietary protein restriction reduced the milk protein concentration of group L so that on days 2, 4 and 12 of lactation it was lower (P < 0·05) than that of group H. On day 8 of lactation the milk protein concentration of group L had increased (P < 0·05) and was comparable with that of group H. For group H, milk lipid averaged 166·8 mg/g and was generally unchanged during lactation. Diet L increased (P < 0·01) the milk lipid concentration (205·5 mg/g) compared with diet H and this was also significant on days 4 and 8 of lactation (P < 0·05). Group L milk lipid concentration also increased between days 4 and 8 of lactation (P < 0·05). Milk Na concentration declined during lactation in both dietary groups (P < 0·01) but was unaffected by dietary treatment. Both milk Ca and P concentrations increased (P < 0·01) during lactation in both dietary groups, whilst protein restriction also increased the Ca and P concentrations (P < 0·05). Milk K and Mg concentrations were unaffected by dietary treatment or stage of lactation. This significant alteration in the milk composition of severely protein-restricted dams, while possibly favouring the disposal of greater quantities of energy-yielding nutrients, suggests that equations developed for the estimation of milk production in rats cannot be used under such conditions. Laction: Milk composition: Feed intake: Dietary protien: Rat

This study investigates the mechanisms of action for the hypocholesterolaemic effects of sugar-beet fibre (SBF) and gum gum. Four groups of ten male Wistar rats were fed ad lib. on test diets containing either 100 g SBF or guar/kg, or control diets containing 100 g cellulose or wheat bran/kg for 28 d. Food intake, weight gain and food consumption ratios were unaffected by the diets. Circulating cholesterol and hepatic cholesterol concentrations were significantly lower in both SBF- and guar-fed groups compared with either cellulose- or bran-fed animals. Circulating triacylglycerol concentrations were significantly lower in SBF- and guar-fed animals, but total hepatic lipid concentrations and hepatic and adipose tissue lipogenesis rates were unaffected by the diets. Hepatic cholesterol-7α-hydroxylase (EC1.14.13.17) activities were significantly higher in the guar-fed animals compared with cellulose or bran control groups. Hepatic 3-hydroxy-3-metbylglutaryl-CoA reductase (EC1.1.1.88) activities were unaffected. Circulating bile acid concentrations were significantly lower in SBF- and guar-fed animals and faecal bile acid output was significantly higher in the guar-fed group compared with bran- or cellulose-fed groups. This study supports the hypothesis that guar exerts its hypocholesterolaemic effect via intraluminal bile acid binding and loss of cholesterol from increased faecal bile acid excretion. The mechanism of action for the hypocholesterolaemic effect of SBF is less clear; the results of the present study point to a mechanism involving disruption of the enterohepatic bile acid circulation, possibly via changes in the rate of absorption of dietary lipid.

The present study was undertaken to investigate the changes in muscle protein turnover involved in the rapid mobilization of protein in rats subjected to severe protein restriction during lactation. Estimates of mammary gland and liver protein synthesis were also made during lactation. Multiparous female Sprague-Dawley rats, caged individually following mating, were offered a high-protein diet (H; 215 g crude protein (N - 6·25; CP)/kg dry matter (DM)) ad lib. until parturition. Following parturition, half the females continued to receive diet H, whilst the remainder were offered a diet low in protein (L; 90 g CP/kg DM) ad lib. On days 2, 4, 8 and 12 of lactation, groups of females were used in the estimation of tissue protein synthesis (flooding dose of [3H]phenylalanine) immediately after a milk sample had been obtained. Rates of muscle protein synthesis were unchanged during lactation in group H. The feeding of diet L during lactation reduced the muscle protein synthesis on day 12 to rates that were lower than group H and also the rate on diet L on day 2 (P 0·01). However, this fall in muscle protein synthesis was not rapid and muscle fractional synthesis rate (FSR) was different from group H only from day 8 (P 0·05). Estimated rates of mammary protein synthesis appeared to be generally unchanged by dietary treatment or stage of lactation. Liver FSR was also unchanged by dietary protein supply or stage of lactation. The effect of dietary protein restriction on liver size and protein content during lactation influenced liver absolute synthesis rate (ASR), and on days 8 and 12 of lactation liver ASR was lower in group L than in group H (P 0·001). The loss of muscle protein in rats fed on diet L during lactation (133 mg) occurred mainly between days 2 and 8 of lactation and was primarily associated with a dramatic increase in degradation (13·0% per d), with the decline in synthesis having a much smaller role. A decline in muscle protein degradation during the latter half of lactation was part of the mechanism that prevented excessive muscle protein catabolism. It is thought that the estimation of mammary protein synthesis in the present study was impaired by the milk sampling procedure previously used.

