A factorial 3 × 3 experiment was conducted with chicks to investigate the effect of manipulating crude protein (N × 6.25) intake (CPI) and metabolizable energyintake (MEI) simultaneously, in the range low to high (including adequate) levels with regard to the respective requirements, on whole-body protein turnover and its contribution to total heat production. The fractional rate of whole-body protein synthesis was increased curvilinearly by increasing MEI or CPI from low to high levels. In terms of absolute rates whole-body protein synthesis was enhanced by increasing MEI from low to adequate levels, the effect being greater at adequate and high CPI than at low CPI. The effect of varying CPI and MEI on whole-body protein degradation was similar, but less sensitive, to that on whole-body protein synthesis. Increasing MEI from low to high levels elevated totalheat production at all CPI levels. There were no interactive effects of varying CPI andMEI on the contribution of whole-body protein synthesis to total heat production, and in general the contribution increased with increasing CPI and decreased with increasing MEI.The contribution of whole-body protein synthesis to total heat production fell within a small range from 11.2 to 16.5%.

The effect of rumen liquid volume, pH and concentration of volatile fatty acids (VFA) on the rates of absorption of acetic, propionic and butyric acids from the rumen was examined in lactating dairy cows. Experimental solutions introduced into the emptied, washed rumen comprised two different volumes (10 or 30 1), four levels of pH (4.5, 5.4, 6.3, 7.2) and three levels of individual VFA concentrations (20, 50 or 100 mM-acetic, propionic or butyric acid). All solutions contained a total of 170 mM-VFA and an osmotic value of 400 mOsmol/l. Absorption rates were calculated from the disappearance of VFA from the rumen corrected for passage with liquid phase to the omasum. An increase in initial fluid pH caused a reduction in fractional absorption rates of propionic and butyric acids. Increasing the initial pH from 4.5 to 7.2 reduced fractional absorption rates of acetic, propionic and butyric acids from 0.35, 0.67 and 0.85 to 0.21, 0.35 and 0.28/h respectively. The fractional absorption rates of all VFA were reduced (P < 0.05) by an increase in initial rumen volume. The fractional absorption rate of acetic acid was lower (P < 0.05) at an initial concentration of 20 mM than of 50 mM. The fractional absorption rate of propionic acid tended (P < 0.10) to decrease as the level of concentration increased while fractional absorption rate of butyric acid was not affected by butyric acid concentration. These results indicate that relative concentrations of VFA in rumen fluid might not represent relative production rates and that attempts to estimate individual VFA production from substrate digestion must take account of pH and VFA concentration.

The aim of the present study was to investigate the effect of soya-bean protein on growth and muscle metabolism in fish. Cod, Gadus morhua, were fed on a fish-feed formula with the high-quality fish-meal protein being replaced by 100, 200 or 300 g soya-bean protein/kg fish-meal protein. The feeding experiment lasted for 43 d at a water temperature of 7–8º and a sea water salinity of 3.5%. At the 200 g/kg level of soya-bean protein, food intake and growth rate were similar to those of the controls. At the 300 g/kg level of soya-bean protein, food intake was diminished by 6 % and growth by 67 % relative to control levels. In muscle, sarcoplasmic protein (/g wet weight) was significantly decreased by 14%. Myofibrillar protein (/g wet weight) was unchanged. Levels of RNA in the myofibrillar fraction decreased at all three levels of soya-bean protein, and that of the sarcoplasmic fraction decreased at the highest level of legume-protein. With increased levels of soya-bean protein, RNA: DNA declined by 18% from 1.88 to 1.54. The contractile protein myosin heavy chain (/mg protein and /g wet weight) and myosin heavy chain-specific mRNA (/mg RNA) were not significantly affected by dietary conditions. Expressed per g wet weight, the decline by 21 % of the specific mRNA depended on the total RNA content which decreased with the increase in soya-bean protein. Acid proteinase activity was lowest at the 200 g/kg level, showing a decrease of 23%. Glycogen content fell by 46% at both the 200 and 300 g/kg level of dietary soya-bean protein. The results show that muscle metabolic functions responded to the dietary plant protein before there were any measurable changes in growth rate. From the results it is concluded that 200 g/kg or less of the high-quality fish-meal protein may be replaced by soya-bean protein in a fish-feed formula.

