1. Effects of sodium hydroxide treatment on intake and digestion of straw organic matter (OM), and microbial protein synthesis were examined in comparison with untreated and treated straws.

2. Intakes (kg dry matter (DM)/d) of untreated, NaOH- and sodium carbonate-treated straws were 5.21, 7.04 and 6.48 respectively and intakes (kg/d) of digestible organic matter (DOM) for the respective diets were 2.57, 3.73 and 2.98 respectively. NaOH-treated straw ranked higher than untreated straw in intakes of DM and DOM (P < 0.01).

3. The proportion of DOM intake that was apparently digested in the rumen was 0.74, 0.77 and 0.66 on untreated, NaOH- and Na2CO3-treated straws respectively.

4. Although the amount of bacterial N leaving the abomasum was higher with NaOH-treated than with untreated straw (74.6 v. 56.8 g/d, P < 0.01), efficiencies of bacterial N synthesis were not different between these treatments (28.6 v. 31.5 g bacterial N/kg OM apparently digested, P > 0.05).

5. The live-weight gain which the NaOH-treated straw could support was predicted to be 350 g/d and it was concluded that a protein supplement would have provided further increase in production in diets based on NaOH-treated straw.

1. Forty-eight Friesian entire male cattle, with an initial live weight (LW) of 135 kg, were used in two experiments to measure the response to increasing levels of dietary protein (9–11 and 7.5–10.5 g nitrogen x 6.25/kg LW0.75) at differing energy levels (800–900 kJ metabolizable energy (ME) kg LW0.75) over 120-d periods. Digestibility and N balance measurements were also made during the experiments. The diets, which were based on barley and soya-bean meal, were individually fed twice daily.

2. In a third experiment, similar diets were given to four similar animals fitted with intestinal cannulas, at constant energy intake but with variations in dietary protein of 7.5–13.5 g N x 6.25/kg LW0.75. Chromic oxide paper was used as a digesta marker.

3. Positive responses in LW gain and N balance to additional protein were found in both experiments but these were significant (P < 0.05) only in the second experiment and were associated with significant (P < 0.01) increases in the digestibility of modified acid-detergent fibre and ME intake.

4. Mean values, which were not significantly different between treatments, for the degradability of dietary protein in the rumen and the efficiency of microbial protein synthesis were 0.57 and 31.3 g/kg organic matter apparently digested in the rumen respectively. Corresponding values obtained by regression analysis were 0.56 and 28.2.

5. The results in general support the Agricultural Research Council (1980) proposals and suggest that undegraded dietary protein was not limiting in these experiments but that rumen-degradable protein levels were limiting on some treatments.

6. Regression analysis indicated that the mean response to additional protein (g LW gain/g N x 6.25) per kg LW was 0.52 in Expt 1 and 0.51 in Expt 2. These responses could be largely explained by increases in ME intakes.

7. Measurements of duodenal amino acid flow showed marked increases in essential amino acids (EAA) across the rumen. However, EAA flows, were not significantly increased at higher N intakes suggesting that protein per se was not limiting in these experiments.

1. Chicks and turkey poults were fed for 3 weeks on low-zinc diets, prepared from purified ingredients, supplemented with zinc oxide at graded levels.

2. Birds of both species given the unsupplemented basal diets grew poorly, with high mortality rates. All had severe hyperkeratosis but bone development was normal. Only when birds received diets with low concentrations of added Zn were leg abnormalities observed.

3. Zn requirements were assessed visually from dose-response graphs. The chick required 18 mg Zn/kg diet for maximal live weight and 24 mg Zn/kg for maximal Zn concentration in blood serum. The responses of tibial Zn and net retention of Zn did not reach plateaux within the range of dietary Zn concentrations studied. The turkey poult's Zn requirement for maximal live weight was 25 and 28–29 mg/kg for net retention of Zn and for maximal concentration of Zn in blood plasma and in the tibia; 41 mg Zn/kg diet was required for maximal Zn in blood serum.

4. Liver Zn was not correlated with dietary Zn in either species.

1. Intestinal radiocalcium absorption was measured in goats by a double-isotope technique involving injection of 45CaCl2 intravenously and 47CaCl2 into the abomasum. Cumulative absorption of radiocalcium was calculated by deconvolution analysis form curves of plasma radioactivity.

