The effect of method of conserving grass herbage and the frequency of feeding on digestion in and passage from the rumen was studied in growing cattle. A single sward of perennial ryegrass (Lolium perenne cv. Endura) was cut on 1 d and conserved as silage or hay. These forages were offered as the only feed to twelve rumen-cannulated Friesian steers (average initial live weight (LW) 128 kg) either at a restricted level of intake (20 g dry matter (DM)/kg LW; Expt 1) or ad lib. (Expt 2). In Expt 1 the forages were offered either once or eight times daily. When fed once or eight times daily, in vivo digestibility of DM was very similar for hay and silage (0.771 and 0.783 respectively), while the fractional rate of digestion measured by incubation in Dacron bags was significantly (P < 0.05) higher for silage (0.069) than hay (0.057). The rate of passage of mordanted feed out of the rumen was significantly (P < 0.01) faster for silage when determined from concentrations of marker in the rumen (0.034 v. 0.028 /h). The volume of liquid in the rumen was lower (P < 0.01) for animals consuming silage (27.51) compared with hay (37.11), while the fractional rate of passage of liquid from the rumen was higher (0.141 v. 0.098 /h, P < 0.05). The volume of liquid in the rumen was also lower (P < 0.05) in steers offered feed eight times daily (29.51), compared with once daily (35.11), but frequency of feeding had no significant effect either on total digestibility or on rate of digestion in the rumen. The ad lib. intake of silage was significantly (P < 0.01) lower than that of hay (4.53 v. 5.16 kg DM/d) in Expt 2.

Current infant feeding guidelines recommend exclusive breast-feeding until the infant is about 4 months old to reduce the risks of early termination of breast-feeding, undernutrition and infection. In many societies, however, supplementary foods are given well before 4 months of age. The present paper describes weaning practices, factors associated with early supplementation and the effects of supplementation on duration of breast-feeding in a random sample of sixty northern Thai breast-fed infants studied prospectively from birth to 2 years of age. Composition of supplementary foods, energy and protein intake from supplements and changes in the supplementary diet with increasing infant age are also described. Rice-based foods were given from soon after birth; 81% of the sample had received supplements by 6 weeks of age. Early supplementary feeding was significantly associated with rural residence, large household size, maternal employment in agriculture and maternal age. Girls and infants with lower birth weights tended to be supplemented earlier. Despite early feeding of supplements, breast-feeding was prolonged, with median duration of 12 months. Early introduction of supplements and quantity of supplements consumed in the first 3 months were not associated with duration of breast-feeding. However, mothers who gave infant formula as the first supplementary food stopped breast-feeding slightly earlier, as did younger mothers living in households with more children.

Breast-feeding: Supplementary feeding: Weaning

The effect of vitamin C on the common cold has been the subject of several studies. These studies do not support a considerable decrease in the incidence of the common cold with supplemental vitamin C. However, vitamin C has consistently decreased the duration of cold episodes and the severity of symptoms. The benefits that have been observed in different studies show a large variation and, therefore, the clinical significance may not be clearly inferred from them. The biochemical explanation for the benefits may be based on the antioxidant property of vitamin C. In an infection, phagocytic leucocytes become activated and they produce oxidizing compounds which are released from the cell. By reacting with these oxidants, vitamin C may decrease the inflammatory effects caused by them. Scurvy, which is caused by a deficiency in vitamin C, is mostly attributed to the decreased synthesis of collagen. However, vitamin C also participates in several other reactions, such as the destruction of oxidizing substances. The common cold studies indicate that the amounts of vitamin C which safely protect from scurvy may still be too low to provide an efficient rate for other reactions, possibly antioxidant in nature, in infected people.

