Three series of nitrogen-balance experiments were carried out on growing rats fed on purified isonitrogenous diets (16 g N/kg) to study the importance of non-essential N and the essential:total N (E:T) ratio for attaining maximum N balance (NB) and biological value (BV) of protein. Minimum dietary levels of asparagine, proline and glutamic acid required for maximum NB and BV were estimated to be 1.0, 2.0 and 5.0 g/kg respectively. In an essential amino acid-based diet, the levels of individual amino acids were successively reduced to 110% of the requirement. Reducing the level of arginine, lysine or methionine + cystine resulted in a significant increase in NB and BV while the response of rats given the isoleucine-reduced diet significantly decreased. Addition of asparagine, proline and glutamic acid in the estimated minimum amounts to an essential amino acid-based diet resulted in a significant increase in NB and BV. A further significant increase was found when the levels of arginine, lysine and methionine + cystine in the diet were reduced to 110 % of the requirement. The performance of rats fed on the latter diet was similar to that of rats given a diet with the optimum E:T ratio. It is concluded that the optimum protein utilization may be influenced by the presence of some non-essential amino acids and by the surplus of some essential amino acids rather than by the E:T ratio per se.

Wether sheep were fitted with rumen fistulas and polyethylene tubes to the abomasum and were given all nutrients by intragastric infusion. In Expt 1 volatile fatty acids (VFA) were given at 340, 450 and 630 kJ gross energy (GE)/kg metabolic weight (W0.75) and protein at 0, 150, 300, 600, 900 and 1500 mg nitrogen/kg W0.75. In Expt 2 VFA were infused at 450 kJ GE/kg W0.75 and protein at 0 and 300 mg N/kg W0.75. At all levels of energy intake in Expt 1 the N retention was significantly (P < 0.01) related to N intake. The basal N requirement was estimated to be 281 mg (SE 21.8) N/kg W0.75 at 340 kJ VFA/kg W0.75, 226 (SE 21.8) mg N/kg W0.75 at 450 kJ VFA/kg W0.75 and 207 (SE 19.4) mg N/kg W0.75 at 630 kJ VFA/kg W0.75. Plasma urea concentrations varied markedly in relation to protein intake and to energy supply. On the other hand plasma ammonia, glucose, insulin and creatinine concentrations, and also urinary excretion of purine derivatives and creatinine were not significantly affected by the treatments imposed. It was concluded that the urinary excretion of purine derivatives in ruminants was largely unaffected by moderate changes in energy intake and by large changes in protein intake.

The aim of the present experiment was to determine the influence of either probiotic or antibiotic inclusion in the diets of pigs from birth on the development of enzyme activity in the small intestine. Pigs were fed on creep feed and grower diets containing either a probiotic, an antibiotic or no added growth promoter. At 7, 17, 42 and 80 d of age pigs from each treatment group were sampled to investigate the development of carbohydrase and peptidase activity in the mucosa at five sites along the small intestine. Inclusion of either the probiotic or antibiotic had a significant effect on the development of sucrase (sucrose α-D-glucohydrolase; EC 3.2.1.48), lactase (β-D-galactoside galactohydrolase; EC 3.2.1.23) and tripeptidase (EC 3.4.11.4) activities before weaning but had no effect on depeptidase (EC 3.14.13.11) activity. The study of the distribution of enzyme activity along the small intestine showed significant differences between the proximal and distal sections associated with weaning.

The availability of lysine and the ileal digestibility of amino acids in three cottonseed meals and a soya-bean meal for grower/finisher pigs were determined. The usefulness of the availability estimates for formulating diets was assessed. The availability of lysine, as assessed with a slope-ratio assay, was (proportion of total): cottonseed meal no. 1, 0.27; no. 2, 0.30, no. 3, 0.29; soya-bean meal, 0.90. Heal digestibility of lysine in the meals (proportion of total) was: cottonseed meal no. 1, 0.58; no. 2, 0.68; no. 3, 0.72; soya-bean meal, 0.89. Pigs given diets formulated to the same available lysine concentration grew at similar rates and retained the same amount of lysine in the carcasses. The results indicate that, for meals of high availability (soya-bean meal), reduced ileal digestibility appears to be the main reason for reduced availability. However, in meals of low availability (cottonseed meal), reduced ileal digestibility only accounts for part of the reduced availability. Thus, the ileal digestibility of lysine is not a reliable indicator of lysine availability.