2. Repeated measurements at 2 d intervals gave highly reproducible results (r 0.94, P < 0.001). No systematic difference between two consecutive measurements was observed. A good agreement between absorption of radiocalcium from simultaneously administered 47CaCl2 and 45Ca-labelled hay (r 0.93, P < 0.001) seems to justify the use of inorganic 47Ca as a tracer for Ca in ruminant diets.

3. Two- to three-fold increases in radiocalcium absorption 48 h after oral treatment with 1,25- dihydroxycholecalciferol or leaves of Solanum malacoxylon showed the usefulness of the method in situations of rapidly changing Ca absorption.

4. Endogenous adaptations in intestinal radiocalcium absorption from 20 to 43% were observed in lactating goats when Ca intakes decreased from 12 to 4 g/d.

5. It is concluded that the double-isotope technique is a suitable method for studies of Ca absorption in ruminants when tracer is introduced into the abomasum. The test is completed in 3–4 h and may therefore be used in situations where the absorption of Ca undergoes rapid changes.

1. The effect of body fatness on the fasting heat production and energetic efficiency of adult sheep was studied.

2. Energy balance and heat production were determined in adult wether sheep at three fatness levels given a diet of grass hay and maize at four feeding levels, including fasting, in open-circuit respiration chambers. The sheep weighed approximately 60 kg at the start and were fed over a period of 4–7 months to obtain one of three levels of bodyfatness: fat 90 kg, medium 70 kg and thin 55 kg.

3. Neither the digestibility nor the metabolizability of the diet was affected by body fatness or feeding level.

4. Average fasting heat production was 6.47, 7.00 and 8.20 MJ/d for the thin, medium and fat sheep respectively, but when expressed as a multiple of metabolic body size (kg W0.75) remained constant at 0.31 MJ/kg W0.75.

5. At each level of feeding the fat sheep produced most heat, but when heat production was expressed as a multiple of fasting heat production or metabolic body size, the differences due to level of fatness disappeared. Heat increment was not affected by fatness and there was no suggestion that energy utilization was improved by loss of condition.

6. It is concluded that white adipose tissue is highly active and contributes significantly to the maintenance energy requirements of adult sheep. Metabolic body size is a good unit of reference for comparison of energy metabolism in adult animals of the same species but varying in body size.

1. Intestinal absorption of 47Ca was measured by a double-isotope technique in goats treated with 1, 5 or 25 μg of 1,25-dihydroxycholecalciferol (1,25(OH)2D3). The effects of giving 1,25(OH)2D3 by intravenous (iv) infusion for 30–36 h were compared at each dose level with the effects obtained by oral administration of 1,25(OH)2D3 either in ethanol or protected against rumen degradation in fatty acid pellets.

2. Dose-dependent increments in absorption followed the treatments, with a doubling of absorption at the 1 μg dose and three- to fivefold increases with the 5 and 25 μg doses. 47Ca absorption was equally stimulated 2 and 6 d after treatment but had returned to pretreatment levels 12–14 d after treatment.

3. Intravenous and protected oral administration of 1,25(OH)2D3 stimulated 47Ca absorption to the same extent, in spite of two- to fivefold higher plasma concentrations of 1,25(OH)2D3 after iv treatment. Somewhat lower increments in 47Ca absorption were seen using ethanol as the vehicle for oral administration.

4. The naturally occurring metabolites 1,24(R),25-trihydroxycholecalciferol and 1,25(S),26-trihydroxy-cholecalciferol had only one-tenth to one-fifteenth the potency of 1,25(OH)2D3 in stimulating 47Ca absorption, while synthetic lα-hydroxycholecalciferol appeared to be twice as effective as 1,25(OH)2D3 when tested at a high (10μg) dose.

1. The dietary intake of male mice from a line selected for high body-weight was restricted to 60% by weight of the ad lib. intake of the control litter-mates between days 21 and 42 post partum.

2. One group was killed and compared with controls at 42 d of age. A further group then resumed ad lib. feeding. Mice which had regained the control body-weight by 61 d of age were killed and also compared with controls.

3. Muscle weight, fibre length, sarcomere length, sarcomere number per fibre, actin length and myosin length were measured in the biceps brachii and tibialis anterior muscles.