The doubly-labelled water (2H218O) technique was used to assess the long-term rates of energy expenditure and, after accounting for any changes in body composition, the derived rates of energy intake in weight-stable ‘large-eating’ (n 6) and ‘small-eating’ (n 6) women. The self-reported energy intakes (approximately 11.2 v. 5.6 MJ/d) and energy expenditures (approximately 8.5 v. 12.4 MJ/d) for the ‘large-eating’ and ‘small-eating’ groups respectively, should not be sustainable without significant body-weight changes. 2H218O-assessed rates of energy expenditure for the ‘large-eaters’ (approximately 8.5 MJ/d) and ‘small-eaters’ (approximately 11.3 MJ/d) were in close agreement with the results obtained using 5 d, self-reported activity diaries but the derived rates of energy intake for the ‘large-’ (approximately 8.5 MJ/d) and ‘small-eaters’ (approximately 10.8 MJ/d) were markedly different from those obtained using self-reported, weighed food diaries. When two ‘small-eaters’ were supplied with their self-reported energy intakes (approximately 5 MJ/d) for up to 28 d both subjects lost about 0.75 kg body-weight/week. These results provide no support for the existence of ‘metabolically efficient’ women in the community.

The kinetics of blood free amino acids (AA) transfer into milk casein were compared in goats (n 4) at 61 (SE5)d (Expt 1; post-peak, 4.51 (SE 0.26) kg milk/d) and at 180 (SE 6) d (Expt 2; late, 2.36 (SE 0.16) kg milk/d) of lactation during non-primed, continuous (Expt 1, 12 h; Expt 2, 16 h) intravenous infusions of mixtures of L-[1-13C]leucine and L-[1-13C]phenylalanine with either L-[1-13C]valine (Expt 1) or L-[5-13Cmethionine (Expt 2). The 13C enrichments of blood free and casein-bound AA were fitted to a single exponential model to estimate isotopic plateaux and the fractional rate constant for milk casein labelling. Milk protein output and its contribution to whole-body flux was higher in Expt 1 (post-peak) than in Expt 2 (late lactation), but the kinetics of 13C labelling of the casein-bound AA were similar for all AA tracers in both experiments. At both stages of lactation the delay (6–8 h) between the attainment of isotopic plateau for the blood free AA and the corresponding attainment of plateau for the casein-bound AA indicated that the blood free pool was not the immediate precursor pool for milk casein biosynthesis. Plateau enrichments of casein-bound AA were generally higher than those for the corresponding blood free AA in both experiments. These results indicate that the relative contributions of different AA sources to the immediate precursor pool for milk casein biosynthesis are similar at different stages of lactation despite major changes in the partitioning of whole-body flux towards milk protein output. Non-milk protein fluxes were also similar in post-peak and late lactation.

