1. A technique is described for the measurement of the extent of 65Zn absorption by different regions of the intestine in the intact rat. Using this technique it was shown that the duodenum contributed 60%, the ileum 30% and the jejunum 10% to the over-all absorption of 65Zn. Negligible absorption of 65Zn occurred from the caecum and colon.

2. Using ligated loops of rat duodenum in situ, 65Zn absorption was shown to be rapid, with 1% of a 5 μg dose being transferred to the carcase within 1 min of intraluminal dosing.

3. When 65Zn was injected into ligated loops in a dose range of 1–200 μg Zn/ml the rate of absorpion was linear with respect to time over the first 15 min. The rates of 65Zn absorption v. dose of 65Zn exhibited saturation kinetics indicating absorpion by a ‘carrier’ or enzyme-mediated process.

4. The binding of 65Zn to loop tissue showed biphasic kinetics which suggested that at low intraluminal concentrations of Zn (1–50 μg Zn/ml) binding was to specific sites whereas, at higher concentrations (50–200 μg Zn/ml), non-specific binding occurred.

5. A study of the fate of mucosally bound 65Zn showed that over the first 30 min a proportion of the 65Zn was rapidly transferred to the carcase and this was probably associated with the rapid phase of 65Zn absorption described previously. From 30 min up to 6 h after the initial binding, 65Zn was also transferred to the carcase albeit at a much slower rate indicating a slow phase of Zn absorption. A study of the kinetics of this slow phase indicated that the loss of bound 65Zn to the body was a saturable process indicating an enzyme or ‘carrier’-mediated process. A comparison of the kinetics of the slow and rapid phases of 65Zn absorption suggests that these processes are distinct.

6. Histological examination of mucosal tissue of loops exposed to 200 μg Zn/ml revealed no discernable damage. Similarly, no effect was observed on either arginine or glucose uptake by isolated duodenal loops in situ, although this concentration of Zn completely abolished fluid uptake. A study of the effect of different doses of Zn showed that 50 μg Zn/ml inhibited mucosal fluid uptake by more than 50% and 100 μg Zn/ml by more than 90%. It was concluded that these effects were due to a specific action on the fluid-transfer process and not due to a general poisoning of the mucosa.

1. A cereal-based diet containing 7.6 mg copper/kg was fed ad lib. to laying hens for up to 48 d. Four other groups were given the control diet to which was added hydrated copper sulphate to provide 250, 500, 1000 and 2000 mg added Cu/kg.

2. Hens were killed on day o and after 3, 6, 12, 24 and 48 d. Records were kept of body-weight, food consumption, egg production and egg weight.

3. After slaughter blood haemoglobin, packed cell volume, serum Cu and aspartate aminotransfferase- (AAT; EC 2.6. I. I) were measured. The liver, kidneys, a sample of breast muscle, oviduct, ovary and gizzard were weighed. Gizzard, spleen. liver and kidney tissue were examined histologically.

4. The Cu, zinc and iron concentrations of liver, kidneys and breast muscle and the manganese concentrations of liver and kidneys were determined.

5. Body-weight loss occurred at 500–2000mg added Cu/kg diet. Egg production was depressed by level of added Cu and period of time on the Cu-containing diets.

6. Mean liver, kidney, oviduct and ovarian weights per unit body-weight were depressed by Cu in the diet and the effect increased with period of time on the diets. Mean gizzard weight per unit body-weight was increased by dietary added Cu and by time.

7. Cu concentrations in the liver were increased by dietary level of added Cu and period of timeon the diet. Zn concentration in liver increased at 1000 and 2000 mg added Cu/kg diet and liver Fe concentration was increased at these levels. Histological examination of the gizzard indicated that the Cu content of the gizzard lining increased with dietary added Cu.

1. Twenty-eight male rats of initial age 27 d were fed on fortified-barley diets for 3 weeks. In all experimental diets, both crude protein (nitrogen × 6.25) and methionine:cystine were constant at 1200 g/kg dry matter (DM) and 2: 1 respectively. The basal diet contained 45 g methionine plus cystine/kg DM with L- methionine plus L-cystine (2: 1, w/w) added in increments of 0.5 g/kg DM to a final level of 70g methionine plus cystine/kg DM. A ‘positivecontrol’ diet of barley plus 193.7 g soya-bean meal/kg DM contained 6.0 g methionine plus cystine/kg DM.