4. Muscle weight, fibre length and the number of sarcomeres per fibre were significantly reduced in both muscles following dietary restriction, but regained their control values following a resumption of normal feeding. The other indices remained unchanged throughout the study.

5. The pattern of fibre length changes, due entirely to alterations in sarcomere number, is similar to that reported previously during growth, senescence and immobilization and following selection for high and low body-weights.

1. Two nitrogen-balance experiments were performed with growing rats to test the effect of dietary fibre level, protein quality and antibiotic inclusion on microbial activity, N excretion patterns and energy digestibility. Each experiment involved eight dietary treatments in a 2 x 2 x 2 factorial design, with five rats per treatment. The eight treatments resulted from a combination of two protein treatments, two fibre treatments and two antibiotic treatments. In Expt 1 the protein was provided as barley, or barley plus 2 g L-lysine hydrochloride/kg dry matter (DM) (at 15 g N/kg DM) and in Expt 2 as soya-bean meal or soya-bean meal plus 2 g DL-methionine/kg DM (at 15 g N/kg DM). In both experiments the basal diet was provided with or without additional fibre as 100 g barley husk/kg DM and with or without antibiotic as 7 g Nebacitin/kg DM.

2. With both barley and soya-bean meal, true protein digestibility (TD) was improved with the addition of amino acids. Only with the soya-bean meal diets was TD increased with Nebacitin treatment, with the effect of Nebacitin and methionine being additive. Barley husk slightly reduced the TD of soya-bean meal.

3. The effect of treatments on biological value (BV) was considerable. Lysine increased BV of the barley diet from 0.741 to 0.815 whereas Nebacitin reduced BV from 0.799 to 0.757. Methionine increased the BV of soya-bean meal from 0.754 to 0.911 while BV was reduced by Nebacitin from 0.843 to 0.821 and by barley husk from 0.845 to 0.820.

4. Net protein utilization (NPU) was markedly improved by the addition of amino acids and reduced by the addition of Nebacitin. Barley husk reduced NPU with soya-bean meal diets only.

5. Amino acid addition had no effect on energy digestibility of either diet, but Nebacitin reduced this value by approximately 5% on the barley diets, with a smaller reduction on the soya-bean meal diets. Fibre reduced energy digestibility of both diets.

6. On both diets, blood urea (BU) decreased with addition of amino acids. Nebacitin increased BU with the barley diets, but decreased BU with the soya-bean meal diets. With the soya-bean meal diets, the decrease with a combination of barley husk and methionine was particularly marked.

7. Microbial activity, as measured by caecal ATP activity, was strongly reduced by antibiotic addition with both protein sources. On the soya-bean meal diets ATP activity was increased by the addition of methionine.

8. The results demonstrated a difference in response to the addition of fibre and the first limiting amino acid to barley and soya-bean meal, as measured by several indicators of protein and energy utilization.

1. Voluntary intake was determined with vegetative Lotus pedunculatus cut and fed fresh to growing sheep of 42–46 kg live weight. Effects attributable to condensed tannins were assessed by growing the plant under high and low levels of soil fertility, inducing low and high concentrations of tannin (Expt 1), or by binding the tannins through spraying the herbage with polyethylene glycol (molecular weight 3350, PEG; Expt 2). Primary-growth lotus was used in Expt 1 and secondary-growth lotus in Expt 2. Concentrations of total and free condensed tannin were determined in fresh lotus, free tanning being defined as that not bound by mascerates of the plant.

2. In Expt 1 the herbages fed contained respectively 46 and 106 g total condensed tannin/kg dry matter (DM) and 3 and 14 g free condensed tannin/kg DM. Mean metabolizable energy (ME) intakes were 0.89 and 0.77 MJ/kg live weight0.75 per d (P < 0.05) respectively.

3. The lotus used in Expt 2 contained 63 and 5 g total reactive condensed tannin and free condensed tannin/kg DM respectively. After spraying with PEG at 2.4 g/g total condensed tannin, these values were reduced to 7 and 0.5 g/kg DM respectively. PEG addition increased apparent digestibility (proportion of each nutrient ingested) of cellulose, hemicellulose and nitrogen by 0.05, 0.08 and 0.26, and increased ME intake from 0.48 to 0.69 MJ/kg live weight0.75 per d.

