1. Immature male Wistar rats were given a low-zinc semi-synthetic diet (2 mg Zn/kg) for 28 d. Control groups received a similar diet supplemented with 58 mg Zn/kg either ad lib. or in amounts matched to the consumption of the Zn-deficient group. Rates of growth, food consumption and small intestinal length were significantly reduced in the Zn-depleted rats.

2. Zn deficiency in the rat was associated with a reduction in the ratio, crypt:villus and a lower rate of crypt cell division in the jejunum. This resulted in a substantial decrease in the net influx of new cells into the villi of the Zn-deficient animals compared with controls.

3. The fractional rates of protein synthesis in jejunal mucosa were measured by a technique based on the determination of L-[4-3H]phenylalanine incorporation. There was no evidence of a decline in the protein synthetic rate in total mucosa from Zn-deficient rats.

4. It is suggested that a reduction in cell influx into the villi may be responsible for the morphological and functional changes observed in the small intestine of rats fed on a low-Zn diet.

1. Pigs (n 100) between 28 and 56 d of age were given diets containing one of five protein concentrates ad lib.

2. The utilization of methionine from the protein concentrates was compared with synthetic methionine.

3. Increasing the methionine content of the diets from 1.5 to 2.2 g/kg diet increased the weight gains of the pigs from 61 g/d to 198–292 g/d. The feed conversion efficiencies decreased from 2.56 to 1.34– 1.56.

4. The utilization of methionine from the protein concentrates for weight gain, as compared with synthetic methionine, was meat meal A 0.89, meat meal B 0.97, soya-bean meal 1.02, cotton-seed meal 0.87 and dried skim milk 1.04.

1. 14C and 15N isotopes of urea were infused intravenously into rabbits for 6–8 h in order to measure urea synthesis and the extent of degradation in the digestive tract. The results indicate that 0.62 of the urea flux was excreted in the urine and that re-incorporation of urea-N following hydrolysis in the gut represented 0.3 of the urea synthesis rate.

2. Sampling of metabolites from the caecum by dialysis provided an opportunity to assess the contribution of urea-N to the caecal ammonia pool. This contribution is calculated to be 0.25 of caecal ammonia turnover.

3. Infusion of a urease (EC 3. 5. 1. 5) inhibitor during a continuous infusion of [14C]urea into the caecum permitted the measurement of urea turnover within the caecum.

4. Results obtained for urea entry into the caecum are contrasted with the measured urea degradation rate in the gut.

1. Following the addition of I4C-labelled casein to mixed rumen bacteria at 39°, some radioactivity was adsorbed to the bacteria before the casein was hydrolysed. At O°, the rate of hydrolysis was greatly diminished but adsorption still occurred, and this enabled a study of the adsorption mechanism to be made.

2. The adsorption of 14C-labelled casein to rumen bacteria was a saturable process. The maximum binding capacity was about 10 μ I4C-labelled casein/mg bacterial protein.

3. The ability of bacteria to adsorb 14C-labelled casein was abolished when they had been boiled for 5 min. Boiling caused the release of material from the bacteria which rendered some undigested protein soluble in 50 g trichloroacetic acid/l.

4. Adsorbed 14C-labelled casein could be partly displaced by the addition of Triton XI00 or an excess of unlabelled casein, or by boiling, or by removal of capsular material by blending. Adsorbed 14C-labelled haemoglobin could similarly be displaced by an excess of cold casein.

5. When an excess of casein was added to bacteria to which glucose-6-phosphate dehydrogenase (EC I. I.I.49) and glucosephosphate isomerase (EC 5.3. I.9) had been adsorbed, little active enzyme was displaced.

6. The susceptibility of different 14C-labelled proteins to hydrolysis corresponded to their relative adsorption affinities.

7. The pattern of sensitivity to inhibitors of the adsorption mechanism was the same as that for the inhibition of the bacterial hydrolysis of 14C-labelled casein, and the synthetic substrates leucine p-nitroanilide and benzoyl arginine p-nitroanilide.

8. It was concluded that the adsorption site and the catalytic site for proteolysis by rumen bacteria are probably identical and so not likely to be subject to independent manipulation.

1. Oxygen consumption and Na+,K+-ATPase(EC 3.6.1.3)-dependent (ouabain-sensitive) and -independent respiration were measured for duodenal mucosa biopsies from 10-month-old sheep given two levels of digestible energy (DE) intake (7.6–7.7 and 14.8 MJ lucerne (Medicago sativa) pellets/d) and following 48 h of starvation.

2. The mucosal biopsies were determined to be structurally intact and free of adherent bacteria on histological and scanning-electron-microscope examinations.

3. The use of D-glucose as a substrate during incubations did not elevate (P > 0.05) the respiration indices of the biopsies over those measured during acetate incubations.