2. Weight gain, food conversion efficiency (FCE), urinary urea-N excretion, carcass composition and activities of liver cystathionine synthase (EC 4.2.1.22) and N6-methyltetrahydrofolate-homocysteine-methyltransferase (EC 2.1.1.13) were determined.

3. Weight gain, food consumption, FCE and carcass composition measurements of rats showed either small or no differences between the experimental diets containing 4.5–7.0 g methionine plus cystine/kg DM. For the over-all period, weight gain and FCE of rats receiving the ‘positive control’ diet were significantly higher than values obtained with rats receiving any of the experimental diets.

4. Cystathionine synthase activity (μmol/mg protein per 60 min; units) increased from 13.38 at 4.5 g dietary methionine plus cystine/kg DM to 18.81 at 5.0 g dietary methionine plus cystine/kg DM. The activity was then inhibited to reach a minimum value of 10.16 units at the 6.0 g/kg DM dietary level. Thereafter the activity increased to a value of 3000 units at 7.0 g dietary methionine plus cystine/kg DM.

5. The activity of N5-methyltetrahydrofolate-homocysteine-methyltransferase was constant at 0.70 0.74 nmol/mg protein per 60 min between dietary levels of 4 5 and 5.0 g methionine plus cystine/kg DM. The activity then increased to a maximum value of 2.32 nmol/mgprotein per 60 min at the 6.0 g/kg DM level. Thereafter the activity decreased, reaching a minimum value of 0.70 nmol/mg protein per 60 min at the 7.0 g methionine plus cystine/kg level.

6. Urinary urea-N excretion decreased significantly from 1.07 g/kg DM intake at the 4.5 g dietary meth- ionine plus cystine/kg DM level to 1.05g/kg DM at the 5.0 g/kg dietary level, then dropped significantly to a level of 1.01–1.00/kg DM intake for the higher levels of dietary methionine plus cystine.

1. The purpose of the experiments was to determine certain properties of the metabolism of nitrogen compounds and carbohydrates in the rumen and tissues of growing bulls which were given either a diet containing sugar-beet silage, a urea-mineral preparation and hay or a control diet with maize silage, ground barley and hay. Daily rations were given in two equal portions twice daily at 07.00 hours and 13.00 hours. The experiment lasted 182 d.

2. The experimental diet containing 0.54 g urea and 5.0 g saccharose/kg body-weight did not cause any symptoms of toxicity in the animals although there were large changes in the concentration of metabolites in the forestomach. The lowest pH (6.2–6.4) in the rumen of animals in the experimental group was observed 1.5 h after feeding. At the same time the highest level of lactic acid was observed, but the highest level of volatile fatty acids (VFA) was observed 3 h after feeding. Although there was a large increase in ammonia in the rumen contents (approximately 20 mmol/l at 1.5 h after feeding) an increase in the blood level of ammonia was not observed.

3. A lower level of acetic acid and higher level of butyric acid and valeric acid were observed in the rumen of animals given sugar-beet silage than in animals given maize silage and ground barley. Non-glucogenic ratio of VFA in the rumen of bulls after feeding the experimental diet was approximately 3.5 while on the control diet the value was considerably higher.

4. The causes of the low concentration of glucose in the blood and changes in other metabolites in the blood of experimental animals are discussed.

5. Average daily gains were higher (P ≤ 0.05) in both groups of bulls given a diet containing sugar-beet silage and NPN (1087 and 1043 g/d) than with the control diet (887 g/d). Changes in the concentration of metabolites in the rumen contents and blood of sugar-beet-silage-fed bulls confirmed the possibility of effective addition of urea in an amount corresponding to 50% of the N content and also indicated good utilization of the energy in this diet.

The decreased folate uptake induced by exposure of rats to nitrous oxide can be partly reversed by methionine supplementation. This is consistent with the theory that N2O inhibits methylcobalamindependent methionine synthetase (EC 2.1.1.13) in rat liver and previous observations showing decreased folate incorporation in rats made nutritionally vitamin B12 deficient.

Using a well-known equation relating the heat production to the respiratory measurements, the total heat produced in the animal is partitioned into heat produced in the rumen and heat produced in the body. It is shown that the values of the partition constants can be calculated by making two simple logical deductions. Consideration of known heats of fermentation of carbohydrate and protein shows that the deductions are justified.