The influence of the method of conserving grass herbage and the frequency of feeding on eating behaviour, rumen motility and rumen fill was studied in growing steers. Silage and hay were offered to twelve rumen-cannulated Friesian steers (average initial live weight (LW) 128 kg) at a restricted level of intake (20 g dry matter (DM)/kg LW) either once or eight times daily. With once daily feeding, the daily intake of hay was consumed in a single large meal which lasted about 2 h, while silage was eaten in many small meals throughout the day. The proportion of the day spent ruminating was higher (0·39) for steers offered hay once daily than for those offered silage (0·28) or hay eight times per day (0·29). There was little effect of conservation method on frequency of rumen contraction, but contractile intensity (integration of frequency and amplitude) increased during the second half of the 24 h feeding cycle in steers offered hay either once daily or eight times daily, while the same effect was only observed when silage was offered once daily. Total daily contractile activity (the integration of the frequency and duration of myoelectric spike bursts) was significantly (P < 0·05) higher in steers offered hay, compared with silage, once daily. The mean weight of organic matter in the reticulo-rumen of steers offered hay was significantly higher than for silage both with once (1593 v. 1326 g organic matter (OM)/100 kg LW, P < 0·01) and eight (1367 v. 1160 g OM/100 kg LW, P < 0·05) times daily feeding. The proportion of the particulate pool which was present as small (< 1·2 mm) particles was always greater than 0·60.

The variation in the thermic effect of a meal (TEM) was investigated in two groups of five subjects following a standard test meal. Results demonstrated a 50 % lower response over 6 h, in the same subjects, when measured intermittently (protocol 2) as compared with a continuous measurement (protocol 1). The variation in TEM among occasions (measured on three occasions in each subject) was large (coefficient of variation (CV) 18.7%, P < 0.02). However, the post-meal total energy output (CV 1.4%, P > 0.05), non-protein respiratory quotient (CV 1.9%, P > 0.05) and substrate oxidation rate were not different (P > 0.05) in the same individual on separate occasions. Small variations in the basal metabolic rate (BMR) from occasion to occasion (CV 2.6%) contributed to the variation in TEM. However, after allowing for the changes in BMR, variation in TEM (CV 8.6%, P > 0.05) was still sizeable though not statistically significant.

Thermic effect: Methodology: Variation of thermic effect

As a basis for studies of the influence of lipids on the immune response and health, adult C57 BI mice were fed for 10 weeks or longer on one of the following diets: high (200 g/kg) polyunsaturated fatty acid, high (200 g/kg) saturated fatty acid and low (50 g/kg) polyunsaturated fatty acid purified diets and a standard commercial diet. The three test-fat diets were compounded to have approximately the same energy content and the mice of each group maintained similar body-weights. High-fat diets significantly reduced their subsequent delayed hypersensitivity response to challenge after sensitization with tuberculin. Immunoglobulin (Ig)M antibody formation against Escherichia coli lipopolysaccaride was transiently decreased, but IgG antibody against sheep erythrocytes and killed salmonella vaccine, IgG and IgE antibodies against ovalbumin remained unaffected. Total and differential blood counts revealed no differences between mice on high-fat and control diets in either the absolute numbers or the proportions of the types of leukocytes. Studies on peritoneal macrophages from mice of each group showed no difference in morphology and they ingested non-toxic and toxic particles releasing similar amounts of lactate dehydrogenase (EC 1.1.1.27) and β-glucuronidase (EC 3.2.1.31) for each substance, indicating that there were no differences in viability or phagocytic function. The present study shows that the C57 BI mouse can provide a model for the investigation of some consequence of the reduced immunocompetence induced by high-fat diets.

The thermic effect of a standard liquid meal (TEM; energy 2.5 MJ; containing (g/kg) protein 100, fat 150, carbohydrate 750; volume 350 ml) was measured in a chronically undernourished (UN; n 9) group of human subjects and was compared with results from two control groups, one normal weight (NW)-for-height (BMI > 20; n 10) and the other underweight (UW)-for-height (BMI < 18, n 10), using a ventilated-hood system over a period of 6 h after ingestion of the meal. Results indicated that the UN subjects had lower values for body-weight, height, percentage fat and fat-free mass (FFM) compared with those of either control group. Basal metabolic rates were lowest in the UN group in absolute terms; however, there were no significant differences among groups on an analysis of covariance (ANACOVA) with FFM as the covariate. TEM responses in the UN group were significantly higher when expressed either in absolute terms or as a percentage of the energy density of the meal. The post-meal total energy output was significantly lower (P < 0.05) in the UW and UN groups as compared with the NW group in absolute terms; however, on adjusting for differences in FFM (by ANACOVA) there were no significant differences among groups. This would suggest that in the chronically undernourished thermogenic responses to a meal are unlikely to contribute towards any energy saving and may not constitute a part of any adaptive response to the undernourished state.

