1. Rat pups were artificially reared (AR) from post-natal day 5 by intermittent gastric infusion. Mother-reared (MR) siblings served as controls. Fourteen measures of body and organ growth were taken at the end of each experiment.

2. In Expt 1, two batches of pups were given rats' milk only, obtained by manual expression from anaesthetized dams.

3. The first batch, reared to 12 d, grew less well than the MR group, probably because they received too little milk. However, relative to body-weight, organ weights were as great or greater than those of MR pups, except for heart weight. The second batch, given more milk and reared to 20 d, showed no deficits in organ or body-weights, but excesses in kidney, gastrocnemius muscle, stomach and caecum weights. There were no losses from ‘bloat’, a condition of gastrointestinal distention often encountered in artificial rearing with milk substitutes.

4. Obtaining rats' milk is extremely labour-intensive and in Expt 2, more economical regimens were devised in which pups were started off on expressed rats' milk and then changed to a milk substitute resembling rats' milk in composition, either abruptly at 12 d or gradually between 8 and 17 d.

5. Both regimens were successful, in that there were no losses from bloat and most measures of growth were at least as great as in the MR group. Only heart weight was lower in both AR groups and adrenal weight in the abruptly changed AR group. The weights of the stomach and caecum and the length of the small intestine were all high in both AR groups.

6. It is concluded that giving rat pups expressed rats' milk for the first few days of artificial rearing largely avoids the problem of bloat and results in satisfactory growth.

1. A competitive protein-binding assay for 25-hydroxy vitamin D (25-OHD) in saliva has been established by adaptation of that previously described for 25-OHD in serum (Fairney et al. 1979).

2. Random values of salivary 25-OHD in patients attending hospital for venesection showed a wide range of results (105–1000 pg/ml, n 55). These values corresponded to 1.2% of the total serum values with which they showed a significant relation (r 0.45, P < 0.001).

3. There was no relation between salivary 25-OHD and measured serum free 25-OHD in eighteen pairs of saliva and serum studied.

4. Studies in two individuals showed that salivary 25-OHD values varied throughout the day and that a vitamin D load (19.5 μg), given as pickled herrings at lunch, produced a marked rise in 25-OHD values 5–8 h later.

5. Diurnal profile studies of salivary 25-OHD in Caucasian and Asian 11-year-old male schoolchildren showed lower values in Asian children eating a vegetarian diet, and a significant variation with time and ethnic group(P < 0.001).

6. It is concluded that 25-OHD is present in saliva and that the values vary throughout the day. The values obtained may relate to dietary intake of vitamin D and the subject's ethnic origin.

1. To characterize further the effect of protein-mineral interaction on plasma cholesterol, four groups of rabbits were placed on cholesterol-free, semi-purified diets for 12 weeks. The diets were similar in proximate composition with either casein or soya-bean protein isolate as the protein source (250 g/kg).

2. The dietary zinc content of the casein diets was increased to 22 mg/kg to equal that of the soya-bean diets. The copper content was set at 2 and 6 mg/kg. There were no differences in weight gain; all animals grew at a similar rate.

3. When the dietary Zn content was equalized, the plasma and liver cholesterol responses were similar regardless of the source of protein.

4. Differences in liver Cu and Zn were observed. As dietary Cu increased, Cu decreased and Zn increased in the liver. Hepatic Zn was also higher in soya-bean-fed than in casein-fed animals.

5. No effects on plasma Cu and Zn were seen.

6. The addition of Zn to the casein diet resulted in a similar plasma cholesterol to that of animals fed on the soya-bean diet, suggesting that casein-induced hypercholesterolaemia is due to a marginal Zn intake.

1. Weanling male rats were maintained on diets containing 5, 10, 20, 40, 80 or 160 mg zinc/kg for 14 d. On day 15 they received 65Zn either by intraperitoneal injection or in a test meal containing 20 mg Zn/kg. After dosing, the rats were again maintained on the diets they had received previously.

2. Whole-body 65Zn retention was measured immediately after dosing and daily for a further 9 d. From regression analysis of the semi-logarithmic plots of 65Zn retention from 0 to 192 h after 65Zn administration, the true extent of 65Zn absorption and the biological half-life (t1/2) of body 65Zn stores were calculated.

3. At the end of the experiment, the rats were killed and the entire small intestines of some rats from each group were rapidly flushed out to remove food and faecal residues, frozen in liquid nitrogen and stored under an atmosphere of N2 at –20° before separation of cytosolic Zn-binding fractions by gel filtration on Sephadex G–75.

