1. Metabolic balance studies (5 d) for nitrogen were carried out in twenty-four apparently healthy elderly people (age 69.7–85.6 years) and a heterogeneous group of twenty housebound elderly people (age 69.9–85.1 years) with chronic diseases. During the study all subjects ate self-selected diets, lived in their own homes and continued their normal daily activities. Seven of the housebound received meals-on-wheels 5 d/week.

2. Healthy men and women had mean metabolizable energy intakes of 8.7 and 6.6 MJ/d respectively compared with 6.3 and 4.8 MJ/d in the housebound. The average energy content of the meals-on-wheels as delivered was 2.4 MJ per meal, of which 2.1 MJ were consumed.

3. The healthy men and women had average daily protein intakes of 69.4 and 59.7 g respectively compared with 46.3 and 39.1 g in the housebound. Meals-on-wheels as supplied provided 19.4 g protein per meal, of which 16.2 g were consumed.

4. Healthy subjects were in equilibrium for N balance (0 mmol/d) with a daily intake of 733 mmol, which was equivalent to 11.04 mmol N (0.97 g mixed protein)/kg body-weight per d. Housebound individuals were in negative N balance (–95 mmol/d) with an intake of 475 mmol/d, corresponding to 7.59 mmol N (0.67 g mixed protein)/kg body-weight per d.

5. We were unable to determine in the present study whether the negative N balance observed in the housebound people was due to the relatively low N intake or the underlying disease condition.

1. Plant foods were digested in vitro and the proportion of iron which diffused across a ssemi-permeable membrane was used as an index of Fe availability.

2. The mean (with SEM) Fe diffusibility from a group of eighteen cereals, legumes and nuts was very low, 2.1 (0.25)%, whereas from a group of sixteen fruits and vegetables it was high, 13.7 (1.09)%. The difference between the two food groups was highly significant (P < 0.001).

3. The results for Fe diffusibility correlated well with literature values for the in vivo absorption of Fe from similar foods (r0.84, P < 0.01).

4. When phytate, citrate and ascorbate were added to selected foods in amounts corresponding to endogenous levels, only phytate and citrate gave the expected effects on Fe diffusibility. Ascorbate only enhanced Fe diffusibility to the expected extent when it was added in much larger amounts, not normally found in foods.

5. When added to cereal foods, orange juice was found to enhance greatly Fe diffusibility even when its content of ascorbate was completely destroyed by boiling followed by prolonged storage. When citrate and ascorbate were added to cereal foods in amounts equivalent to those found in fresh orange juice, both enhanced Fe diffusibility but citrate was far more effective.

6. It is concluded that phytate is a major inhibitor of Fe diffusibility in cereals, legumes and nuts. However, citrate rather than ascorbate would appear to be the major enhancer of Fe diffusibility from many fruits and vegetables.

7. The implications of the present results are discussed in relation to the relative influence of phytate, citrate and ascorbate on dietary Fe availability.

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. Total methane excretion (CH4 in breath+flatus) was measured in two experiments with thirty-six castrated male pigs (Danish Landrace) during the growth period from 20 to 120 kg live weight (LW). In Expt A, twenty-eight pigs were fed on a commercial diet alternately at high (HFL; metabolizable energy (ME) 1234 (SE 41) kJ/kg LW0.75) or low (LFL; ME 784 (SE 31) kJ/kg LW0.75) feed levels in different weight classes. In Expt B, eight pigs were constantly fed on a semi-purified diet at HFL without (-oil) or with 90 g soya-bean oil/kg diet (foil) corresponding to daily intakes of ME of 1339 (SE 11) and 1413 (SE 8) kJ/kg LW0.75 respectively.

2. CH4 excretion was measured during 24 h respiration trials in open-air-circulation chambers.

3. About 1 litre CH4 was excreted per day at 20–25 kg LW increasing to a maximum of 12 litres at 120 kg LW, which corresponded to no more than 1.2% of dietary gross energy.