Lack of sufficient methionine and lysine delivered post-ruminally may limit milk production response to bovine somatotropin (bST). To test this hypothesis, four Holstein cows fitted with rumen and duodenal cannulas were used in a 4 × 4 Latin square design with 14 d periods. Treatments were: (1) control, (2) continuous duodenal infusion of 8 g methionine and 24 g lysine/d, (3) injection of 25 mg bST/d and (4) infusion of methionine and lysine plus injection of bST. Infusion of amino acids led to trends for small increases in milk (3%), fat (5.5%), and protein (3.7%) yield. Larger and significant increases (8.7, 14 and 6.9% for milk, fat and protein yield respectively) were achieved with bST administration which also increased milk fat content. Plasma levels of urea-N and essential amino acids were reduced with bST. Duodenal nutrient flow was generally unaffected by treatment. The production response to bST was not enhanced in cows producing an average of 34 kg milk when provided additional methionine and lysine post-ruminally in this short-term study.

The effect on lactational performance of replacing feed carbohydrate with fat at two different protein levels was studied. Lactating Sprague–Dawley rats with a standardized litter size of thirteen pups were allocated one of eight feeds containing either 300 or 150 g protein/kg organic matter (OM) and ranging in fat content from 100 to 550 g/kg OM from day 2 until day 14 of lactation. Daily food intake, live-weight gains, and changes in body composition of both dams and litters were measured. Feeds of low protein content resulted in a significant decline (P < 0.001) in lactational performance despite a significant increase (P < 0.001) in maternal protein mobilization. Maternal lipid mobilization was not significantly affected by feed composition. Litter lipid gain was significantly increased (P < 0.05) as fat replaced carbohydrate in the high-protein feeds, due to an increase in maternal energy intake. In contrast, lactational performance was severely depressed (P < 0.001) as fat replaced carbohydrate in the low-protein feeds. This interaction between feed components on lactational performance was in accordance with the hypothesis that the heat production of lactating rats is maximal and, hence, constraining intake.

Rumen-cannulated Holstein cows were used to study the effect of intraruminal dosing of dioctyl sodium sulphosuccinate (DSS; 0.07 g/kg body weight per d) for 4 weeks. DSS was suspended in nylon bags to allow it to be released slowly into the rumen. Cows were offered a diet containing grass silage and concentrate (45:55, w/w). Intakes of control cows were regulated to those of DSS-dosed cows. Cows dosed with DSS had no rumen ciliate protozoa, lower rumen NH3-N concentrations and acetate and butyrate proportions, higher propionate, isovalerate, and valerate proportions. In vitro fibre digestion by non-ciliate rumen fluid from DSS-dosed cows was apparently impaired. When cows were dosed with DSS, levels of neutral- and acid-detergent fibre in whole rumen contents were increased, rumen solids turnover rate was slower, and whole tract apparent digestibility of cellulose and diethyl ether extract was decreased. Dosing of DSS led to reduced concentrations of blood acetoacetate but elevated plasma glucose levels. Milk protein content was higher, however, lactose content was lower for DSS-dosed than control cows. Milk fat of DSS-dosed cows had a smaller proportion of short-chain fatty acids but a greater proportion of unsaturated fatty acids.

Rumen-fistulated lactating cows were individually fed on hay or silage and intakes were monitored during 3 h treatment periods and for 2 h after. Each experiment used five, six or seven animals and the treatments were applied in a Latin Square design. Sodium acetate infusions of 1·8–11·0 mol in 4.5 litres water caused a dose-related depression in hay intake, the extent being 82 g dry matter (DM)/mol infused (P < 0·01). Sodium acetate infusions of 6·0–15·0 mol in 4·5 litres water caused a dose-related depression in silage intake of 118 g DM/mol infused. Rumen fluid pH for both diets was unaffected by treatment. Acetate and Na concentrations were increased and significantly negatively correlated with intake of both diets. Infusions of 2–8 mol sodium propionate caused a dose-related depression of hay intake which was significant when cow and day effects were accounted for. Sodium propionate infusions of 4–8 mol significantly depressed silage intake by 140 g DM/mol infused (P < 0·001). Rumen fluid pH was unaffected by treatment while propionate and Na concentrations were elevated and significantly negatively correlated with intake for both diets. Inflation of a rubber balloon in the rumen with 12.5–20 litres warm water resulted in a dose-dependent depression in hay intake of 66 g DM/1 distension (P < 0·05). There was significant overeating during the 2 h following the 20 litre treatment. With silage, 15–25 litres of balloon distension for 3 h resulted in a dose-dependent depression in intake of 28 g DM/l distension (P < 0·001). There was no significant overeating during the 2 h following distension. When given in physiological amounts, at the lower end of the range used in these experiments, acetate, propionate and distension of the rumen did not significantly affect hay intakes. However, in each case the linear relationship between intake depression and level of treatment suggested that these factors could contribute to the control of feed intake.