Chronic undernutrition: Thermic effect: Substrate oxidation rates: Body composition

The effect of the α2-adrenergic agonist, guanfacin, on the energy metabolism, feed intake and live weight (LW) change of steers was studied in three experiments. In the first, the metabolic rate of twelve steers was measured after a 72 h fast. The next day, after a 96 h fast, six steers were injected intramuscularly with 15 mg guanfacin in sterile saline (9 g sodium chloride/l) and six with sterile saline alone, and metabolic rate was measured again. Treatment significantly (P < 0.01) lowered metabolic rate by approximately 20% (53.9 v. 66.8 kJ/kg per d). In the second experiment twelve steers were fed on long-chopped, low-quality roughage (Pangola grass (Digitaria decumbens) hay) ad lib. for 6 weeks. Six steers were continuously infused through a jugular catheter with 15 mg guanfacin/d (about 40 μg/kg LW) in sterile saline. The other six served as controls. There was no significant effect of treatment on feed intake (g dry matter (DM)/kg LW) or the rate of LW loss. Treatment significantly (P < 0.05) increased the retention time of fluid (17.9 v. 22.1 h) in the alimentary tract. In the final experiment twenty-three steers were divided into four treatment groups and fed on long-chopped, low-quality roughage (Pangola hay). Treated animals were continuously infused with guanfacin at the rate of 20, 40 or 80 μg/kg LW per d. Control steers were not infused. At the end of the 6-week feeding period metabolic rate was measured after a 72 h fast. Regardless of dose, guanfacin significantly (P < 0.01) lowered metabolic rate. Feed intake was not significantly affected by treatment but the rate of LW loss was significantly (P < 0.05) less in treated steers.

The present experiment was designed to study the effects of factors likely to alter microbial purine yield from the rumen on urinary excretion of allantoin-nitrogen (UAN). Sixteen mature Clun Forest–Welsh crossbred wethers were used in a 2 × 2 × 2 × 2 factorial design to investigate the effects of (1) level of intake, (2) wheat: nutritionally improved straw (NIS) ratio, (3) sodium bicarbonate inclusion and (4) monensin inclusion on diet digestibilities, fractional outflow rates of solids and liquids from the rumen and urinary allantoin excretion. Each treatment occurred in each of two experimental periods. The treatments were designed to influence microbial purine yield via changes in rumen outflow rate and microbial maintenance coefficient. Increasing the proportion of NIS and increasing feeding level decreased digestibility and increased the fractional outflow rate of solids. Increasing the level of intake increased the fractional outflow rate of liquids. Urinary allantoin excretion (/kg live weight0.75 per d) was significantly increased by an increased proportion of wheat in the diet and increased level of intake, and significantly reduced by NaHCO3. There was a significant interaction effect such that increasing level of intake did not increase UAN with the high-NIS diet, despite an increased fractional outflow of solids from the rumen, in contrast to the increase observed with the high-wheat diet. Taken together with other observations it is suggested that high sodium concentrations in the diet reduce the efficiency of microbial synthesis, probably by increasing the energy cost of maintaining osmolarity. Monensin had no overall effect on UAN but there were significant interactions between monensin and dietary Na; the inhibitory effect of monensin on UAN was eliminated or reversed in the presence of added NaHCO3. This is consistent with theories that monensin increases the net influx of hydrogen ions into microbial cells and that this influx can be reduced by increased extracellular sodium ions.