4. In Expt A, CH4 excretion increased linearly with LW, while in Expt B the increase was linear until about 70 kg LW, when it reached a plateau. On average LFL reduced CH, excretion by 23% compared with HFL. When related to dry matter (DM) intake, however, the pigs on LFL excreted 3.1 litres CH4/kg dietary DM and those on HFL 2.5 litres CH4/kg dietary DM, the difference being significant (P < 0.05). In Expt B the inclusion of soya-bean oil in the basal diet (+oil) reduced CH, excretion by 26% compared with the diet without oil (-oil). The pigs receiving the basal diet excreted 5.2 litres CH4/kg DM and the pigs receiving soya-bean oil 4.3 litres CH4/kg DM, the difference being highly significant (P < 0.001). All differences between Expt A and B in CH4 excretion based on DM intake were highly significant (P < 0.001).

5. The results are discussed in relation to gas production in ruminants, rats and humans. It is suggested that flatus production may not only be reduced by changing the composition of the dietary carbohydrates, but also by inclusion of a polyunsaturated oil in the diet of simple-stomached animals and humans.

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. The digestible energy (DE) and metabolizable energy (ME) values of a commercial Polydextrose® product and the polymer that it contained were determined by metabolic energy balance in male Wistar rats and compared with values obtained by radiochemical balance using a radiochemical analogue. The energy values of the whole preparations and of the polymer fractions were estimated.

2. In the energy-balance study of 6 d duration, 100 g maize starch/kg control diet were replaced by Polydextrose® to provide a test diet. Polydextrose® had no significant effects on food intake, body-weight gain, digestibility of nitrogen and N retention but significantly increased the water consumption to 143% of the control value (P < 0.05) and the water content of fresh faecal pellets from 548 (SE 10) to 646 (SE 15) g/kg wet weight (P < 0.01).

3. By energy balance the DE in the Polydextrose® product and in the polymer that it contained were 13.5 and 12.8 (SE 1.9) kJ/g respectively. The corresponding ME values were 12.7 and 12.1 (SE 1.8) kJ/g respectively. These values were higher (P < 0.05) than the corresponding values obtained by the radiochemical balance procedure: DE 8.8 and 8.6 (SE 0.4) kJ/g polymer respectively and ME 8.0 and 7.8 (SE 0.5)kJ/g polymer respectively.

4. These findings indicate relatively high energy values for Polydextrose® by comparison with previously published values and illustrate a potential difficulty when using energy values obtained by certain radiochemical methods to estimate the energy values of a mixed diet given to rats. Several alternative explanations of the discrepancies are advanced.

1. Complete energy balance measurements were made in exercise-trained (treadmill running) rats subjected to 27 d of exercise detraining.

2. The 20% difference in body-weight that existed at the end of the training period between sedentary and trained rats was negated by detraining. Detrained rats had twice the body-weight gain of their untrained controls.

3. An elevation (12%) in metabolizable energy (ME) intake (relative to body-weight) was observed in detrained rats while their gross energetic efficiency was augmented by 60%.

4. Energy expenditure, excluding the estimated costs of fat and protein storage, was similar for detrained and untrained rats. Complementing the latter was the finding that thermogenesis in brown adipose tissue, a known energy buffering process, was also similar.

5. Elevated ME intake (relative to body-weight) largely contributed to the increased energetic efficiency of detrained rats.

1. The effect of prolonged consumption of guar gum on iron absorption and Fe status was investigated in rats. Experiments with closed loops of duodenum, isolated in siru, were designed to reveal changes in the short-term regulation of duodenal Fe uptake, induced by challenge with low- and high-Fe meals. In separate experiments, the effect of guar gum on the capacity of intact rats to maintain Fe status and to absorb Fe from a test-meal was investigated.