4. Glucose uptake did not (P > 0.05) influence the Na+,K+-ATPase-dependent respiration of the mucosal biopsies.

5. Na+,K+-ATPase-dependent respiration accounted for 50% of the total O2, consumption of the mucosal biopsies of sheep given the lower level of DE.

6. Total O2, consumption of the duodenalmucosa was not (P > 0.05) increased when sheep were given the higher level of DE but Na+,K+-ATPase-dependent respiration of the mucosa was elevated (P < 0.01) by 37% during this period.

7. When sheep were starved for 48 h, total O2, consumption of the mucosal biopsies was not (P > 0.05) affected, however, Na+,K+-ATPase-dependent respiration of the biopsies dropped (P < 0.01) by 45%.

8. Na+,K+-ATPase-dependknt respiration accounted for 61.3% of the O2, uptakes of mucosa from the sheep given the higher level of DE and 28.3% of the 02, uptake of mucosa from fasted sheep.

1. Forty pigs between 23 and 51 d of age were given, ad lib., diets containing 7.9 g lysine/kg. The diets contained wheat and one of five protein concentrates: milk, peanut (Arachis hypogaea) meal, cotton-seed (Gossypium herbaceum) meal, meat meal or lupins (Lupinus augustifolius).

2. Twenty of the pigs were given an indigestible marker, 103Ru-labelled Tris-(1, 10-phenanthro1ine)-rthenium(II) chloride, between 51 and 56 d of age and were killed at 56 d of age.

3. A further forty pigs, between 23 and 51 d of age, were given the same diets supplemented with 3 g L-lysine hydrochloride/kg.

4. The weight gains of the pigs given the diets containing 7.9 g lysine/kg (95–153 g/d) were significantly less (P < 0.05) than those of the pigs given the diets containing 10.9 g lysine/kg (274–340 g/d).

5. Weight gains of pigs given the diets containing meat meal were less than those of pigs given diets containing milk, peanut meal or lupins.

6. Feed conversion ratios decreased and N balances increased with increasing lysine content of the diets.

7. Apparent digestibilities of dry matter (DM) and nitrogen of the diets containing meat meal and cotton-seed meal were less than those of the other three diets, but there was no effect of lysine content of the diets on these indices.

8. The major site of DM and N absorption for the diet containing milk was the duodenum while for the other four protein concentrates the jejunum and ileum were the major absorption sites.

9. Apparent digestibility of lysine from the five diets ranged from 0.54 to 0.75. The retention of the apparently absorbed lysine in weight gain was 0.8–0.94, and there was no significant (P > 0.05) difference between diets which suggested that the apparent digestibility of lysine could be an indicator of its availability.

1. Uterine, umbilical and, by difference, uteroplacental net uptakes of oxygen, glucose, lactate and 3-hydroxybutyrate (uterine uptake only) were measured in single-pregnant ewes which were either well-fed throughout, or severely undernourished for 8–20 d during late pregnancy. All animals were studied while standing at rest and then while walking on a treadmill at 0.7 m/s on a 10° slope for 60 min.

2. Undernutrition did not significantly affect fetal or placental weights at 143 d gestation but caused a 14% decrease in maternal live weight. Uterine blood flow was decreased by 32% and was associated with a significant decrease in uteroplacental oxygen uptake; neither umbilical blood flow nor fetal O2, uptake were affected by maternal plane of nutrition. Maternal and fetal hypoglycaemia in underfed ewes was accompanied by 46–63 % decreases in uterine, umbilical and uteroplacental net uptakes of glucose, and similar declines in uterine and umbilical glucose/O, quotients. Moderate maternal hyperketonaemia was associated with 2.5-fold and 3-fold increases in uterine net uptake of 3-hydroxybutyrate and 3-hydroxybutyrate/O2 quotient respectively.

3. Exercise caused significant decreases in uterine blood flow in fed and underfed ewes but did not affect uterine or umbilical O2 uptakes; uterine net glucose uptake increased in most ewes but umbilical uptake was not significantly affected. Umbilical net uptake of lactate was significantly reduced. In underfed ewes, the extent of hyperketonaemia was significantly reduced by exercise.

4. Contrary to earlier proposals, the ovine pregnant uterus is sensitive and adaptable to long- and short-term alterations in maternal energy balance, as achieved by chronic undernutrition and exercise respectively. Thus, the fetus and placenta significantly add to, but do not necessarily have priority over the energy demands of other tissues of the ewe.

1. Six Hereford and six Brahman steers were fed ad lib. Pangola grass (Digztaria decumbens) and Spear grass (Heteropogon contortus) hay alone and supplemented with rumen-degradable nitrogen and sulphur and minerals. The rumen digestion of the two feeds was determined by reference to the disappearance of substrate from nylon bags suspended in the rumen and withdrawn after intervals ranging from 8 to 120 h.