The kinetics of urea metabolism were measured in children recovering from severe malnutrition. For a period of up to 10 d they received one of four diets which provided 711 kJ (170 kcal)/kg per d. Two groups received a diet with a high protein: energy (P:E) ratio of 10.6% (HP), enriched with either fat (HP/F) or maize starch and sucrose (HP/C). Two groups received a diet with a low P:E ratio of 8.8% (LP), enriched with either fat (LP/F) or maize starch and sucrose (LP/C). The rate of weight gain on the HP diets was significantly greater than on the LP diets. There was no difference in urea production between any of the four diets: HP/F 1.23 (SE 0.12), HP/C 1.37 (SE 0.14), LP/F 1.64 (SE 0.22), LP/C 1.15 (SE 0.15) mmol nitrogen/kg per h. On the HP diets urea excretion was 0.77 (SE 0.07) mmol N/kg per h. 61 % of production. There was significantly less urea excreted in the urine on diet LP/C than on LP/F (0.36 (SE 0.05) and 0.64 (SE 0.04) mmol N/kg per h respectively). A significantly greater percentage of the urea production was hydrolysed on the LP diets (61 %) compared with the HP diets (39 %), with the consequence that 50% of urea-N produced was available for synthetic activity on the LP diets compared with 30% on the HP diets. The increase in the urea hydrolysed on the LP diets was equivalent in magnitude to the decreased intake of N, so that overall intake plus hydrolysis did not differ between the LP and the HP diets. Crude N balance was similar on diets HP/F, HP/C and LP/C, but was significantly reduced on diet LP/F. These results show that there is an accommodation in urea kinetics during rapid catch-up weight gain, which becomes evident when the P:E ratio of the diet falls to 8.8%. It is proposed that, for a P:E ratio of 8.8%, protein is limiting for catch-up growth. When the intake has a P:E ratio of 8.8% the pattern of urea kinetics can be modified by the relative proportions of fat and carbohydrate in the diet. The measurement of urea kinetics provides a useful approach to the definition of the adequacy of the protein in the diet.

Breath hydrogen excretion was measured in eight lactase (EC 3.2.1. 108)-deficient volunteers ingesting 18 g lactose in the form of milk, yoghurt and heated yoghurt. Total excess hydrogen excretion (area under curve) was significantly lower after yoghurt and heated yoghurt, than after milk: 103 (SE 29), 191 (SE 32), and 439 (SE 69) respectively (P < 0.001). The oro-caecal transit time of fermentable components from yoghurt and heated yoghurt (mainly lactose) was longer than that from milk: 165 (SE 17), 206 (SE 19), v. 103 (SE 19) min (P < 0.01). An intestinal perfusion technique was used in the same subjects after ingestion on two consecutive days of 18 g lactose in yoghurt and heated yoghurt. Significantly less lactose was recovered from the terminal ileum after yoghurt than after heated yoghurt meals: 1740 (SE 260) v. 2825 (SE 461) mg (P < 0.05), and approximately one-fifth of the lactase activity contained in yoghurt reached the terminal ileum. These findings indicate that more than 90% of the lactose in yoghurt is digested in the small intestine of lactase-deficient subjects and suggest that both the lactase activity contained in the viable starter culture and a slow oro–caecal transit time are responsible for this excellent absorption.