In order to test the hypothesis that negative leedback signals from abdominal receptors are integrated in an additive manner in the control of voluntary food intake, cows with rumen fistulas were given intraruminal infusions of sodium acetate or sodium propionate, cr both, with or without distension of the rumen by balloon. Intakes were monitored during the 3 h experimental period and for 2 h after and samples of rumen fluid were taken for estimation of short-chain fatty acid concentrations and osmolality. Six cows in mid-lactation were fed on hay and concentrates and given, into the rumen. 5.5 mol sodium acetate, 5.2 mol sodium propionate and 7.51 of distension. Compared with the control (water infusion), neither acetate, propionate nor distension significantly depressed hay intake when given separately. When given in combination, however, the following significantly depressed intake during the 3 h treatment period: propionate + distension, acetate + distension, acetate + propionate + distension. Seven cows in early lactation were fed on silage and concentrates and given, into the rumen, 9.0 mol sodium acetate, 4.0 mol sodium propionate and 10.0 litres of distension. Again, none of the three given alone depressed silage intake to a significant extent during the 3 h treatment period, whereas the following combinations had a significant effect: propionate + distension, acetate + distension, acetate + propionate + distension. Basal rumen osmolalities were similar for the two types of feed but infusion of the sodium salts caused a very much greater increase with silage than with hay. The results are discussed with regard to the implications for our understanding of the control of voluntary intake and the likely role of chemo-, osmo- and mechano-receptors.

The effect of four species of legume seeds on plasma cholesterol levels and faecal steroid excretion was studied in pigs. Thirty-six growing boars were randomly allocated in groups of six to six diets which they ate continuously for 42 d. The diets fed were: 1, a semi-purified (SP; control group 1) diet; 2, SP 10 g cholesterol/kg (control group 2); 3, 4, 5, 6, SP + cooked legumes (70:30, w/w; respectively baked beans (Phaseolus vulgaris), peas (Pisum sativum), lentils (Lens culinaris Medik.), butter beans (Phaseolus lunatus)) + 10 g cholesterol/kg. Fasting blood samples were taken on days 0, 14, 28, and 42 for the determination of total plasma cholesterol, high-density-lipoprotein (HDL)-cholesterol and triacylglycerols. Between days 7 and 11 and days 28 and 32 complete 5 d faecal collections were made for the measurement of neutral, acidic and conjugated steroids. After 42 d total cholesterol and HDL-cholesterol levels were raised significantly in all groups, but to different extents. In comparison with control group 2, diet-induced hypercholesterolaemia was significantly inhibited in the groups consuming baked beans, peas and butter beans, although HDL-cholesterol levels were maintained. Faecal steroid excretion by the legume groups was not significantly different from that of control group 2. The results suggest that the mechanism for the hypocholesterolaemic effect does not involve increased hepatic bile acid synthesis and thereby increased cholesterol clearance via the intestinal route.

Effect of quantity and nutritional quality of dietary proteins on the content of mRNA of insulin-like growth factor-binding protein-1 (IGFBP-1) was studied in rat liver and kidney. IGFBP-1 mRNA content per unit RNA increased in liver and kidney of rats fed on a protein-free diet and in those of fasted rats compared with that in the rats fed on a casein diet. When rats were given a gluten diet for 7 d, IGFBP-1 mRNA content in liver did not change significantly but that in kidney increased considerably compared with that in those organs of the rats fed on the casein diet. Because IGFBP-1 mRNA has been demonstrated both in liver parenchymal and non-parenchymal cells (Takenaka et al. 1991), the effect of the protein-free diet on these two types of cells has been studied. An increase in IGFBP-1 mRNA content under protein deprivation was observed in both liver parenchymal and non-parenchymal cells, suggesting that these two types of cells are regulated in a similar mode as far as IGFBP-1 mRNA content is concerned. The physiological and nutritional significance of the previously stated results on protein anabolism are discussed when considered together with our previous observations on the plasma concentrations of IGF-1 (Takahashi et al. 1990) and IGFBP (Umezawa et al. 1991) and insulin-like growth factor-1 mRNA content in liver (Miura et al. 1991).