4. It was concluded that high concentrations of condensed tannins depressed ME intake, due to depressions in both the voluntary intake and digestion of organic matter. The stimulation of hemicellulose and cellulose digestion by PEG addition suggests that the condensed tannin was depressing rumen digestion.

5. It is considered that free tannins are most likely to have been responsible for the depressive effects in the present study. This could be due to their reaction with microbial enzymes in the rumen, the tannin content of the plant exceeding the capacity of the plant protein to bind it, or to reaction with enzymes secreted into the small intestine following the absorption of amino acids. In either instance free tannins could also react with proteins of the gut wall.

1. Primary growth vegetative Lotus pedunculatus containing 46 and 106 g/kg dry matter (DM) of total condensed tannin and 3 and 14 g/kg DM of free condensed tannin, was cut and fed fresh at hourly intervals (750 g DM/d) to sheep fitted with permanent cannulas into the rumen and duodenum. Low- and high-tannin lotus contained respectively 41.3 and 31.6 g total nitrogen/kg DM and 132 and 152 g lignin/kg DM. The two forms of lotus were similar in carbohydrate composition.

2. Nutrient intake was recorded and faecal output measured by direct collection. Digesta flow to the duodenum was estimated by measuring dilution at the duodenum of inert ruthenium phenanthroline (Ru-P) and chromium-EDTA markers continuously infused into the rumen.

3. Effects attributable to condensed tannins were assessed by comparing the digestion of the two diets, and by comparing the digestion of each with predicted values for non-tannin-containing fresh forages fed at similar intakes.

4. Apparent digestibility of all nutrients measured was less for high- than for low-tannin lotus (P < 0.01). The levels of cellulose digested ruminally and post-ruminally in both forms of lotus were similar to predicted values. However, less hemicellulose and readily fermentable carbohydrate (RFC; soluble carbohydrate + pectin) was digested in the rumen in sheep given both forms of lotus than would be predicted for non-tannin-containing fresh forage diets, but this was compensated for by greater post-ruminal absorption of both nutrients.

5. Total N gains across the rumen (duodenal N flow – total N intake) were 1.8 and 10.5 g/d for low- and high-tannin lotus v. predicted losses of 3.7 and 2.1 g/d for non-tannin-containing fresh forages given at the same total N intakes. Post-ruminal digestion of non-amonia-N (NAN; proportion NAN flowing at duodenum) was 0.71 and 0.67 for low- and high-tannin lotus respectively v. 0.76 for comparable non-tannin-containing fresh forages. Energy absorbed as amino acids from the small intestine was calculated to be 0.29 of metabolizable energy for both forms of lotus, compared with 0.17 and 0.21 for perennial ryegrass and white clover.

6. It was concluded that the presence of condensed tannins in lotus markedly increased post-ruminal NAN absorption compared with non-tannin-containing fresh forage diets, but depressed ruminal digestion of RFC and hemicellulose.

1. Concentrations of reducing sugars, glucose, fructose and lactic acid in blood obtained from arterial and portal catheters were measured for periods of 8–24 h in twenty-three unanaesthetized pigs (mean body-weight 50 kg). From 6 to 8 d after implantation of catheters, the animals received experimental meals containing different levels (400, 800, 1200, 1600 g respectively) of different sugars (glucose ten meals, sucrose eighteen meals, lactose nine meals, maize starch sixteen meals) as well as a protein–mineral–vitamin premix.

2. After each meal the reducing sugars appeared in the portal blood in successive waves. The porto-arterial differences in the concentration of reducing sugars, representing the real appearance of sugar-hydrolysis products in the animal, varied greatly according to the sugar ingested and its level of intake. For each level of intake, these differences were larger, but of shorter duration, for glucose and sucrose than for maize starch. For these three carbohydrates, the higher the level of ingestion, the larger and the more persistent the porto-arterial differences. Lactose represented a special case, as the porto-arterial differences of reducing sugars were always much lower than those obtained with the other sugars and they did not vary with the level of intake.

3. Our findings show that the products formed by feeding glucose and sucrose appear more rapidly in the portal blood than those formed by feeding lactose. Accordingly, the length of time of digestion of glucose and sucrose is shorter than that of maize starch and lactose.