4. The results suggest that rats which received diets that were either deficient(5 mg Zn/kg), marginal (10 mg Zn/kg) or adequate (20–80 mg Zn/kg) in Zn achieved homeostatic regulation of body Zn by changes in both the extent of Zn absorption and excretion. However, when Zn supply was excessive, increasing from 80 to 160 mg Zn/kg, no further changes were seen in Zn absorption, and homeostatic control appeared to be effected entirely by changes in rates of body Zn loss.

5. Gel chromatography of intestinal cytosol on Sephadex G-75 revealed that Zn was associated with two major fractions. The first (peak 1) had a molecular weight (MW) > 75 kdaltons and the second (peak 2), a MW of approximately 10 kdaltons and was assumed to be metallothionein.

6. There was no obvious relation between the amount of Zn bound to peak 1 and dietary Zn content. In contrast, the amount of Zn recovered in peak 2 increased linearly with increasing dietary Zn content.

7. Comparisons between the effect of dietary Zn content on Zn bound to peak 2 and 65Zn retention may, depending on the range of Zn intakes, indicate possible roles for intestinal metallothionein in the control of Zn absorption or excretion.

8. A study of the effects of dietary dose of 65Zn on the extent of 65Zn absorption in rats of normal Zn status indicated a possible biphasic relation. At low doses (5–40 mg Zn/kg) 65Zn absorption appeared to exhibit a curvilinear response to increasing 65Zn dose, indicating possibly a saturable process. At higher doses (40–160 mg Zn/kg) the capacity of this process appeared to be exceeded and 65Zn absorption increased in a linear fashion.

1. Brush-border-membrane vesicles were prepared from piglet small intestines and the uptake of 65Zn was studied using a rapid filtration assay. The mechanism of 65Zn uptake was complex and two processes were identified.

2. In the first process, 65Zn uptake was rapid, reached equilibrium in 5–15 min and had an optimum pH of 7.5. The uptake was saturable and involved both binding to, and transport across, the membrane. The initial phase of 65Zn uptake (1 min incubation) approached saturation at high levels of substrate 65Zn and a Michaelis-Menten constant (Km) of 67.0 µM was calculated. Maximum uptake at equilibrium was approximately 100 nmol/mg protein. Cupric, ferrous and ferric ions had no effect on the uptake, but cadmium ions inhibited it competitively. The results are consistent with a carrier-mediated process, possibly involving a protein receptor in the membrane which is specific for Zn and elements close to it in the periodic table. Lactoferrin stimulated 65Zn uptake by approximately 20% when pre-incubated with 65Zn at a concentration of 0.01 µg/ml. It had no significant effect on 65Zn uptake at higher concentrations or when pre-incubated with brush-border-membrane vesicles.

3. The second mechanism of 65Zn uptake was linear with respect to time and involved binding to the membrane only. It was inhibited by all divalent and trivalent metal ions tested and is probably a passive binding process.

4. The results are discussed with respect to the use of brush-border-membrane vesicles in examining the role of nutrient interactions and their effect on the biological availability of nutrients.

1. Pure swards of perennial ryegrass (Lolium perenne cv. Melle) and white clover (Trifolium repens cv. Blanca) were harvested daily as primary growth (grass in May, clover in June) or regrowths (clover only in July) and offered, in the long form, to growing cattle at a feeding rate of 22 g dry matter/kg live weight. With each forage, two treatments were compared with the untreated forage (C): monensin (100 g active ingredient/kg, 250 mg/d) addition to the rumen (treatment M) or formaldehyde (30 g/kg crude protein (nitrogen x 6.25)) application to the diet (treatment F). The objective of the experiment was to examine means of manipulating N metabolism in the rumen and the duodenal non-ammonia-N (NAN) supply derived from fresh forages.

2. The apparent digestion of ingested organic matter (g/kg) in the rumen was unaffected by treatment M (C 509, M 497) but was significantly (P < 0.01) reduced by treatment F (443). The extent of cellulose digestion in the rumen was not affected by any of the treatments imposed and the changes in organic matter digestion were due mainly to effects on N digestion and rumen microbial synthesis. On the untreated diets, duodenal NAN supply averaged 0.74 g/g N intake and treatment M caused a small but non-significant increase (M 0.79 g/g N intake). In contrast, the effect of treatment F was much larger (F 0.91 g/g N intake; P < 0.01). These differences were accompanied by corresponding reductions in rumen NH3 concentrations (mg/l; C 350, M 310, F 220; P < 0.001).