The relationship between digestive enzyme activities in the pancreas and pancreatic juice was studied in post-weaning rats fed on a low-protein diet (30 g cereal protein/kg) for 1 month and a refeeding balanced diet (235 g mixed protein/kg) for the following 3 months. A control group was fed on the balanced diet for 4 months. At the end of malnutrition and at various times of refeeding, activities of amylase (EC 3.2.1.1), trypsin(EC 3.4.21.4), chymotrypsin (EC 3.4.21.1), lipase (EC 3.1.1.3), phospholipase A2 (EC 3.1.1.4) and cholesterolesterase (EC 3.1.1.13) in pancreas and pancreatic juice were measured. Recovery of body and pancreas weights was obtained after 3 months of refeeding. Pancreas offered a higher resistance to the low-protein diet; a quicker recovery than that of the whole organism was observed during refeeding. Protein and RNA contents of pancreatic cells were depressed by protein depletion. At the end of refeeding, pancreatic and cell RNA contents were still depressed. In pancreas and pancreatic juice, protein depletion produced a decrease in enzyme activities, with the exception of phospholipase A2 and cholesterolesterase. During refeeding, activities were increased to various levels in pancreatic juice and pancreas. In pancreatic juice, a deficit in enzyme activities still prevailed at the end of refeeding. The retention thresholds (total activity in pancreas v. activity per h in pancreatic juice) of hydrolases were increased by malnutrition. They were all decreased by refeeding at various rates, but after 3 months of refeeding the thresholds were still markedly increased for all enzymes studied. After malnutrition and during refeeding, the dissociated enzyme activities in pancreas and pancreatic juice could be the expression of an alteration at different stages: synthesis, intracellular transport, storage mechanisms and secretion.

The influence of increasing intakes of fish oil on spleen leucocyte phospholipid fatty acid composition and cell-mediated immunity was studied in the mouse using a popliteal lymph node assay technique. The immune response was suppressed by 160 g fish oil/kg diet, but not by lower doses. The proportion of 20: 5n-3 in spleen leucocyte phospholipid increased from 0.14 in the controls to 3.8, 7.2, 8.5 and 9.4% in the animals fed on 25, 50, 100 and 160 g fish oil/kg diet; the proportion of 22: 6n-3 increased from 5.1 in the controls to 12.1, 12.2, 12.8 and 12.9% respectively. It is concluded that moderate intakes of fish oil are not immunosuppressive.

The present study examined the effect of urea-N supplementation of a N-deficient diet on digestion and metabolism in the rumen. Five Rasa Aragonesa ewes, each fitted with a rumen cannula, were offered alkali-treated barley straw ad lib. alone or supplemented continuously via the cannula with four levels of urea-N (3, 6, 9 and 12 g/d). Rumen NH3 concentrations increased in response to urea infusion (6–128 mg/l; P < 0.001). At the highest level of rumen NH3 concentration there was a significant increase, compared with the unsupplemented treatment, in dry matter (DM) intake (846–1206 g/d; P < 0.001) and apparent digestibility of DM (0.38–0.43), organic matter (0.38–0.45) and neutral-detergent fibre (0.41–0.49; P < 0.01). Rumen outflow rates of particulate matter and potential DM disappearances, assessed using nylon bags, were not affected by the experimental treatments, although fractional rate of DM disappearance increased significantly with increasing levels of urea infusion (2.4–4.6 per h). Urinary excretion of total purine derivatives increased with N supplementation, although the response was exclusively due to an increase in allantoin excretion (26.9–66.4 mg/kg live weight (W)0.75 per d; P < 0.001). Xanthine, hypoxanthine and uric acid excretion rates were constant, averaging 1.8 (SE 0.17); 5.4 (SE 0.21) and 7.2 (SE 0.36) mg/kg W0.75 per d respectively. The maintenance of a minimum rumen NH3 concentration (approximately 50 mg/l) was necessary to avoid significant reductions in DM intake and fermentation rate. Higher levels, however, may further increase microbial N flow at the duodenum, as suggested by the response in urinary allantoin excretion over the range of rumen NH3 concentrations.