Two experiments were conducted to determine the utilization of ileal digestible lysine by pigs. In the first, the apparent ileal digestibility of amino acids in cottonseed meal, meat-and-bone meal and soya-bean meal was determined in pigs fitted with‘T'-shaped cannulas. In the second experiment, three lysine-deficient diets were formulated to 0.36 g ileal digestible lysine/MJ digestible energy (DE), with lysine contributed from the three protein concentrates as the only source of lysine in sugar-based diets. An additional three diets were formulated with supplements of lysine to verify that lysine was limiting in the first three diets. The growth performance and retention of lysine by pigs given the six diets over the 20–45 kg growth phase were then determined. The apparent ileal digestibility of lysine in the three protein concentrates (proportion of total) was: cottonseed meal 0.74, meat-and-bone meal 0.78, soya-bean meal 0.89. Growth rates (g/d) of the pigs given the three diets formulated to 0.36 g ileal digestible lysine/MJ DE were significantly different (P < 0.001): cottonseed meal 377, meat-and-bone meal 492, soya-bean meal 541. The response of pigs to the addition of lysine confirmed that lysine was limiting in these diets. Crude protein (nitrogen× 6.25) deposited by the pigs was significantly higher (P < 0.001) for those given soya-bean meal (77 g/d), relative to meat-and-bone meal (66 g/d) and cottonseed meal (38 g/d). The proportion of ileal digestible lysine retained by pigs given the three protein concentrates was: cottonseed meal 0.36, meat-and-bone meal 0.60, soya-bean meal 0.75. The results indicate that values for the ileal digestibility of lysine in protein concentrates are unsuitable in dietary formulations as the assay does not reflect the proportion of lysine that can be utilized by the pig. It appears that, with heat-processed meals, a considerable proportion of the lysine is absorbed in a form(s) that is (are) inefficiently utilized.

Dietary nitrate and nitrite may affect colonic pathophysiology. These anions influence fermentation, and nitrite has been shown to augment sodium absorption by the colon and participate in the formation of N-nitroso compounds. There is, however, no general agreement as to how much dietary nitrate and nitrite reaches the colon. To help resolve this question, balance studies were performed on six healthy ileostomy subjects who were given diets that varied in nitrate content from 0.83 to 5.20 mmol/d. Nitrate and nitrite excretion in ileal effluent and urine were measured by anion-exchange chromatography with conductivity detection. There was no significant nitrite in the diets, urine, or ideal effluent. Dietary nitrate was largely excreted in urine (1.31–4.25 mmol/d). The urinary excretion findings indicated net synthesis of nitrate at low dietary intakes and net catabolism of nitrate at high intakes. Nitrate losses in ileal effluent were very low (0.03–0.05 mmol/d, 0.03–0.06 mmol/kg) and unrelated to intake for all the diets. It is concluded that dietary nitrate and nitrite do not enter the colon from the small intestine in amounts that would affect fermentation and mucosal metabolism in man. The possibility of significant amounts of nitrate reaching the colon via blood in normal subjects has not been excluded.

A method has been developed based on stable isotopes and biopsy procedures which allows the large-dose procedure for measurement of protein synthesis to be applied in serial studies to farm species. Measurements of total nitrogen retention and protein synthesis in m. longissimus dorsi and m. vastus lateralis were made in five wether lambs (40–44 kg) infused intravenously, successively, with vehicle (10 d); testosterone (15 d; 9 mg/d); vehicle (15 d). N retention was improved by testosterone infusion (+2.9 g N/d; a 96% improvement total over control periods). Muscle protein synthesis was not significantly altered by exogenous hormone administration, nor were RNA:protein, RNA:DNA or protein: DNA. The implication of the developed procedure for dynamic studies in accessible tissues of large animals is discussed.

Diets were formulated using sugar, soya-bean meal and free amino acids to contain 0.1–0.8 lysine/MJ digestible energy (DE) and offered at three times maintenance to male and female pigs from 20 to 45 kg live weight. Growth responses and retentions of protein, fat, energy and lysine were assessed. Increasing the dietary lysine concentration resulted in significant (P < 0.001) linear and curvilinear increases in growth rates and decreases in food conversion ratios. There was only a small effect of lysine concentration on total energy retention, but a substantial effect on the partitioning of energy deposition, with increases in the rate of protein deposition and decreases in fat retention. There was no difference in the efficiency of protein deposition between male and female pigs but males responded more to higher lysine concentrations than females (estimated 0.93 and 0.74 g lysine/MJ DE for males and females respectively). Lysine concentration in the protein deposited by the pigs increased linearly and curvilinearly (P < 0.01) from 5.8 to 6.6 g lysine/16 g N with increasing dietary lysine concentration. There was a linear and quadratic response (P < 0.001) in retention of ileal digestible lysine, with the minimum retention of 0.16 occurring at 0.1 g lysine/MJ DE and increasing to a maximum retention of 0.73 at a dietary concentration of 0.47 g lysine/MJ DE. The efficiency of lysine retained/ileal digestible lysine intake was 0.86 and the endogenous lysine loss was estimated at 0.94 g/d.