Five apparently healthy, chronically undernourished (UN) male volunteers aged between 18 and 30 years were studied before and after 12 weeks of dietary supplementation. The thermic effect of a meal (TEM) was measured over a period of 6 h using a ventilated-hood system. Results indicated a significant increase in body-weight after supplementation due to increases in body fat and fat-free mass (FFM) in the proportion of 69% and 31% respectively. The basal metabolic rates (BMR) measured post supplementation were significantly higher in absolute terms, with a trend towards higher values when adjusted for the changes in FFM. TEM responses measured after 12 weeks of supplementation were significantly lower when expressed either in absolute terms (presupplementation 227.0 kJ v. post supplementation 193.5 kJ), or as a percentage of the energy density of the meal (9.1% v. 7.7%). This lower TEM was reciprocal to the changes in the BMR (r −0.86). The post-meal total energy output (PMTEO) was, however, not significantly different after 12 weeks of dietary supplementation. The unchanged PMTEO would indicate an unaltered ‘thermogenic capacity’, following supplementation, in these chronically undernourished subjects. These results confirm our earlier conclusion that, in chronic undernutrition, the thermic response to a meal may not contribute to any energy saving.

Chronic undernutrition: Dietary supplementation: Basal metabolic rates: Thermic effect: Substrate oxidation rates

An in vitro method applying Michaelis–Menten saturation kinetics was developed as an alternative approach for estimating protein degradation rates in the rumen. Non-linear regression (NLR) analysis of the integrated Michaelis–Menten equation yielded fractional degradation rates, kd, from direct estimates of the maximum velocity: Michaelis constant ratio (kd = Vmax: Km). Degradation rates obtained using data from a series of 2 h inhibitor in vitro incubations were respectively 0.989, 0.134, and 0.037 /h for casein, solvent soya-bean meal (SSBM) and expeller soya-bean meal (ESBM). Degradation rates obtained from 2 h incubations had lower standard errors than those obtained using 1 h incubations; 2 h rates were not significantly different from 1 h rates, suggesting end-product inhibition was not significant at 2 h. The NLR Michaelis–Menten method was used to determine degradation rates for twelve protein sources: casein, bovine serum albumin, two samples of lucerne (Medicago sativa) hay, and four samples each of SSBM and ESBM. Statistical analysis of NLR results revealed significant differences among the twelve protein sources. Casein was degraded most rapidly (0.827 /h), and the four ESBM samples most slowly (0.050–0.098 /h). Degradation rate for serum albumin was 0.135 /h; rates for SSBM and lucerne hays ranged from 0.160 to 0.208 /h. Degradation rates estimated using the NLR method were more rapid than those obtained with a limited substrate approach; NLR rates were more consistent with in vivo estimates of rumen protein escape. Greater concentrations of slowly degraded proteins were needed with the NLR method to define curvilinearity of the degradation curve more accurately.

Protein degradation rate: Rumen protein escape: Michaelis–Menten kinetics: Non-linear regression

Heat production (HP) and the intake and retention of energy and nitrogen were measured in growing broiler fowl kept at 32° and given diets with metabolizable energy contents from 8 to 15 MJ/kg and crude protein (N × 6·25; CP) contents of 130 and 210 g/kg. The temperature of 32° was chosen for comparison with earlier measurements at 20° to minimize heat produced for the maintenance of body temperature. The effects of diet composition were observed when the same birds were taken from 20 to 32°. The tendency for energy intake to increase with dietary energy concentration was less at 32 than at 20°. The lower heat increments measured for the high-fat diets did not, therefore, confer an increased ability to sustain higher energy intake at 32°. HP was about 17% lower at 32 than at 20°; the change in HP between 20 and 32° was not significantly influenced by diet composition. The absence of significant effects of diet composition on HP, combined with the significant trend in energy intake, produced significant differences (related both to dietary energy and dietary protein concentrations) in total energy retention and in the partition of retained energy between protein and fat. As at 20°, variation in energy retention and in the composition of retained energy were the main responses to variation in dietary CP concentration and energy intake; a significantly higher energy cost of unit protein accretion on the low-CP diets was insufficient to produce an elevation in total HP because the higher unit energy cost was balanced by a lower absolute rate of protein accretion.