The effect of dietary protein and fat levels on cardiac mitochondrial oxidative phosphorylation was assessed polarographically. Weanling rats were fed on semi-purified diets containing different protein levels (10, 30, 50 and 70%) on a gross energy basis (PGE) for 9, 23 and 58 d. Cardiac mitochondria isolated from rats fed on a 70% PGE diet for 23 d exhibited significantly reduced ADP: oxygen (ADP: O) values compared with mitochondria from rats fed on a low-protein diet. Feeding low-protein diets for 58 d increased the ADP:O value. When the dietary fat level was altered to provide (% PGE: % fat-energy): 30:14, 30:30, 70:14, 70:30, feeding 70% PGE diets reduced the ADP:O value compared with the 30 % PGE level, but no difference was observed between low-fat and high-fat groups. These results indicate that the impaired ADP:O value for rats fed on very-high-protein diets was not due to the dietary fat level but that the level of dietary protein is an important determinant of oxidative phosphorylation in rat heart mitochondria.

In order to study the rate of intestinal absorption and hepatic uptake of medium-chain fatty acids (MCFA), six growing pigs, mean body weight 65 kg, were fitted with a permanent fistula in the duodenum and with three catheters in the portal vein, carotid artery and hepatic vein respectively. Two electromagnetic flow probes were also set up, one around the portal vein and one around the hepatic artery. 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 three vessels at regular intervals for 12 h and further analysed for their non-esterified octanoic and decanoic acid contents. The concentration of non-esterified octanoic and decanoic acids in the portal blood rose sharply after the beginning of each infusion and showed a biphasic time-course with two maximum values, one after 15 min and a later one between 75 and 90 min. Only 65 % of octanoic acid infused into the duodenum and 54 % of decanoic acid were recovered in the portal flow throughout each experiment. The amounts of non-esterified MCFA taken up per h by the liver were close to those absorbed from the gut via the portal vein within the same periods of time, showing that the liver is the main site of utilization of MCFA in pigs. These results have been discussed with a special emphasis laid on the possible mechanisms of the biphasic time-course of MCFA absorption and the incomplete recovery in the portal blood of the infused fatty acids.

The fate of a small oral dose of protein given to overnight-starved rats was studied. After 3 h, 62 % of the protein amino acids had been absorbed. Most of the absorbed N went into the bloodstream through the portal in the form of amino acids, but urea and ammonia were also present. About one-quarter of all absorbed N was carried as lymph amino acids. The liver was able to take all portal free ammonia and a large proportion of portal amino acids, releasing urea. The hepatic N balance was negative, indicating active proteolysis and net loss of liver protein.

Although high α-linolenic acid flaxseed (Linum usitatissitmum) is one of the richest dietary sources of α- linolenic acid and is also a good source of soluble fibre mucilage, it is relatively unstudied in human nutrition. Healthy female volunteers consumed 50 g ground, raw flaxseed/d for 4 weeks which provided 12–13% of energy intake (24–25 g/100 g total fat). Flaxseed raised α-linolenic acid and long-chain n-3 fatty acids in both plasma and erythrocyte lipids, as well as raising urinary thiocyanate excretion 2.2- fold. Flaxseed also lowered serum total cholesterol by 9 % and low-density-lipoprotein-cholesterol by 18%. Changes in plasma α-linolenic acid were equivalent when 12 g α-linolenic acid/d was provided as raw flaxseed flour (50 g/d) or flaxseed oil (20 g/d) suggesting high bioavailability of α-linolenic acid from ground flaxseed. Test meals containing 50 g carbohydrate from flaxseed or 25 g flaxseed mucilage each significantly decreased postprandial blood glucose responses by 27%. Malondialdehyde levels in muffins containing 15 g flaxseed oil or flour/kg were similar to those in wheat-flour muffins. Cyanogenic glycosides (linamarin, linustatin, neolinustatin) were highest in extracted flaxseed mucilage but were not detected in baked muffins containing 150 g flaxseed/kg. We conclude that up to 50 g high-α-linolenic acid flaxseed/d is palatable, safe and may be nutritionally beneficial in humans by raising n-3 fatty acids in plasma and erythrocytes and by decreasing postprandial glucose responses.