1. Concentrations of reducing sugars, glucose, fructose and lactic acid in blood obtained from arterial and portal catheters were measured together with the portal hepatic blood flow-rate for periods of 8–24 h in twenty-six unanaesthetized pigs (mean body-weight 51 kg). The animals received experimental meals containing different amounts (100–1600 g) of different sugars (glucose fifteen meals, sucrose twenty-four meals, lactose fourteen meals, maize starch nineteen meals) together with a protein–mineral–vitamin mixture (150 g) 6–8 d after implantation of the catheters and an electromagnetic flow probe.

2. Because the portal blood flow pattern did not differ between test meals, net absorption followed the same trends as for porto-arterial concentration differences (Rérat et al. 1984). Apart from lactose, the amounts of reducing sugars appearing in the portal vein correlated with the intake of the test meal, but the absorption pattern was different for each sugar. The appearance of reducing sugars was faster and earlier after intake of glucose than after sucrose and the same was the case for sucrose relative to maize starch. The differences between the three carbohydrates tended to increase with the level of intake.

3. With a test meal containing 1 kg carbohydrate, i.e. a normal meal in a 50 kg pig, digestion of sucrose and maize starch was not finished 8 h after the meal since only 60 and 52% respectively of their hydrolysis products were recovered in the portal blood. In the case of lactose, the amounts of reducing sugars appearing in the portal blood were always very small and constant (113–118 g within 8 h) whatever the level of intake, i.e. 30 and 15% of their hydrolysis products for intakes of 400 and 800 g respectively.

4. Depending on the carbohydrate ingested, the uptake of glucose by the gut cell wall ranged from 14 to 21 g/h and the production of lactic acid from 2.5 to 3.5 g/h.

1. 15N-labelled mixed rumen bacteria, obtained from a steer that had received [15N]urea in its diet, were disrupted ultrasonically and freed from nucleic acids and their degradation products. Samples were subjected to a simulated abomasal digestion with pepsin.

2. The digests were infused with a non-absorbable marker (polyethylene glycol) into the duodenum of four steers equipped with simple duodenal and re-entrant ileal cannulas and adapted to a diet of barley straw, flaked maize and urea. The outflow from the ileum was collected for 6–7 h. The mean value for the digestibility of 15N bacterial proteins in the small intestine was estimated to be 0.74.

3. [14C]urea was administered intravenously during the infusion of the 15N-labelled protein into the duodenum. Urine and faeces were collected for the next 48 h and the proportion of urea-N produced, that was excreted in the urine, estimated from urine 14C excretion. Total urea 15N production was estimated from this value and the amount of 15N excreted in the urine. The mean proportion of 15N absorbed that was deposited in body protein, 0.70, was calculated by difference. The over-all efficiency of utilization of 15N in the infused rumen bacterial protein was 0.52.

4. An approximate estimate of the mean rate of protein synthesis calculated from the data was 24 g/kg body-weight (W)0.75 per d and compared with an estimated net deposition of protein of 1.67 g/kg W0.75 per d.

5. The importance of these values in factorial schemes for estimating ruminant N requirements is discussed.

1. Two experiments were conducted to evaluate the effects of caecectomy and source of dietary fibre and starch on excretion of amino acids by laying hens. In Expt 1, caecectomized hens excreted significantly higher levels of several amino acids than intact hens during a 24 h fasting period. These differences were greatest for threonine, proline and leucine.

2. In Expt 2, caecectomized and intact hens were given either a nitrogen-free diet containing 500 g cellulose/kg or one containing 400 g uncooked potato starch/kg and 100 g citrus pectin/kg. The potato starch-pectin (PSP) diet increased excretion of most amino acids by both caecectomized and intact hens compared with the cellulose diet, with this response being larger for intact hens. When compared across diets, caecectomized hens excreted more threonine and serine than intact hens.

3. Excreta voided by hens given PSP contained higher levels of alanine and valine and lower levels of aspartic acid, glutamic acid and methionine than excreta from the cellulose diet. When compared across diets, excreta from caecectomized hens contained more threonine, serine and isoleucine and less aspartic acid and alanine than excreta from intact hens.

4. Multiple regression analyses of excreta amino acid profiles on profiles of endogenous and microbial protein suggested that the intestinal microflora had greater influence on amino acids excreted by caecectomized hens than on those excreted by intact hens.