2. Male Wistar rats were given either a control, semi-synthetic diet (C) for 21 d or a similar diet containing 100 g guar gum (G)/kg for 27 d. Both diets contained 36 mg Fe/kg. Two subgroups were then challenged with meals containing low-Fe (8 mg/kg) or high-Fe (566 mg/kg), while a third subgroup received a meal of the control diet (36 mg Fe/kg). At intervals of 12, 36, 60 and 84 h after the dietary challenge, the uptake of [59Fe] ferric citrate was measured using closed duodenal loops in situ. All G-supplemented animals absorbed less Fe than their C-fed counterparts. Within group C, animals given the high-Fe challenge had lower absorptions 12, 36 and 60 h later, compared with those given the maintenance diet, whilst those given the low-Fe meal showed much increased uptake 12 and 36 h later. The latter effect was virtually abolished by guar gum.

3. In the second experiment, male Wistar rats were fed on the C or G diets containing 8, 15, 20, 26 or 36 mg Fe/kg for approximately 10 weeks ad lib. Fe retention from a starch-sucrose test meal extrinsically labelled with 59Fe was then measured, together with packed cell volume and Fe content of the liver as indices of Fe status. No effect of feeding guar gum on Fe retention nor Fe status at any level of Fe intake was observed.

4. It was concluded that feeding guar gum leads to a small reduction in the rate of uptake of Fe in the rat duodenum and to an impairment of the regulation of uptake in response to brief episodes of dietary Fe depletion. However, these changes do not apparently lead to any nutritionally significant reduction in the capacity of the intact animals to absorb Fe and maintain their Fe status.

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. Interrelations between bacterial metabolites (volatile fatty acids, lactate) in the gut contents and the blood in relation to the faecal excretory cycle (soft or hard faeces) were studied in anaesthetized rabbits.

2. It appeared that the level of organic acids in the alimentary tract varied cyclicly with the faecal excretion pattern. The lactate entering the portal circulation originates from the stomach, while the volatile fatty acids (VFA) originate from the hind-gut. Net absorption from the digestive tract and hepatic utilization of fermentation acids were greater when the rabbits produced hard faeces (hard-phase) compared with soft faeces (soft-phase). Propionate and butyrate reaching the liver were almost quantitatively removed; acetate and lactate were available for extra-hepatic tissue metabolism.

3. Whatever the excretion pattern the levels of VFA in the arterial circulation remained remarkably constant; blood lactate, however, was lower during the soft-phase.

4. Absorption of bacterial metabolites, like their metabolism in the liver, showed a circadian rhythm parallel to the changes in the activity of the adrenal glands, i.e. the activity was enhanced during the hard-phase.

1. It was demonstrated that the development of experimental avitaminosis A in chicks led to secondary zinc deficiency. The balance of Zn in the chick became negative, while the Zn content of various tissues decreased. Thus in vitamin-A-deficient chicks the serum Zn content was 1258 (SD 26.3) μg/l which was considerably lower than 1652 (SD 97.8) μg/l in controls.

2. Zn absorption was considerably reduced throughout the entire small intestine of vitamin-A-deficient chicks and most markedly in the ileal region. Within 72 h after retinyl acetate administration Zn absorption was fully restored in this region of the intestine.

3. The 65Zn-binding capacity of soluble proteins, present in the supernatant fraction of ileal-mucosa homogenates of vitamin-A-deficient chicks, was found to increase 2.6 times by 72 h after the administration of a single dose of retinyl acetate.

4. A vitamin-A-dependent Zn-binding protein (ZnBP), absent in vitamin-A-deficient chicks, was isolated from the ileal mucosa after their repletion with vitamin A. Competitive-binding studies (calcium, cadmium, copper) showed the protein to be highly specific for Zn ions.

5. The molecular weight of ZnBP wa5 83 kDa. The association constant of the protein-Zn complex was 0.8 x 106/mol. The protein was acidic with approximately 20% of its amino acid residues belonging to dicarboxylic acids. ZnBP was found to be a glycoprotein, and it contained hexose as a carbohydrate component.

6. It is suggested that ZnBP is involved in the binding of Zn in the ileal mucosa of chicks.

1. The oxidation rates of lauric, myristic, palmitic, stearic, oleic, α-linolenic, linoleic, γ-linolenic, dihomo- γ-linolenic and arachidonic acids were studied by use of a radioisotope tracer technique in weanling rats at rest in a metabolism chamber over 24 h.