Fifteen sheep (53 kg), with catheters in a hepatic vein, the portal vein and a mesenteric vein and artery, were offered a bromegrass (Bromus inermis) hay (104 g crude protein (CP), 700 g neutral-detergent fibre and 65 g acid-detergent lignin/kg dry matter (DM)) ad lib. with different supplements to determine the effects on net flux of oxygen and nutrients across the portal-drained viscera (PDV) and liver. The sheep were unsupplemented (Control) or received 5 g DM/kg body weight (BW) of ground maize (M), 7 g DM/kg BW of soya-bean hulls (H) or 0.73 g DM/kg BW of a mix of feedstuffs high in rumen-undegradable protein (P). Apparent digestible energy (DE) intakes were 5·3, 10·4, 10·6 and 6·7 (SE 0·74) MJ/d and apparent digestible CP intakes were 37, 50, 79 and 68 (SE 4·3) g/d for Control, M, H and P treatments respectively. Splanchnic tissue oxygen consumption rates were 0·23, 0·32, 0·30 and 0·27 (SE 0·054) mol/h, and oxidative metabolism accounted for 0·46, 0·31, 0·33 and 0·47 (SE 0·051) of DE intakes for Control, M, H and P treatments respectively. Supplements increased (P 0·05) release of α-amino nitrogen (AAN) by the PDV (4·2, 17·5, 19·6 and 18·1 mmol/h for Control, M, H and P treatments respectively). Splanchnic net flux of AAN was not affected by supplement treatments. Hepatic release of urea-N was increased (P 0·05) by supplement treatments (27, 40, 46 and 44 mmol/h for Control, M, H and P respectively); the P treatment increased (P 0·05) and the H treatment tended (P = 0·10) to increase splanchnic release of urea-N (7, 10, 20 and 27 mmol/h for Control, M, H and P treatments respectively). Net flux of glucose across the PDV was -4·6, 1·4, -5·6 and -7·2 (SE 1·65) mmol/h for Control, M, H and P treatments respectively. Hepatic glucose released averaged 23 (SE 2·0) mmol/h and was not affected by treatment. Treatments M and H increased (P 0·05) PDV release of propionate compared with the Control treatment (4·5, 15·5, 16·8 and 7·7 mmol/h for Control, M, H and P treatments respectively). Release of acetate by the PDV was 43, 97, 118 and 67 (SE 23·9) mmol/h for Control, M, H and P treatments respectively. In summary, different supplements of low-quality grass did not increase the efficiency of N metabolism by splanchnic tissues. Treatment P had little effect on net flux across splanchnic tissues of glucose, L-lactate. β-hydroxybutyrate and volatile fatty acids (VFA). Overall, treatments M and H had similar effects on splanchnic net fluxes of VFA and L-lactate whereas butyrate and β-hydroxybutyrate releases by the PDV were increased by treatment M.

In order to determine how soya-bean proteins are digested and metabolized in the human intestine before colonic bacterial fermentation and to estimate their true digestibility, the gastro-jejunal behaviour of soya-bean proteins in water and in two other forms (a concentrated soya-bean-protein solution (isolate) and a drink composed of crude soya-bean proteins (soymilk)) was studied in humans. Experiments were carried out in eight healthy volunteers using a double-lumen steady-state intestinal perfusion method with polyethyleneglycol (PEG) as a non-absorbable volume marker. Gastric emptying and N and electrolyte contents of the jejunal digesta were analysed. Gastric half-emptying time (min) of the liquid phase after water ingestion (12·59 (SE 0·12)) was shorter (P < 0.05) than those for soymilk (37·74 (SE 11·57)) and isolate (36·52 (SE 11·23)). Electrolytic balances showed that for all meals, Na+, Cl− and K+ were secreted when Ca2+ was efficiently absorbed from the jejunal lumen. Gastro-jejunal N absorption for isolate and soymilk were 63 and 49% respectively, and were not significantly different from one another; after water ingestion, endogenous N was estimated to be 21 mmol. An estimate of the exogenous: endogenous values for the effluents was obtained from the amino acid compositions of soymilk and effluents after water or soymilk ingestion, indicating that 70% of the total N was exogenous and 30% endogenous. Under these conditions the endogenous fraction represented 31 mmol after soymilk ingestion and the gastro-jejunal N balance indicated that 54% of the soymilk was absorbed. This finding indicates that the true gastro-jejunal digestibility of soya-bean proteins is similar to that of milk proteins.