2. The digestion of the unsupplemented Pangola grass diet occurred more rapidly in Brahmans than in Herefords and was associated with higher rumen ammonia concentrations in Brahmans (40 v. 16 mg/l). The rumen NH3, concentrations were increased to over 100 mg/l by supplementation. The digestion rate increased in both breeds after supplementation and the breed difference disappeared. Increases in digestion rate were not achieved above NH3, concentrations of 60–80 mg/l.

3. Spear grass, especially the cell-wall-constituent fraction, was more resistant to digestion than Pangola grass. Digestion of the unsupplemented Spear grass diet proceeded more rapidly in Brahmans than in Herefords. The digestion rate in Brahmans were similar irrespective of whether the diet was supplemented or not. Supplementation increased digestion rate in Herefords.

1. In a number of experiments voluntary food intake of three low-quality roughages, either alone or supplemented with rumen-degradable nitrogen and sulphur and minerals, was measured in Brahman (Bos indicus) and Hereford (Bos taurus) steers. The chaffed hays were Spear grass (Heteropogon conform) (6.2 g N/kg organic matter (OM)), Pangola grass (Digitaria decumbens) (7.9 g N/kg OM), and Pangola grass (12.0 g N/kg OM). Rumen characteristics relating to rate of fluid outflow from the rumen were also determined.

2. There was no significant difference between breeds in the dry-matter intakes of the unsupplemented diets which ranged from 11.3 to 17.8 g/kg body-weight (BW) by Herefords and from 11.8 to 16.1 g/kg BW by Brahmans.

3. Supplementation of Spear grass with N and S significantly (P < 0.05) increased intake by Herefords (24%) but not by Brahmans. When the lower-N Pangola grass was supplemented there was a significant increase in intake by both breeds with the magnitude of the response in Herefords (42%) (P < 0.001) being greater than that in Brahmans (15%) (P < 0.05). The intakes of both the supplemented Spear grass and the lower-N Pangola diets were significantly (P < 0.05) greater by Herefords than Brahmans. There was no breed difference in intake when the higher-N Pangola grass was supplemented. Both breeds recorded an 8% intake response to supplementation, although the increase was only significant (P < 0.05) in Herefords.

4. The mean retention time of fluid in the rumen on the unsupplemented Pangola grass diet of lower N content was 12.7 h in Brahmans compared with 17.5 h in Herefords (P < 0.01). When the higher-N Pangola was fed, both alone and supplemented, the mean retention times were similar on both diets (10.5 and 9.9 h for Herefords; 9.5 and 8.1 h for Brahmans for unsupplemented and supplemented diets respectively).

5. Plasma urea concentrations were higher in Brahmans than in Herefords on all diets. Rumen ammonia concentrations were significantly (P < 0.001) higher in Brahmans than Herefords when the lower-N Pangola grass diet was unsupplemented.

6. The intakes and the variable intake responses to supplementation between breeds and diets are discussed in relation to a number of animal and dietary factors.

1. The effect of methylcobalamin inactivation by the gas nitrous oxide on plasma amino acid and tissue methionine levels in fruit bats (Rousettus aegyptiacus) was examined.

2. Animals exposed to N2O-oxygen (1:1, v/v) for 90 min daily received a fruit diet with or without methionine or betaine supplements. Exposure and diets were continued for up to 17 weeks or until neurological impairment and muscular weakness was established.

3. All the groups exposed to N2O had significantly lower liver, brain and plasma methionine concentrations except the methionine-supplemented animals which showed significantly raised levels. Plasma homocysteine, which was absent in controls, was present in all the N2O-exposed groups.

4. Betaine supplementation resulted in reduced accumulation of homocysteine in plasma. However, plasma and liver methionine levels were only slightly increased compared with animals on the basal diet, and brain methionine levels were the lowest of all the groups studied.

5. These results support the hypothesis that reduced methionine synthesis is an important contributor to the development of neurological impairment in this species and suggest that dietary supplementation with the methionine precursor betaine cannot replace the loss of vitamin B12-dependent methionine synthesis.

1. A multicornpartmental model, which assumes first-order kinetics, is proposed to describe digesta flow along the gastrointestinal tract of ruminants.

2. Solution of the model yields a multiplicative equation, containing a single-exponential term and a double-exponential term, for describing faecal outflow rate.

3. The logarithmic transformation of the equation was fitted to eighty-two excretion curves obtained after the administration of marker into the rumen of cattle and sheep, and compared with other published models.

4. It was found to be superior to the other models in that it fitted all the data sets successfully.

1. Two experiments of Latin square design, with four Friesian bull calves fitted with re-entrant duodenal cannulas at 4–10 d of age, were made to study the effect of giving varying levels of single-cell protein on the abomasal outflow and composition of digesta.