2. Of the saturated fatty acids, lauric acid (12:O) was the most efficient energy substrate: the longer the chain length of the saturated fatty acids, the slower the rate of oxidation.

3. Oleic acid (18:1) was oxidized at a remarkably fast rate, similar to that of lauric acid.

4. Of the ω6 essential fatty acids studied, linoleic acid (18:2ω6) was oxidized at a faster rate than any of its metabolites, with arachidonic acid (20:4ω6) being oxidized at the slowest rate.

5. The rate of oxidation of γ-linolenic acid (18:3ω3) was almost as fast as that of lauric and oleic acids.

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.Six Friesian heifers (250 kg live weight) with permanent cannulas in the rumen and abomasum were allocated at random into two groups of three. One group was treated with Teric GN9 (ICI (Aust.) Ltd) to defaunate the animals during the first two of the four periods of the experiment, after which they were refaunated. The second group was treated with Teric at the end of the first two periods. The dietary treatments were: paspalum (Paspalum dilatatum) hay (4.1 kg/d) given alone and the hay supplemented with urea (20 g/kg dry matter).

2. Defaunation was not complete but the approximate volume of protozoa in the rumen of treated animals was less than 6% of that in the untreated animals.

3. The amount of organic matter (OM) digested in the stomach was lower (P < 0.01) in animals with reduced fauna than in those with normal fauna. There were reductions in both the apparent OM digestibility in the total tract (from 0.56 to 0.52, P < 0.01) and the proportion of the digestible OM digested in the rumen (from 0.82 to 0.79, not significant) of animals with reduced fauna. Apparent digestibilities of acid-detergent fibre and neutral-detergent fibre were significantly lower (P < 0.01) in animals with reduced fauna.

4. The amount of nitrogen disappearing from the stomach was significantly higher (P < 0.01) with the urea supplement; effects due to concentrations of protozoa were not significant. The flow of non-ammonia-N from the abomasum was higher (P < 0.05) in animals with reduced fauna than in animals with normal fauna. The flows of bacterial N from the abomasum and the efficiencies of bacterial N synthesis were not significantly affected by the treatments. N retention was higher (P < 0.01) in animals receiving the urea supplement but differences due to protozoa were not significant.

5. Protozoal contribution to the microbial N flowing from the rumen of animals with normal fauna was estimated to be 24 and 27% with and without the urea supplement respectively.

6. Concentrations of rumen-fluid ammonia-N were reduced (P < 0.05) and those of volatile fatty acids were increased (P < 0.01) with reduction in protozoal numbers. Molar proportions of propionic acid increased (P < 0.05) and of butyric acid decreased (P < 0.01) with reduced rumen fauna.

7. Rumen water volume was lower (P < 0.05) and the mean retention time of indigestible acid-detergent lignin tended to be higher in animals with reduced fauna. Rumen dry-matter pool and mean retention time of CrEDTA were not significantly different between treatments.

1. The effect of starvation on whole-body protein synthesis and on the contribution of protein synthesis to basal metabolic rate was investigated in young chickens (Expt 1). Strain differences between layer and broiler chickens in whole-body protein synthesis and degradation rates were examined when the birds were starved (Expt 2).

2. In Expt 1, 15-d-old White Leghorn male chickens were used, while in Expt 2 Hubbard (broiler) and White Leghorn (layer) male chickens at 14 d of age were used. They were starved for 4 d, and heat production was determined by carcass analysis after 2 and 4 d of starvation. Whole-body protein synthesis rates were measured on 0, 2 and 4 d of starvation (Expt 1), and on 0 and 4 d of starvation (Expt 2).

3. The results showed that starving reduced whole-body protein synthesis in terms of fractional synthesis rate and the amount synthesized. Whole-body protein degradation was increased by starvation both in terms of fractional synthesis rate and the amount degraded on a per kg body-weight basis.

4. Reduced fractional synthesis rate of protein in the whole body was accounted for by reductions in both protein synthesis per unit RNA and RNA:protein ratio.