The kinetics of 3-methylhistidine (3MH) metabolism in four crossbred lambs were studied. Each lamb was injected with an intravenous dose of 3-[2H3]methylhistidine (d3-3MH) and the stable isotope disappearance in plasma and appearance in both urine and muscle were measured. Immediately after the administration of tracer there was a phase of rapid disappearance of tracer from the plasma, which was followed by a more gradual decrease in d3-3MH from the plasma during the last 4 d of the experiment. A minimum of three exponentials was required to describe the plasma decay curve adequately. The kinetic model of 3MH in the whole animal was constructed by using the SAAM/CONSAM computer modelling program. Two different configurations of a three-compartment model are described: (1) a simple three-pool model, in which plasma kinetics were entered into pool 1 out of which they had one undefinable exit; (2) a plasma-urinary three-pool model with two exits, in which the urinary kinetics were entered as an exit out of pool 1 and required a second exit out of pool 3 to produce an adequate fit. In addition, muscle kinetics from biopsies of the longissirnus dorsi were entered into either pool 2 or 3 using the plasma-urinary model. Steady-state mass and transport rate values were obtained for each model construct described, and a de novo production rate corresponding to a fractional breakdown rate of myofibrillar protein of approximately 5%/d was also calculated. The model predicted that only 15% of 3MH was excreted in urine as free 3MH, which is consistent with current knowledge of 3MH excretion in sheep. The simple three-pool plasma kinetic model, therefore, could be used to estimate, by a relatively simple injection-sampling technique, the extent of muscle protein turnover in lambs.

The effects of abomasal infusion of casein or soya-bean-protein isolate (SPI) on milk production were investigated in four Friesian cows in mid-lactation receiving a basal diet of grass silage and barley which supplied energy and protein considerably in excess of requirements for milk production by conventional rationing standards. Three levels of infusion were used for each protein source, the corresponding doses being isonitrogenous for each of the proteins: 100, 220 and 330 g/d for casein and 115, 230 and 345 g/d for SPI. Casein produced much greater effects on the yield of milk and milk constituents than did SPI. On the highest dose of casein, milk yield was increased by 3.5 kg/d, fat output by 15% and protein output by 36%; corresponding values for the highest dose of SPI were 1.6 kg/d, 12% and 13% respectively. Increases in the yield of milk-protein were linear for casein but for SPI there was no increase beyond the first level of infusion. It was calculated that casein infusion had a marked effect on the utilization of energy: the increases in milk production could be explained either by a channelling of an extra 12 MJ metabolizable energy (ME)/d away from body tissue synthesis and into milk synthesis or by an increase in the efficiency of utilization of ME for lactation from 0.50 on the basal diet to 0.58; the measurements made did not allow the two mechanisms to be clearly differentiated.

In attempting to evaluate alterations in metabolic responses to dietary nutrients that occur in pathological conditions in man, it is first necessary to understand normal metabolic responses. The present study set out to determine the temporal responses of protein synthesis in the skeletal muscle of healthy subjects to the consumption of food. Sequential measurements of protein synthesis in quadriceps muscle were made in eight subjects by injection of 0.05 g L-[l-13C]leucine/kg body-weight. The rate of protein synthesis after an overnight fast (i.e. in the post-absorptive state) was 2.2% muscle protein. After 1 h of eating, protein synthesis was unaltered (2.2%/d), but after 10 h of consuming small hourly meals the rate had risen to 2.9%/d, with a variation in response among individuals. The response of muscle to 10 h of feeding was also investigated in subjects who underwent only one measurement each, either after 10 h of eating small meals or after the same time-period when no food was given. Protein synthesis rates were only slightly elevated in the group of fed individuals (2.3%/d, n 6) compared with the fasted group (2.1%/d, n 6). Taken together the two studies suggest that in healthy adults muscle protein synthesis does not respond quickly to the influx of dietary nutrients and that even after 10 h of feeding any stimulation of protein synthesis is small.