Utilization of three milk diets including cream, casein or whey, each naturally labelled with 13C (1 mmol 13C excess) from C4 sources, by six young male calves of the Deutsche Fleckvieh breed was investigated in a Latin-square split-plot design. Each milk diet was examined under resting conditions and during a short period of physical exercise on a treadmill. δ13C values (‰) in carbon dioxide in expired air were measured at intervals of about 1 h during 6·5 h after food intake. Expired air samples for CO2 isolation, subsequent isotopic analysis, measurement of CO2 production and respiratory quotient were taken at about hourly intervals and 13C recovery rates over 6·5 h were calculated. Feeding milk containing enriched milk casein, cream, or whey resulted in maximal significant 13C enrichments over background (δ13C) in CO2 of +1, +2·4 and +2·2‰, and recovery rates of 3·6, 9·9 and 12·2% respectively. This comparison shows the different kinetic behaviour of the main nutrients during the oxidation in tissues. The short exercise period (5 min at 1 J/s per kg body-weight + 5 min at 2 J/s per kg body-weight) did not influence the recovery rates significantly. However, after 10 min of muscular exercise there was a brief decrease in δ13C value of expired air which disappeared within the first 5 min of rest. These experiments demonstrate for the first time the applicability of the 13C breath test with naturally enriched diets in animal nutrition research and that quantitative results may be obtained.

Growing Friesian steers chronically catheterized in the anterior mesenteric and portal veins were used to study the influence of feeding with either a forage or forage–concentrate diet on nutrient utilization by mucosal tissue. When animals were consuming the forage–concentrate diet the molar proportion of propionate in rumen fluid was significantly increased, although production rate as measured by isotope dilution was not altered. Net rates of absorption of VFA into portal blood when compared with rumen production rates underlined the extent to which metabolism within mucosal tissue modifies the propionate supply to the liver. Net glucose utilization by splanchnic tissue was shown to be significantly lower on the forage–concentrate diet. There were no effects of diet on whole-body glucose turnover or on the proportion of glucose derived from propionate. Animals fed on the forage–concentrate diet had significantly lower concentrations of circulating essential amino acids, due mainly to a reduction in branched-chain amino acid levels. There was net absorption of all amino acids by animals on both diets except for glutamate, glutamine and taurine in forage-fed animals.

The present paper offers a dual 14CO2 breath test approach to study the metabolic utilization of free amino acids in the body. Using the carboxyl-[14C]isotopomer of an amino acid as the test substrate the percentage recovery of the isotope as 14CO2 reflects which part of the labelled amino acid flux has been decarboxylated. The residual C fragments may flow to total oxidation at least to the level recovered for the universal [14C]isotopomer. In the case that recovery for total oxidation is less than for decarboxylation, part of the [14C]fragments are retained in the body by either exchange or non-oxidative pathways. Utilization of tyrosine and leucine was measured in the post-absorptive phase in adult rats conditioned on isoenergetic diets containing 210, 75 or 0 g protein/kg. It was shown that the level of dietary protein exerts an influence on both decarboxylation and total oxidation. Although the responses of leucine and tyrosine were not different for total oxidation, there was a difference between the amino acids in their relative rate of decarboxylation. That this dual 14CO2 breath test approach can be used as a tool to evaluate whether the protein and amino acid supply has been adequate to support actual requirements is discussed.

Amino acid utilization: Amino acid requirements: Leucine: Tyrosine

To test whether the glycaemic index is altered by the amount of carbohydrate, meals containing 25 and 50 g carbohydrate as white rice and white bread were taken by seven non-insulin-dependent diabetic subjects. The glycaemic indices to parboiled white rice corresponding to 25 and 50 g carbohydrate were similar, being 55 (SE 10) and 60 (SE 8) respectively. The incremental areas of blood glucose (above basal) to parboiled white rice were significantly lower than to white bread after both an amount corresponding to 25 g carbohydrate (85 (SE 24) mM × 180 min v. 181 (SE 55) mM × 180 min; P < 0.01) and to 50 g carbohydrate 226 (SE 29) mM × 180 min v. 423 (SE 76) mM × 180 min; P < 0.01). Similar insulin response areas to 25 g carbohydrate given as parboiled white rice and white bread were found, whereas 50 g carbohydrate as white bread caused a significantly higher insulin response area than parboiled white rice (P < 0.05).

In conclusion, the glycaemic index of parboiled white rice is not affected by the amount of carbohydrate ingested, at least under the present study conditions.