Three experiments were conducted to examine the effect of heating field peas (Pisum sativum cultivar Dundale) on (1) proximate analysis and total amino acid composition, (2) ileal and faecal digestibilities of amino acids, and (3) digestible energy content. Alternative techniques for assessing ileal and faecal digestibilities and digestible energy respectively, were also investigated. Forced-air dehydrators were used to heat field peas at temperatures of 110°, 135°, 150° or 165°. In the first experiment the apparent ileal and faecal digestibilities of amino acids and the faecal digestibility of energy in the raw and heated field peas were determined using pigs fitted with ‘T’ -shaped cannulas. In the second, apparent ileal digestibility of amino acids and the faecal digestibility of energy were determined using the direct ileal and rectal sampling technique. This involved a single collection of digesta and faeces from the digestive tract of the pig while it was anaesthetized. The faecal digestibilities of amino acids and energy were determined using total faeces collection in the third experiment. In all experiments the respective field-pea treatments comprised 400 g/kg sugar-based diets and were the only source of amino acids. Heat significantly decreased the lysine (14.6–8.7 g/kg; P < 0.001), cystine (3.2–2.6 g/kg; P < 0.01) and arginine (16.7–14.5 g/kg; P < 0.05) contents of the heated peas. The ‘reactive’ lysine content of the field peas, as measured using the Silcock technique, was decreased by 0.11 and 0.30 with the application of heat at 150° and 165° respectively. Heat treatments did not alter the ileal digestibility of most amino acids. Only aspartic acid (0.72–0.58), glutamic acid (0.80–0.65) and the basic amino acids, lysine (0.79–0.56) and arginine (0.85–0.75), showed a significant linear decrease (P < 0.05) in ileal digestibility over the heat treatments, determined using the ileal cannulation procedure. Heating significantly (P < 0.05) decreased faecal digestibility for all amino acids. Faecal digestibility was consistently greater than ileal digestibility for the raw field peas; however, this difference decreased with heat application until faecal digestibility was equal or less than ileal digestibility at the 165° treatment. Heat linearly depressed digestible energy, diet dry-matter digestibility and diet energy digestibility. Losses in lysine, cystine and arginine are likely to be due to early and advanced Maillard reactions. Considerable binding of the remaining lysine also occurred as indicated by a decline in Silcock-reactive lysine. The results indicate that the direct ileal sampling technique is a viable alternative to the cannulation procedure for amino acids, but further method development is required to decrease the variability associated with measurements. The estimation of faecal digestibility using indigestible markers and the partial faeces collection technique was as efficient as total faeces collection. In general, ileal digestibility of amino acids showed little response to heating, however, any changes that were observed were greatest for lysine. In contrast, faecal digestibility of all amino acids was greatly reduced with increasing heat application. This response appeared to be largely due to the effect of heating on microbial degradation and synthesis of amino acids in the hind-gut, rather than a reflection of the changes within the protein induced by heating. This variable response makes faecal digestibility an unreliable estimator of amino acid ileal digestibility.

Apparent digestible efficiency (% DE) was studied by use of dietary Mn as an inert marker, in minke whales (Balaenoptera acutorostrata) and crabeater seals (Lobodon carcinophagus) which had been eating krill. Median % DE in minke whales (n 5) eating krill of the genus Thysanoessa sp. (energy density (ED) 23·8 kJ/g) was 93 (range 87–93). Median % DE in crabeater seals (n 6) eating krill of the species Euphausia superba (ED 20·8 kJ/g) was 84 (range 79–85), which is significantly lower than the % DE of krill in minke whales (P = 0·008). Since the chemical composition in E. superba and in Thysanoessa sp. is similar, it is suggested that the complex multi-stomached system of minke whales, which contains both chitinase (EC 3.2.1.14)-producing as well as several other types of bacteria, is superior to the single-stomached system of crabeater seals with regard to krill digestion. It is worth noting, however, that the % DE of krill in the crabeater seal is still very high.

The time-course effects of two diets containing raw (RSF) or heated (HSF) soya-bean flour on the digestive enzyme levels in the pancreas and in pancreatic juice were investigated in growing rats fed, alternately, on RSF or HSF diets for two 4-week periods. These values were compared with those obtained in a control group fed on a casein diet. RSF and HSF diets lowered N balance (84.8 (SE 0.9), 82.6 (SE 0.8) and 79.9 (SE 0.8) % with control, HSF and RSF diets respectively, at the third week). However, they increased protease activities compared with the control diet (3-fold for trypsin (EC 3.4.21.4) and chymotrypsin (EC 3.4.21.1) activities in pancreas contents and outputs with the RSF diet; 2-fold for trypsin in pancreas contents and outputs and by 60% for chymotrypsin contents with the HSF diet). The poorer nutritional N utilization might be attributable to soya-bean flour heat-stable (lectins) and heat-labile components (trypsin inhibitors). The decrease in lipid apparent digestibilities in RSF and HSF diets (97.0 (SE 0.8), 91.1 (SE 09) and 90.4 (SE 0.7) % with control, RSF and HSF diets at the seventh week) were correlated with a diminution in apparent lipase (EC 3,1.1.3; measured without addition of exogenous colipase), potential lipase (measured with addition of saturated amounts of exogenous colipase) and colipase activities. Compared with control values, gains in potential and apparent lipase outputs were diminished by nearly 40% and gain in colipase outputs by 60% with RSF and HSF diets. These results show clearly that heated or raw soya-bean flours have a significant inhibitory effect on lipase digestive enzyme activities in the pancreas and in its secretion, which might explain impaired lipid digestibility.