3. Of the increased flow of NAN to the small intestine observed on the white clover only diets with treatment F, 0.70 was accounted for by an increased net synthesis of microbial N, while treatment M had no effect on microbial N synthesis and a marginal reduction in feed N degradability only with the regrowth white clover diet. Treatment F reduced feed N degradability to a limited extent on both clover diets (C 0.82, M 0.81, F 0.77). No corresponding measurements were made for the ryegrass diets.

4. It is concluded that the extensive loss of N from the reticulo-rumen of cattle fed on fresh forages can be reduced by the use of agents to reduce protein solubility. However, the study demonstrated that treatment F may in some circumstances increase N supply to the small intestine more through enhancing microbial N synthesis within the rumen than through increasing the passage of undegraded feed N to the small intestine. The use of monensin, to manipulate proteolytic or deaminative activity in the rumen, or both, was not found to confer any beneficial effects on duodenal-NAN supply.

1. Adult male rats were fed on diets containing 100 g dietary fibre/kg either as α-cellulose or wheat bran or the pericarp-seed coat or aleurone layers prepared from that bran by sequential milling and air elutriation and electrostatic separation.

2. After 10 d, concentrations of total volatile fatty acids (VFA) in caecal fluid were significantly different between groups and fell in the order: aleurone > wheat bran > pericarp-seed coat > cellulose. This ranking probably reflected the ease of fermentation of fibre polysaccharides by colonic bacteria which also resulted in a considerably higher faecal bacterial mass in the aleurone group.

3. Because of the differences in the volume of caecal digesta, the mass of caecal VFA was considerably the highest in the aleurone group, intermediate with wheat bran and equally low in the pericarp-seed coat and cellulose groups.

4. The diet based on aleurone gave a relatively higher proportion of propionate but with both pericarp-seed coat and wheat bran the contribution of butyrate was raised.

5. VFA concentrations in hepatic portal venous plasma were proportional to caecal concentrations with very high (> 3 mM) values being recorded in the aleurone group.

6. The findings are discussed in relation to the apparent susceptibility of the morphological components of wheat bran to fermentation by large bowel bacteria.

1. Wether lambs of 29–44 kg live-weight, totally nourished by the infusion of volatile fatty acids (VFA) into the rumen and casein into the abomasum, were given five treatments in consecutive periods. The treatments were (daily amounts per kg live weight (W)0.75): (a) high-protein for 7 d (2500 mg nitrogen, 650 kJ VFA); (b) low-protein for 7–15 d (525 mg N, 650 kJ VFA); (c) N-free for 7 d (no N, 450 kJ VFA); (d) very-low-protein for 24–28 d (300 mg N, 400 kJ VFA); (e) high-protein for 40 d (2500 mg N, 650 kJ VFA). Nine lambs were subjected to treatments (a), (b) and (c) (Expt 1) and four of the lambs additionally received treatments (d) and (e) (Expt 2).

2. In Expt 1 all nine lambs had a positive N retention on treatment (a) but abrupt change to treatment (b) resulted in substantial negative N balances initially, and a period of approximately 5 d adaptation was required before N equilibrium was re-established. Animals again exhibited negative N balances when the N-free infusion (treatment c) was introduced and during that period there was no evidence of adaptation. Basal urinary N excretion was estimated to be 356 (SE 12) mg N/kg W0.75.

3. In Expt 2 all four lambs were depleted of N when receiving the very-low-protein treatment (d). The progressively decreasing N losses recorded during days 1 to 12 of the treatment period were slightly greater than those recorded during days 13 to 28 but the difference between the means was not significant (P > 0.05). There was no evidence of an adaptation in N retention between days 13 and 28 of the treatment. As assessed during days 13 to 28 of the treatment the efficiency of utilization of infused casein N was 1.0; this compared with a value of 0.66 recorded during treatment (b) in Expt 1. Live weight loss during the period of N depletion was 101 (SE 27) g/d.

4. When lambs were given treatment (e) during the last period of Expt 2, N repletion was rapid and complete within a few days. Ten days after the introduction of the treatment the rate of N retention was estimated to be 1019 (SE 38) mg/kg W0.75 per d and this value declined at a rate of 9.5 (SE 1.9) mg N/kg W0.76 per d for the following 30 d. In comparison, N retention determined for the high-protein treatment in Expt 1 was 724 (SE 66) mg N/kg W0.75 per d. Live-weight gains during N repletion were 292 (SE 26) g/d.