The effects of insulin on the utilization of propionate in glucose synthesis were studied in fed and fasted sheep. Insulin was infused at 0.04 μ/h into the mesenteric vein. Glucose was infused to prevent hypoglycaemia. The rate of incorporation of [2-14C]propionate into glucose was determined before and during insulin infusion. After 150 min of insulin infusion endogenous glucose synthesis was about 70% of control values, whereas the incorporation of [14C]propionate into plasma glucose was 94% of control values. In contrast, the incorporation of other glucose precursors into glucose was decreased 30–50% by insulin. Therefore, insulin does not appear to decrease the utilization of propionate in gluconeogenesis. These results are consistent with the proposition that insulin differentially affects the rate of incorporation of glucose precursors into glucose in ruminant animals.

The present study was designed to investigate whether 3 d of high-fat, low-carbohydrate diet (with normal daily energy intake) affected the metabolic, cardiovascular and thermic responses to an oral glucose load (1.5 g/kg body-weight). Eight normal weight, healthy subjects (five male) consumed diets containing approximately 65 % by energy of carbohydrate (C) or fat (F), each for 3 d. Before and after glucose ingestion, continuous recordings of oxygen consumption and carbon dioxide production were made using indirect calorimetry, and metabolic rate (MR) and respiratory exchange ratio (RER) were calculated. Heart rate, blood pressure and limb blood flow were also measured. There was no significant change in baseline MR following the high-fat diet, but the fasting RER was reduced. The high-fat diet modified the responses to oral glucose, with a greater increase in MR (kJ/min; C + 0.38, F + 0.76), and an enhanced plasma insulin response (mU/l; C + 51.5, F + 85.0). There were no differences between the two diets with respect to the baseline blood glucose levels or the changes after glucose ingestion. Heart rate, systolic and diastolic blood pressures and blood flow responses to the glucose load were similar after the two diets. There was no plasma catecholamine response to glucose ingestion. It can be concluded that a high-fat diet alters the initial thermic response and insulin response but does not alter the other physiological responses to glucose ingestion.

The effect of feeding v. fasting, on tissue blood flow, oxygen uptake and proportional contributions of the portal drained viscera (PDV), liver (Expts 1 and 2) and hindquarters (HQ; Expt 2) to whole-body O2 uptake were studied in beef steers. The combined techniques of indirect calorimetry and net tissue flux, the latter being the product of arterio-venous concentration difference and blood flow, were used in the experiments. In response to fasting, whole-body O2 consumption decreased as did O2 uptake by all measured tissues except the liver (trend only in Expt 1). Blood flow to all measured tissues decreased during fasting and fractional uptake of O2 decreased in PDV and increased in liver and HQ (Expt 2). Proportional contribution of specific tissues to whole-body O2 uptake changed when animals were switched from the fed to the fasted state. The percentage consumed by PDV decreased from 25.4 to 19.9, by liver increased from 20.5 to 26.4 and by HQ was unchanged (9.6 and 10.5) in Expt 2. These significant responses in Expt 2 were observed as trends in Expt 1. The changes in proportional contribution of tissues to whole-animal O2 uptake reflect the changing metabolic role of specific tissues to lack of food supply. These findings emphasize the central role of the liver in metabolism and indicate that fasting (catabolic) measurements may not reflect the previous fed (anabolic) physiological state.

