1. A new method has been used to measure mean gastric transit time.

2. This method, based on the absorption of 24Na from the proximal small bowel, is simple, non-invasive and can be used at the bedside.

3. The mean transit time was increased by adding guar gum to a test meal.

4. There was a significant correlation between mean gastric emptying time and a subjective measure of satiety.

1. It was shown that the water-soluble fraction of cow's milk and human milk did no possess significant antirachitic activity on rats.

2. Whole cow's milk was found to contain 38 i.u. vitamin D/1. Whole human milk contained 15 i.u. vitamin D/1, of which 12 i.u. derived from the lipid fraction.

3. Thus the values found were much lower than the 204 i.u./1 in cow's milk and 950 i.u./1 in human milk given in the literature based on chemical determination of the sterol sulphate content.

1. Energy balances were performed on sixteen low birth weight preterm infants over 7–10 d periods on a standard low-solute infant formula (2600 kJ/l), and on four high-energy formulas, providing different energy densities up to 3760 kJ/l. In two of the high-energy formulas the additional fat energy was provided by peanut oil, and in the other two by medium chain triglycerides (MCT). Anthropometric measurements and metabolic rate (MR) determinations were made during the balance periods.

2. Mean energy retention on the standard formula was 66% of the intake and declined to below 50% on the two feeds providing the highest energy. Extensive energy balance data on the standard formula are available for reference.

3. Net absorption of dietary energy increased on all the high-energy formulas, rising from 362 kJ/kg per d on the standard formula to 453 kJ/kg per d on the highest energy-formula (P < 0.001). There was no advantage in using MCT.

4. Net absorption of dietary energy improved with advancing maturity, irrespective of the formula.

5. In spite of the increased dietary energy retention, there was no increase in growth rate during periods of feeding with the high-energy formulas.

6. Fasting and postprandial MR increased by 10.4 and 12.8% respectively on the highest energy feeds.

7. It is concluded that, at least in the short term, this type of high-energy feeding increases MR at the expense of growth and thus is probably of no advantage to the infant.

1. Studies on the effect of supplementing copper and cobalt were conducted in 4- to 10-month-old dairy calves during successive indoor and outdoor feeding periods on conserved forges and fresh pastures respectively.

2. No significant differences in live-weight gains or serum Cu were recorded during the indoor period of 40 d.

3. Both live-weight gains and serum Cu were significantly elevated (P < 0.05) by Cu supplementation during the following grazing period of 70 d.

4. Supplementation with Co alone had no effect on any of the measurements taken, but it had an additive effect on weight gains to Cu supplementation during the grazing period.

5. It is concluded that Cu deficiency at marginal level is prevalent in the Mbeya area of Tanzania and that this is due to low Cu and high molybdenum in herbage.

1. Four mature Friesian cows were used. For 2 weeks after calving they were fed 3 kg hay (147 g crude protein (nitrogen × 6·25; CP)/kg dry matter (DM)) plus 9 kg concentrates (177 g CP/kg DM) per d and thereafter 4 kg hay plus 12 kg concentrates/d.

2. At approximately the 2nd, 4th and 9th weeks post-partum each cow was given a single intravenous dose of [14C]urea (1 mCi) and [6-3H]glucose (1·5 mCi). Following this, jugular venous blood samples were withdrawn up to 26 h post-injection.

3. The log (specific activity) v time curves were not linear for either metabolite. Glucose irreversible loss rates (IRL) were calculated by a stochastic procedure. The linear part of the urea log (specific activity) v. time curve gave the same estimate for urea IRL rate as a stochastic method of calculation, but urea pool sizes were overestimated so that stochastic analysis of results was preferred.

4. Mean milk yields at the time of the three measurements were 27·1, 30·8 and 27·9 kg milk/d.

5. Urea IRL was significantly lower (P < 0·05) in the first 4 weeks of lactation than in the 9th, and blood urea concentration was lower (P < 0·05) in the 4th than in the 2nd and 9th week, but there was no close correlation between urea IRL and concentration.

6. Glucose IRL rose (P < 0·05) between the 2nd and 9th weeks post-partum, perhaps due to the increase in feed intake. The results were generally consistent with the relationship between milk yield and glucose IRL established by Paterson & Linzell (1974).

7. Urea IRL (y) and milk protein-N (x) production values were used to calculate the efficiency of protein utilization (EPU) as x ÷ (x + 0·35 y). This assumes that 0·35 of urea IRL was due to protein catabolism. EPU was found to be 0·59–0·80 (mean 0·69).