There is a paucity of data on differences between methods for the assessment of body composition in elderly subjects. Studies on younger adults suggest that such differences are of some practical significance at the individual level. In the present study the following methods of estimating percentage body fatness (BF%) were compared in healthy elderly men and women (mean age 70 (SD 6) years: densitometry; skinfold thickness; total body water; bioelectrical impedance (BIA) using an age-specific predictive equation and the manufacturers' equation; body mass index (BMI). Though BF% estimates from the various methods tended to be highly correlated with those from densitometry and with each other, differences between methods at the individual level were marked. In particular, the age-specific equations based on BMI and BIA systematically overestimated BF% relative to the other methods. Biases between BF% estimates derived from densitometry, skinfolds, BIA (manufacturers' equation) and total body water were less marked, indicating little evidence of systematic differences between these methods in elderly subjects. Individual differences between methods were slightly greater than those reported in some studies of younger adults, but this may be of little practical significance, and may be considered inevitable in view of variability between and within subjects in the extent to which the underlying assumptions of these two-component methods are met in elderly subjects.

To determine whether the amino acid composition of milk changes during lactation, we compared the amino acid pattern (concentration of each individual amino acid relative to the total amino acid concentration) of colostrum with that of mature milk in six mammalian species. In the human, horse, pig and cow, the pattern of amino acids changed between colostrum and mature milk: glutamate, proline, methionine, isoleucine and lysine increased; cystine, glycine, serine, threonine and alanine decreased. In these four species, the total amino acid concentration also decreased 75% between colostrum and mature milk. In the baboon (Papio cynocephalus anubis and Papio cynocephalus anubis/Papio cynocephalus cynocephalus) and rhesus monkey (Macaca mulatta), however, there was little change in the pattern of amino acids between colostrum and mature milk, and total amino acid concentration decreased only about 25% between colostrum and mature milk. Mature milk rather than colostrum was the most similar among the three primates in both amino acid pattern and total amino acid concentration. We conclude, in those species in which total amino acid concentrations decline substantially between colostrum and mature milk, amino acid patterns also change. The presence of a change in amino acid pattern and total amino acid concentration during lactation appears to be unrelated to phylogenetic order.

βCarotene-15,15′-dioxygenase (EC 1.13.11.21; β-carotene dioxygenase) activity in extracts from guinea-pig intestinal mucosa was assayed by supplying [15,15′-14C2l- or [15,15′-3H2]β-carotene dissolved in Tween 80. Methods were developed to minimize the breakdown of labelled β-carotene and β-carotene cleavage products during the isolation procedure. Antioxidants and unlabelled carriers were added to extracting solvents and C18 Sep-Pak cartridges were used to isolate the remaining β-carotene and retinaldehyde, which was the only cleavage product detected. The labelled material produced by the enzyme was analysed by either normal-phase TLC or reversed-phase HPLC and characterized chemically as retinaldehyde. The lack of other labelled up-carotenals isolated in these experiments and the formation of between 1.5 and 2 mol retinaldehyde/mol β-carotene consumed confirm the central cleavage mechanism for the enzyme's action. More β-carotene dioxygenase activity was obtained from guinea-pig mucosa than from chicken or pig intestinal mucosa. The β-carotene dioxygenase was obtained as a soluble enzyme which was partially purified by gel filtration and ion-exchange chromatography to a specific activity of 0.6 nmol retinaldehyde formedlmg protein per h. The formation of a lipid-protein aggregate containing the β-carotene dioxygenase activity, which has been reported to be present in the exclusion volume of Sephadex columns, was avoided if the mucosal serapings were homogenized in buffer at a proportion of 1:4 (w/v).

The interaction between essential dietary components and changes in tissue nutrient reserves, egg quality and egg composition, were studied from 60 d before and during the spawning of Sparus aurata broodstock. Fish were given isonitrogenous (550 g/kg dry weight) and isolipidic (100 g/kg dry weight) diets, based on protein and lipid extracts of squid meal. Diets differed in the levels of n−6 (10–30 mg/g dry weight) and n−3 (0–10 mg/g dry weight) essential fatty acids. The effects of these diets on biochemical and fatty acid composition of body tissues, and the subsequent effects on egg composition and egg viability were measured. Dietary essential fatty acids were mostly incorporated into the liver, ovaries, digestive tract and associated adipose tissues. The lipid composition of these tissues reached an equilibrium with dietary lipid composition within 15 d of feeding on any given diet. Muscle and gill cartilage tissues did not show any significant changes in their biochemical and fatty acid composition, even after 60 d feeding. Egg viability decreased significantly within 10 d of feeding the broodstock with a diet deficient in n−3 highly unsaturated fatty acids (n−3 HUFA). The levels of n−3 HUFA in both polar and neutral fractions of egg lipid were directly correlated with their levels in the broodstock diet. When the total amount of egg n−3 HUFA dropped below 17 mg/g dry weight, egg viability and larvae hatching rate decreased by 53% and 47 % respectively. These results suggest that the biochemical composition of organs involved in S. aurata reproduction are highly sensitive to the nutritional value of the diet, which affects egg and larval quality rapidly.