5. It is concluded that N-depleted lambs can replete rapidly and that enhanced N accretion (compensatory growth) may persist for 4–5 weeks. If the improved efficiency of utilization of infused N observed during N depletion reflects a changed basal N requirement, the validity of simple factorial systems for estimating N requirement is called into question.

1. In an incomplete 5 x 5 Latin square experiment, four cattle were given grass silage in two meals per d to satisfy 1.15 maintenance energy requirements. In addition, water or casein (21 g nitrogen and 0.17 kg organic matter (OM)/d) or urea (U; 28 g N/d) or a glucose syrup (G; 0.87 kg OM/d) or casein and glucose syrup (CG; 17 g N and 0.93 kg OM/d) were infused intraruminally at a constant rate.

2. A 24 h collection of duodenal digesta was made using chromic oxide for flow estimation and 35S as a marker of microbial N entering the small intestine. Samples of rumen fluid were also taken for estimation of rumen pH, and concentrations of ammonia-N and volatile fatty acids.

3. The intraruminal infusions had no significant effects on rumen pH, concentrations of volatile fatty acids or their molar proportions. Infusion of either C or U significantly (P < 0.05) increased rumen NH3-N concentrations whereas infusions of either G or CG lowered rumen NH3-N concentrations.

4. Infusions of C or U had no significant effect on the quantities of OM, acid-detergent fibre (ADF) or N constituents which entered the small intestine.

5. Infusions of G or CG increased the quantities of OM (G P < 0.05, CG P < 0.01), ADF (CG P < 0.05), non-NH3-N (G P < 0.05, CG P < 0.01), amino acid N (G P < 0.05, CG P < 0.01) and microbial N (G P < 0.05, CG P < 0.01) which entered the small intestine.

6. The efficiency of rumen microbial N synthesis was unchanged by the infusion of C, U or G (P > 0.05) but increased significantly (P < 0.05) when CG were infused.

1. The effects of Revalor (trenbolone acetate plus oestradiol) implantation or the inclusion of clenbuterol (a β-2-adrenergic agonist) in the diet of wether lambs was studied. Using continuous intravenous infusion of [3H]tyrosine the fractional synthetic rate of mixed protein from three separate muscles was measured.

2. Clenbuterol slightly increased growth rate but had a significant (P < 0.02) effect on food conversion efficiency. The weight and protein content of the longissimus dorsi and vastus lateralis muscles were increased but no such changes were observed for the vastus intermedius. For the longissirnus dorsi at least the increase was probably achieved by a reduction in fractional degradation rate of the muscle protein.

3. Revalor significantly increased the growth rate and food conversion efficiency of the animals. This increase was not specific for muscle. Estimated degradation rates of muscle protein were lower in the treated animals.

4. The possible mode of action of these materials was discussed. The results obtained again highlight the importance of protein degradation in controlling growth.

1. The objective of the present study was to evaluate effects of in vitro rumen solubility or degradability of dietary protein on net absorption of nitrogenous compounds from portal-drained viscera of beef heifers.

2. Four protein sources, casein, soya-bean meal, maize-gluten meal and blood meal provided about two-thirds of total dietary nitrogen in semi-purified diets given to four beef heifers in a 4 x 4 Latin square design.

3. Although in vitro degradability of dietary N ranged from 842 (casein) to 310 (blood meal) g/kg total dietary N, net absorption of ammonia-N or α-amino-N was not significantly different (P > 0.10) among diets. However, net absorption of NH3-N tended to decrease and net absorption of α-amino-N tended to increase as intake of in vitro undegradable N increased. Net transfer of urea-N from plasma to portal-drained viscera was greater (P < 0.10) when heifers were fed on soya-bean meal than when fed on maize-gluten meal or blood meal.

4. The findings show with all diets that the non-protein-nitrogenous compounds, NH3 and urea, played a substantial role in absorption and transfer of N. Overall, net absorption of NH3-N was 61% of net absorption of α-amino-N, and transfer of urea-N from plasma to portal-drained viscera was 80% ofnet absorption of α-amino-N.

1. Sheep were used to evaluate the nutritional consequences of a low condensed-tannin concentration (22 g/kg dry matter (DM)) in lotus (Lotus corniculatus L.) (control group) compared with lotus given to sheep receiving intraruminal polyethylene glycol (PEG) infusion (PEG group). PEG selectively binds to tannins and prevents tannins from binding proteins.