2. In Expt 1, diets in which 0,220,440, and 660 g/kg milk protein were replaced by the bacterial protein Pruteen were compared from 14 d of age. In Expt 2, which began at about 61 d of age, a comparison was made of diets in which 0, 220, 440 and 660 g/kg milk protein were replaced by the yeast protein Toprina.

3. Collection of abomasal outflow was made for 8 h after feeding for 2 d within each 6 d period of the Latin square design experiment. The amount of diet offered daily was 50 g dry matter/kg body-weight0.75. Polyethylene glycol (PEG), which was used as an indigestible marker, total nitrogen (TN), protein-N (PN), fat, and potassium, sodium and chloride ion outflows were measured together with pepsin (EC 3.4.23.1) and chymosin (EC 3.4.23.4) activities, pH and titratable acidity.

4. In Expt 1 there was little difference in the outflow of liquid digesta between diets and about 0.9 of the dietary PEG was recovered within the 8 h collection period. With increasing amounts of Pruteen in the diet, outflows of TN, PN, fat and Na+ increased, and the pH of digesta increased. However, the volume of 'apparent secretion' into the abomasum (outflow - intake), pepsin activity, chymosin activity, titratable acidity, (outflow of C1--outflow of Na+) as a measure of outflow of HC1, and outflows of K+ and of C1- were reduced. All outflows decreased with the time interval after feeding, except (Cl--Na+) outflow.

5. In Expt 2, the same trends as in Expt 1 were apparent, but since one calf had to be slaughtered and the experiment had to be analysed as a randomized block, only PN and K+ outflows and pH were significantly affected by dietary treatment, with K+ outflow increasing, rather than decreasing, with increasing concentration of single- cell protein in the diet.

6. Reduced proteolysis in the abomasum, associated with a faster and greater outflow of protein as a result of poor or no coagulation of protein in the abomasum, and a reduction in secretion of enzymes and in acidity may partly explain the poor protein digestibility and growth rate obtained in other experiments when diets containing more than 100 g single-cell protein/kg diet (about 200 g protein/kg total protein) were given to young calves.

1. In a 4 × 4 Latin square experiment four cattle were given in two meals per d diets consisting of (g/kg dry matter (DM)) 500 barley, 400 grass silage and 100 soya-bean meal. The diets were given at either 1.15 (L) or 2.3 times (H) maintenance energy requirements and the soya-bean meal was either untreated (U) or formaldehydetreated (T).

2. A 24 h collection of duodenal digesta and a 7 d collection of faeces were made using chromium sesquioxide for flow estimation and 35S as a marker of microbial nitrogen entering the small intestine. Samples of rumen fluid were also taken for estimation of lumen pH, ammonia and volatile fatty acid concentrations.

3. Spot samples of duodenal digesta were obtained after administration of Cr2O3,-mordanted silage-fibre and soya-bean meal, to determine the rates of outflow of these markers from the rumen. Similar samples were also obtained after cessation of a continuous intraruminal infusion of ruthenium phenanthroline, 35S and CoEDTA.

4. Incubations of each feedingstuff in porous synthetic fibre (psf) bags were carried out in the rumen and the rates of N disappearance from the bags determined.

5. Increasing DM intake significantly ( P < 0.001) increased the quantities of organic matter (OM), total N and amino acid-N entering the small intestine and amounts subsequently voided in the faeces. Apparent digestibilities of OM and N were unaffected by DM intake; the proportions of total digestible OM digested in the rumen were significantly lower (P < 0.01) at the higher level of DM intake.

6. Formaldehyde treatment of the soya-bean meal increased the quantities of N entering the small intestine; these increases were not significant.

7. Increased DM intake increased the quantities of both microbial N (P < 0.001) and undegraded feed N (P < 0.01) entering the small intestine; HCHO-treatment also significantly (P < 0.05) increased the quantities of undegraded feed N entering the small intestine. The efficiency of microbial N synthesis within the lumen was not significantly affected by dietary treatments whereas apparent feed N degradability was reduced significantly ( P < 0.05) both by increasing DM intake and by HCHO-treatment of the soya-bean meal.

8. Rates of disappearance of N from psf bags in the rumen were different for different feedingstuffs. However, for a given feedingstuff, the rate of N disappearance was not affected by the diets fed.

9. The rates of decline in marker concentrations measured in duodenal digesta were significantly increased as DM intake increased with the exception of Cr2O2-soya-bean meal. The markers could be ranked (P < 0.05) in the following order of increasing outflow rate: ruthenium phenanthroline, 35S-labelled amino acids and Cr2O2-silage fibre < Cr2O3-soya-bean meal < CoEDTA.

10. Estimates of the degradabilities of feedingstuffs were calculated from N disappearance rates from psf bags and either experimentally determined outflow rates or those proposed by the Agricultural Research Council (1984). Such estimates for the degradability of the whole diet were then compared with those determined in vivo using 35S as a marker.