5. In the fed state, whole-body protein synthesis and degradation rates, whether expressed as fractional rates or amounts per unit body-weight, tended to be higher in layer than in broiler chickens. In the starved state, the difference in the rate of protein synthesis between the two strains virtually disappeared, while the degradation rates were higher in layer than in broiler birds.

6. Based on the assumed value of 3.56 kJ/g protein synthesized (Waterlow et al. 1978), the heat associated with whole-body protein synthesis in the starved state was calculated to range from 14 to 17% of the basal metabolic rate with no strain difference between layer and broiler chickens.

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. A continuous culture technique was used to study the phosphorus requirements of rumen micro-organisms. Solutions of artificial saliva containing 120, 80, 40 and 0 mg inorganic phosphorus (Pi)/1 were infused into the reaction vessels previously inoculated with rumen contents, resulting in Pi concentrations in the vessel contents of 48, 28, 4 and < 1 mg/l respectively. Various fermentative and synthetic characteristics were examined.

2. In the vessel contents, concentrations of protozoa (about 0.9 x 105/ml) were not significantly affected by pi concentration. Total volatile fatty acids (VFA) produced averaged about 6.83 mmol/h with Pi levels of 48 and 28 mg/l. Reduction in Pi concentrations to 4 and < 1 mg/l resulted in significant reductions in total VFA to approximately 6.25 and 3.75 mmol/h respectively, accompanied by a rise in pH from 6.5 to 7.3. Ammonia-nitrogen values, which averaged about 131 mg/l at the higher Pi concentrations, also increased with the lowest level of Pi to about 240 mg/l. ATP concentrations averaged about 14 μmol/l at the highest Pi concentration and fell progressively with each reduction in Pi concentration to a final value of 2.5μmol/1 with the Pi level < 1 mg/1.

3. At Pi concentrations of 48 and 28 mg/l, the digestibilities of xylose, arabinose and cellulose-glucose were maintained at about 0.90, 0.62 and 0.70 g/g input respectively. At lower Pi, concentrations these digestibilities fell significantly and corresponding values at Pi < 1 mg/l were 0.73, 0.41 and 0.31 respectively. Starch digestion was unaffected by Pi concentrations and remained at about 0.90 g/g input.

4. The amount of microbial-N synthesized averaged 0.48 g/d and was maintained with Pi concentrations down to 4 mg/l. There was, however, a significant reduction to 0.26 g/d with Pi concentrations of < l mg/l. The effiency of microbial protein synthesis was variable but averaged approximately 25 g N/kg total carbothdrate fermented.

5. It was estimated that the minimum Pi concentrations required in rumen fluid in vivo to maintain maximum degradative and synthetic microbial activities was in the range 75–100 mg/l and that the over-all P requirement of the microbes was of the order of 5.1 g/kg apparently digested organic matter intake.

1. A method was developed for extracting enzymes from micro-organisms closely associated with ammoniatreated straw (NH3-S) that had been incubated in nylon bags in the rumen. Incubation of washed straw with 125 ml carbon tetrachloride/l and 20 μg lysozyme/ml for 3 h at 37° gave carboxymethylcellulase (EC 3. 2. 1. 4; CMCase) and NAD-linked glutamate dehydrogenase (EC 1. 4. 1.2; GDH) activities greater than those extracted by sonication.

2. GDH associated with NH3-S increased with incubation time and was highest in sheep receiving a high-barley diet. Particle-bound CMCase activity reached a peak between 16 and 24 h and declined thereafter.

3. Particle-bound GDH activity showed no correlation with dry matter (DM) degradation in the rumens of sheep fed on a range of diets. In contrast, CMCase activity after 24 h was highly correlated with DM degradability of the same samples at 24 h (r 0.98) and 48 h ( r 0.94).

4. It was concluded that GDH and CMCase can be used as indices of the total population of colonizing rumen micro-organisms and of the fibre-degrading population respectively, and that these enzymes can therefore be used to assess rapidly and with great sensitivity variations in the rumen environment that affect the rate of fibre breakdown.

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.