The impact of alcohol (ethanol) on resting energy expenditure of male non-obese volunteers was determined in two studies. In the first study the thermic effect of alcohol on resting metabolic rate (RMR) was assessed in ten male non-obese volunteers. In the second study the impact of alcohol on diet-induced thermogenesis (DIT) was determined in twelve male non-obese volunteers. Energy expenditure was measured with a ventilated-hood system. RMR was measured for 60 min with the subjects in a fasting state. In the first study subjects received in random order 20 g alcohol in concentrations of 75, 180 and 300 ml/I water respectively. After measurement of the RMR the thermic effect of alcohol was measured for 90 min. In the second study volunteers received in random order and in duplicate either a meal of food (2 MJ) plus an alcoholic aperitif (20 g alcohol in a 180 ml/1 solution) or an isoenergetic meal of food alone (2.55 MJ) plus a placebo aperitif containing no alcohol. DIT was measured for 240 min. Alcohol induced a significant thermic effect, which varied between 0.22 and 0.30 kJ/min. No systematic difference in DIT was observed among the different concentrations. DIT was not significantly affected by the ingestion of alcohol. Total DIT was 219 (SE 14) kJ for the alcohol treatment and 185 (SE 20) kJ for the control treatment. The results do not support the suggestion that alcohol is less efficiently used as an energy source in comparison with, for example, fats and carbohydrates.

The influence of a change of colonic availability of biotin on biotin status was studied. This was done by inhibition of biotin absorption by intracaecal avidin infusion. Five adult minipigs with a permanent caecal ‘T’ cannula were fed on a semi-synthetic, biotin-deficient diet for 4 months. Following an 8-week adaptation period there were nine sequential 1-week infusion periods with or without oral lactulose or antibiotics. Avidin infusion during weeks 2, 5 and 8 amounted to 18 mg/d (13 U/mg). Plasma biotin concentrations were not changed by avidin infusions. There was a significant average 84% rise in faecal biotin excretion during the avidin periods. Urinary biotin output following avidin decreased by 21 %. This is taken as evidence that biotin synthesized by colonic bacteria is available for host metabolism. A rough estimate shows that under basal conditions 1.7–17% of the metabolic allowance may be covered by this metabolic route.

Six healthy non-obese male subjects were given three test meals containing 100 g carbohydrate and 1.5 g soluble paracetamol, supplemented on one occasion with 10 g guar gum and on another with 10 g sugarbeet fibre. A further six subjects were given the same test meal supplemented on one occasion with 10 g soya-bean-cotyledon fibre and on another, 5 g glucomannan. Venous blood samples were taken before, and at intervals for 180 min following the meal, and analysed for insulin, gastric inhibitory polypeptide (GIP) and paracetamol (as an index of gastric emptying). Arterialized blood samples were taken and analysed for glucose. Meal supplementation with both guar gum and sugar-beet fibre improved glucose tolerance, but circulating glucose levels were unaffected by the addition of either soya-bean-cotyledon fibre or glucomannan to the meals. Supplementation with guar gum and glucomannan lowered post-prandial insulin levels. Insulin levels were enhanced by addition of soya-bean-cotyledon fibre to the meal and unaffected by sugar-beet fibre. Post-prandial GIP levels were lowered in the guar–gum–supplemented meal and augmented with sugar-beet fibre supplementation. Addition of glucomannan and soya-bean-cotyledon fibre did not affect circulating GIP levels. The study failed to confirm previous reports of improved glucose tolerance following glucomannan and soya-bean-cotyledon fibre supplementation. The failure of sugar-beet fibre to reduce post-prandial insulin secretion despite improved glucose tolerance may be due to the observed increased secretion of GIP. The increased insulin levels seen following soya-bean-cotyledon fibre supplementation cannot be attributed either to changes in glucose tolerance, GIP secretion or gastric emptying.

The changes in the activities of the two vitamin B12-dependent enzymes methylmalonyl-CoA mutase (EC5.4.99.2) and methionine synthetase (5-methyltetrahydrofolate–homocysteine methyltransferase, EC 2.1.1.13) are described in two groups of sheep maintained for 20 weeks on either a cobalt-deficient or a Co-sufficient whole-barley diet. At the end of that period, the plasma concentrations of vitamin B12 were depressed and those of methylmalonic acid were raised in the Co-deficient group. During the course of the experiment hepatic holo-mutase activity, measured on biopsy samples, declined in Co-deficient animals with a half-life of 73 d. There was a similar, but slower decline in lymphocyte holo-mutase activity which fell with a half-life of 125 d. At slaughter, there was no difference between Co-sufficient and Co-deficient animals in total mutase activity in liver, kidney, brain and spinal cord. In contrast, the total-synthetase activity of liver and kidney was reduced by 60 and 30% respectively in the Co-deficient animals. There was no change in either group of animals in total-synthetase activity, or in either holo-mutase or holo-synthetase activity, in brain and spinal cord. In the Co-deficient animals, holo-mutase and holo-synthetase activities in liver, the tissue with the greatest activity of both enzymes, fell to 25 and 39% respectively, of that of Co-sufficient animals. The corresponding reductions for kidney were 12 and 51 % respectively. These results indicated that activity of both holoenzymes is greatly reduced in Co-deficient sheep.