Several proteins with high proportions of S-containing essential amino acids were incubated in sheep rumen fluid in vitro and their rate of digestion was examined by sodium dodecyl sulphate-polyacrylamide-gel electrophoresis. The S-rich proteins rice prolamin (10 kDa), maize zein (10 kDa) and the 3·2 kDa pumpkin (Cucurbita maxima L.) trypsin inhibitor-1 (CMTI-1) were highly resistant to rumen fluid degradation, relative to control proteins of known degradation rate (casein, bovine serum albumin (BSA) and pea (Pisum sativum) albumin-1 (PA1)). Comparison of PA1 and a recombinant N-terminal epitope-tagged PA1 indicated that addition of the epitope caused a slight increase in resistance to rumen degradation. The proteins were also incubated with a mixture of trypsin (EC 3·4·21·4) and chymotrypsin (EC 3·4·21.1). PA1, BSA and casein were hydrolysed less rapidly than rice prolamin, maize zein and CMTI-1. Digestion by these intestinal proteases appeared to be complete. Thus, the prolamin, zein and CMTI-1 proteins are suitable candidates for expression as foreign proteins in pasture plants to increase throughput and uptake of essential amino acids in sheep.

Four pigs fitted with two sets of re-entrant cannulas in the upper jejunum were used to study the effect of two oat-flour (F)- and oat-bran (B)-based diets without or with (FC and BC respectively) addition of 148 g wood cellulose/kg on jejunal flow and absorption of glucose over an isolated loop of jejunum. Mean transit time (MTT) of flow from the proximal re-entrant cannula increased from approximately 1·5 h with diet F to 2 h when feeding diet BC. Both the replacement of oat flour by oat bran and the supplementation of the diets with cellulose led to a significantly longer MTT for dry matter and the carbohydrates, except that cellulose did not have a significant effect on the MTT for the total non-starch polysaccharides. Only the addition of cellulose significantly delayed gastric emptying of the added liquid-phase (Polyethylene glycol 4000) and solid-phase (Cr2O3) markers, whereas no effect of the oat source used was seen. Feeding diets with a higher level of dietary fibre (DF) and lower content of starch, obtained by substitution with cellulose or by feeding oat bran instead of oat flour, reduced the recovery of starch from an isolated loop of jejunum. Consequently, the quantitative absorption of starch was not significantly different between diets when starch was related to the recovery of external markers. However, when related to the recovery of arabinoxylan (AX) there was a significantly lower absorption of starch from the bran-based diets in comparison with the flour-based diets. The capacity to digest and absorb the large quantities of starch entering the duodenum after a carbohydrate-rich meal appears to be the limiting factor for absorption in the upper jejunum. Therefore, any effect of DF on the rate of absorption of glucose is presumably an effect on gastric emptying rather than displacement of the site of starch absorption in the small intestine.

In order to study the influence of pancreatic enzyme secretion on the intestinal absorption of mediumchain fatty acids (MCFA), three growing pigs (mean body-weight 61 kg) with ligated and severed pancreatic ducts were fitted with a permanent fistula in the duodenum and with two catheters in the portal vein and carotid artery respectively. An electromagnetic flow probe was also set up around the portal vein. A mixture of octanoic and decanoic acids, esterified as medium-chain triacylglycerols, together with maltose dextrine and a nitrogenous fraction was continuously infused for 1 h into the duodenum. Samples of blood were withdrawn from the two vessels at regular intervals of time for 8 h and further analysed for their non-esterified octanoic and decanoic acid contents. The concentrations of non-esterified octanoic and decanoic acid in the portal blood increased slowly after the beginning of each infusion, reaching about 10 times higher values than the basal level. Only 26% of octanoic acid infused in the duodenum and 27% of decanoic acid were recovered in the portal flow throughout each experiment. The possible mechanisms underlying the appearance of MCFA in the portal blood in the absence of pancreatic enzyme secretions and the importance of duodenal absorption of MCT in such physiological conditions have been discussed.