8. The possible contribution of catabolized amino acids to glucose IRL was calculated by assuming that 0·35 of urea IRL was due to protein catabolism and 0·2 of catabolized protein-C passed through the glucose pool. On this basis the contribution of protein-C to glucose-C was < 25 g/kg glucose IRL.

1. The fatty acid composition of milk fat of Coopworth sheep offered varying pasture allowances has been determined after 1, 14 and 35 d of lactation. Differences in fatty acids occurred, particularly between 1 and 14 d, with a major increase in C18:0 whilst C16:0, C14:0 and C18:3 showed decreases.

2. When pasture allowances were restricted there were decreases in the short-chain fatty acids from C6 to C14 and an increase in C18:1 as has been observed previously for cattle. The C18:1:C10 value is a convenient measure of these changes and can be determined more rapidly than determining all the lower fatty acids.

3. The increased demand for milk resulting from suckling twin lambs caused an increase in C18:1 and decreases in C10 and C12 due to an increased utilization of body reserves.

4. The level of linoleic acid was much greater than has been previously observed in sheep given hay and contributes to the rapid rise in linoleic acid levels in lambs born under grazing conditions.

1. Pigs were fed on semi-purified food. The magnesium content of the experimental diet was 1·0 and that of the control diet 1·9 g/kg.

2. In the low-Mg group serum triglycerides and blood lactate values were increased and base excess and standard bicarbonate values were decreased, indicating metabolic acidosis.

3. A significant positive dependence was found between blood pH and serum Mg:Ca value as well as between blood pH and serum Mg, and also between body temperature and blood lactate values in the low-Mg group. None of these dependences was significant in the control group with magnesium acetate supplementation in the food.

4. No specific histopathological changes were found in heart, liver or kidney of the experimental animals.

5. The results indicate that an increase in serum triglycerides does not need to depend on the amount or quality of food fat.

6. The present study shows that, in pigs, a low-Mg diet may cause metabolic disturbances in instances when the food Mg content is distinctly higher than the normal values recommended by the (UK) Agricultural Research Council (1966) and (US) National Research Council (1968).

1. Growing rats were fed either ad lib. or with six (equal) meals offered every 4 h (form 10.00 hours). Rats of each group were killed at intervals of 4 h begining at 11.00 hours. Activities of cathepsin A (carboxy-peptidase A; EC 3.4. 12. 2), C (dipeptidyl peptidase; EC 3.4.14.1) and D (endopeptidase D EC 3.4.23.5) were measured in liver and muscle homogenates and free amino acids in blood were determined.

2. In the rats fed ad lib. activities of carboxypeptidase A and endopeptidase D in liber and muscle showed significant variation, with maximum activity in the light period. In general, meal-feeding only caused minor differences in cathepsin activities; although significant differences occurred for carboxypeptidase A. For the latter enzyme a peak in activity occurred in the dark as well as in the light period.

3. Irrespective of the feeding schedule, the lower concentration of free essential amino acids of blood occurred generally during the night period. With the controlled-feeding schedule there is an increase of essential amino acids and a slight decrease of non-essential amino acids of blood.

1. Romney wethers were infused intravenously with [2-14C]acetate for 5 d during which time they were given, three/group, different amounts of lucerne(Medicago sativa L.) chaff. The groups and the amounts fed were: MS, 700 g but starved during the infusion period; M, 700 g throughout; 1.3 M, 950 g throughout; AL, ad lib. throughout.

2. On day 4 of the infusion, the oxygen consumption, and production rate of expired 14CO2 were measured. At the end of the infusion, the sheep were killed and the amounts of radioactivity in the lipids of various tissues wre determined.

3. Significant differences were present between the specific activities of the tissues. The internal adipose tissues generally had higher specific activities than subcutaneous or intermuscular adipose depots. Although the intramuscular lipid also was highly labelled, the liver had the greatest specific activity.

4. Food intake did not significantly affect this pattern of specific activity of labelling of the tissues.

5. While most of the total lipid radioactivity was present in adipose tissues, the proportion in the liver increased to 40% during starvation.

1. The effects of restricted feeding, and ad lib. feeding following food restriction, on hepatic carbohydrate and lipid metabolism in the laying hen were studied.

2. The birds were allocated to four groups and given either 92, 84 or 75 g/d or allowed ad lib. access to food.

3. Food restriction significantly reduced liver total lipid content compared with ad lib.-fed control birds and this was reflected in reduced hepatic lipogenic enzyme activities.