2. DM intakes (1430 (SE 28) g/d) and digestibility of energy (663 (SE 4.5) kJ/MJ intake) were similar for both groups but the apparent digestion of nitrogen was lower in the control sheep (0.70) than in the PEG sheep (0.78; P < 0.001).

3. The proportion of N apparently digested before the abomasum (i.e. in the rumen) was lower (P < 0.05) in control sheep (0.12) than in PEG sheep (0.21; P < 0.05). Rumen ammonia concentrations were lower (P < 0.001) in control sheep than in PEG sheep. The proportion of neutral-detergent fibre (NDF) digested in the rumen was similar for both groups (0.48 (SE 0.012)) but less energy was digested in the rumen of the control (0.42) than of the PEG sheep (0.47; P < 0.05).

4. The flux of essential amino acids (EAA) through the abomasum of control sheep was 50% greater than that in PEG sheep; flux of non-essential amino acids (NEAA) was 14% higher in control than in PEG sheep. Apparent digestibility of EAA in the small intestine was similar for both treatments (0.67), but NEAA were less well digested in the control (0.55) than in the PEG sheep (0.69).

5. The presence of tannins in the control group increased net apparent absorption of threonine (57%), valine (89%), isoleucine (94%), leucine (30%), tyrosine (41%), phenylalanine (93%), histidine (90%) and lysine (59%), and reduced NEAA absorption by 10%, compared with PEG sheep.

1. Four rumen-cannulated steers were given barley and maize diets supplemented with graded levels of an ammonium acetate solution.

2. Animals were fed hourly from automatic feeders and water consumption was controlled to achieve steady-state conditions in the rumen.

3. Dacron bags containing rolled barley or ground barley were incubated in the rumen of barley-fed steers, while ground maize and autoclaved maize were incubated in the rumen of maize-fed steers.

4. Fractional degradation rates of dry matter were estimated for each cereal substrate incubated using a single-pool exponential decay model.

5. No differences in degradation rate due to the method of feed processing were detected; however, barley was degraded at a faster rate than maize. Furthermore, the minimum rumen ammonia-nitrogen concentration required to maximize the degradation rate of barley (125 mg/l) was greater than that required to maximize the degradation rate of maize (61 mg/l).

6. These results indicate that the optimal NH3-N concentration required to maximize the rate of grain digestion in the rumen is influenced by the chemical or structural characteristics of the grain.

1. Measurements have been made of protein turnover, RNA and DNA in thymus and skeletal muscle from rats fed on a zinc-deficient diet (ZD) for 10 and 17 d, in pair-fed controls (CI) and in muscle from rats fed on the ZD diet for 24 d and then fed on restricted amounts of the deficient diet with (RIZS) or without (RIZD) Zn supplementation, for 8 d.

2. In thymus the ZD diet induced a loss of DNA and protein which was not observed with the CI rats. Accumulation of RNA was less affected but protein synthesis was reduced.

3. In muscle the accumulation of DNA and protein was slowed by the ZD diet, particularly in glycolytic muscles compared with oxidative muscles, and Zn supplementation increased DNA and protein.

4. Protein synthesis and RNA concentrations were reduced in the ZD rats compared with the CI rats, but Zn supplementation at constant restricted food intake did not increase protein synthesis. Muscle protein synthesis per unit RNA varied markedly in the ZD rats after 10 d when the characteristic cycling of the food intakes and body-weight was most pronounced, the highest values being observed in the anabolic phase of the cycle although these were less than values for well-fed controls. The variability was inversely correlated with the plasma Zn levels. The extent of the variability was much less after 17 d and was not apparent in the food-restricted ZD animals.

5. Protein degradation in muscle, assessed as the difference between overall and net protein synthesis, was faster in the ZD rats compared with the CI rats and fluctuated considerably, partly accounting for the cyclic changes in muscle after 10 d, and was entirely responsible after 17 d. The concentration of muscle-free 3-methylhistidine and its urinary excretion rate indicated inconsistent results which could not be satisfactorily interpreted.

6. Plasma insulin was reduced in the ZD rats compared with the CI rats and was insensitive to food intake in contrast to urinary corticosterone excretion which was inversely correlated with the cyclic changes in body-weight and food intake. Furthermore, adrenalectomized rats exhibited increased mortality and reduced cycling of body-weight and food intake.

7. Thus Zn deficiency impairs growth by a combination of (a) reduced food intake, (b) a reduced anabolic response to food due to a reduced capacity for protein synthesis and reduced activation of protein synthesis, possibly reflecting impaired insulin secretion, and (c) an increased catabolic response to the reduced intake in which corticosterone may play a role.