The effect of underfeeding for 7 d (at 60 kJ/kg ideal body-weight) on the thermic and physiological responses to glucose and insulin infusions (hyperinsulinaemic euglycaemic clamp) was studied in six healthy women. Underfeeding had no significant effect on baseline metabolic rate, heart rate, forearm blood flow, diastolic blood pressure, blood intermediary metabolites, plasma insulin or catecholamines, but reduced both respiratory exchange ratio (RER; control (C) 0.86 (SE 0.02), underfed (U) 0.75 (SE 0.01) P < 0.01) and systolic blood pressure (by approximately 10 mmHg, P < 0.01). Baseline forearm glucose uptake and oxygen consumption were similar in both states. During the final 30 min of the glucose and insulin infusion, metabolic rate rose by 0.43 (SE 0.05) kJ/min in the C state, but no rise was seen in the U state (P < 0.01). Glucose disposal rate (C 47.9 (SE 1.8), U 47.3 (SE 4.1) μmol/kg per min) and storage rate (C 27.5 (SE 2.4), U 31.6 (SE 3.6) μmol/kg per min) were similar in both states, but glucose oxidation rate was reduced in the U state (C 20.5 (SE 1.7), U 15.4 (SE 0.7) μmol/kg per min; P < 0.05). RER rose to a higher value in the C state than in the U state (C 0.97 (SE 0.2), U 0.80 (SE 0.01); P < 0.01). During hyperinsulinaemia, the forearm glucose uptake and O2 consumption rose in both states. No significant differences were seen in the cardiovascular responses to hyperinsulinaemia in either state. Thus underfeeding abolishes the rise in thermogenesis and reduces glucose oxidation during glucose and insulin infusions in healthy women, but does not affect the glucose disposal or storage rates or the other measured responses.

Total testosterone (T), total oestradiol (E2) and sex hormone-binding globulin (SHBG) concentrations were measured in plasma samples from fifty-one male vegans and fifty-seven omnivores of similar age. Free T concentration was estimated by calculation, in comparison with the omnivores, the vegans had 7% higher total T (P = 0.250), 23% higher SHBG (P = 0.001), 3% lower free T (P = 0.580), and 11% higher E2 (P = 0.194). In a subset of eighteen vegans and twenty-two omnivores for whom 4 d diet records were available, there were statistically significant correlations between T and polyunsaturated fatty acids (r 0.37), SHBG and fat (r 0.43 for total fat, 0.46 for saturated fatty acids and 0.33 for polyunsaturated fatty acids), and SHBG and alcohol (r–0.39). It is concluded that a vegan diet causes a substantial increase in SHBG but has little effect on total or free T or on E2.

A two-pool model of tritiated water kinetics was used to estimate the major body water pools, and hence body composition, in goats at days 10, 38 and 76 of lactation. Between days 10 and 38 of lactation goats were, on average, in negative calculated energy balance and were estimated to have mobilized 59 g body fat stores/d. Mean calculated energy balance over days 38–76 of lactation was slightly positive and there was little change in estimated body fat. Gut fill increased over the early part of lactation when goats were mobilizing body fat. Consequently, live weight did not differ at any stage of lactation and did not provide a good index of body fat status of the goats. There were also no significant differences in empty-body-weight, water, protein, ash or fat-free mass at the three stages of lactation. As average calculated energy balance and changes in energy stored as fat were highly correlated, it is concluded that the two-pool model of tritiated water kinetics is a useful means of serially estimating changes in body fat content in unfasted lactating goats.