4. When birds from the restricted regimens were allowed free access to food they intially consumed more food than the control group but after 2 weeks of ad lib. feeding the food consumptions of the birds in all the groups were similar.

5. Concomitant with the increase in food intake there were also increases in liver lipid content and hepatic lipogenic enzyme activities. After 18 d of ad lib.feeding these measurements were similar in the previously restricted birds and the ad lib.-fed control group.

6. Despite these effects on lipid metabolism, food restriction, and the subsequent release from food restriction, had no significant effects on the specific activities of the glycolytic enzymes examined.

7. Although there were large increases in liver lipid content following release from feed restriction no birds died from, or showed any of the symptoms of, fatty liver-haemorrhagic syndrome. This suggests that, in the absence of any other factor which may be involved in the syndrome, these high liver lipid contents were not, alone, sufficient to cause FLHS. The results also indicate that free access to food following food restriction is unlikely to be a major factor in initiating the syndrome.

1. Five groups of rats were investigated: (a) unmated rats allowed free access to a commercial stock rodent diet (NP group); (b) rats in the second week of lactation allowed free access to the stock diet; (c) rats in the second week of lactation allowed only that amount of the stock diet eaten by the NP group; (d) rats in the second week of lactation allowed that amount of the stock diet eaten by the NP group and in addition free access to a high-energy, protein-free supplement; (e) rats in the second week of lactation allowed that amount of the stock diet eaten by the NP group and in addition free access to a protein supplement.

2. The weight and length of the small intestine, the mucosal content of protein and of DNA and the mucosal activities of alkaline phosphatase (EC 3.1.3.1), acid phosphatase (EC 3.1.3.2), isocitric de- hydrogenase (NADP+)(EC 1.1.1.42)and glucose-6-phosphatase (EC 3.1.3.9) were measured in individual animals.

3. For the factors investigated it was, with few exceptions, found that: there were markedly higher values in lactating animals allowed unrestricted access to food than in unmated animals; in restricted lactating animals the values were considerably lower than in unrestricted lactating rats and often similar to those in unmated animals; supplements of dietary energy restored none or only a proportion of the in- creases usually found in lactation but a protein supplement restored most or all these increases. Reasons for departure from this general picture on the part of some factors are discussed.

4. The results presented here support the view that changes found in lactation are hormonally induced but governed by nutrient availability, that protein is the important nutrient raw material but that dietary energy can support some changes probably by a ‘protein-sparing’ effect. Some changes appear to be less susceptible to the effects of dietary restriction, whether of protein or total energy. It is suggested that the additional nutrients eaten by unrestricted lactating rats permit the development of more, but less mature, enterocy tes.

1. Nucleic acids and breakdown products were estimated in digesta taken from different sites in the small intestines of slaughtered steers given different diets. Amounts passing different sites were compared using cellulose as a non-digestible marker. The validity of this marker was checked with chromic oxide in some experiments. In other experiments, nucleic acids or derivatives were infused into the proximal duodenum of steers receiving diets of approximately equal proportions of flaked maize and hay. The amounts disappearing during passage through the small intestine were estimated using polyethylene glycol (PEG) as a non- absorbable marker.

2. In the slaughter experiments the amounts of nucleic acids entering the small intestine varied with the type of diet. RNA and DNA disappeared on average, to extents of 89% and 80% respectively between the abomasum and the terminal ileum, irrespective of the diet. RNA disappearance occurred almost entirely in the proximal quarter of the small intestine, whereas that of DNA extended further along the tract.

3. Nucleic acid degradation in the upper small intestine was accompanied by the transient appearance of adenosine, guanosine and pyrimidine nucleosides. These products were in greatest concentration in digesta from the first quarter of the small intestine and had generally completely disappeared by the terminal ileum.

4. Of the different substances infused into the small intestine, free nucleic acids were removed to extents greater than 97%, adenine, guanine and uracil had completely disappeared, thymine and xanthine to approximately 80% and 95% and hypoxanthine and cytosine to only 51% and 48% respectively. The nucleosides adenosine and cytidine were also completely removed in the small intestine but were replaced, in part, by the catabolic products inosine plus hypoxanthine or cytosine respectively. Other nucleosides were removed to approximately half the extent of the corresponding bases.

5. Serum and urine allantoin and uric acid levels were related to the amounts of purines entering the small intestines in free or bound form.