1. The absorption of 64Cu from closed duodeno-jejunal loops in anaesthetized rats was significantly less in the presence of pancreatic juice compared with that in the presence of saline (9 g sodium chloride/1). The inhibition of 64Cu absorption caused by pancreatic juice was similar to that achieved with bile.

2. Studies using solutions of electrolytes and of pancreatic extracts showed that the inhibitory effect of pancreatic secretions was due to its protein-enzyme content and not to its bicarbonate content.

Pancreatic secretion and bile influence Cu absorption and thereby affect Cu homeostasis.

1. The nitrogen balance and creatinine excretion of wether lambs of 30–48 kg, wholly nourished by the intragastric infusion of nutrients, were measured in two experiments. Four lambs were used in each experiment. In Expt 1 a constant amount of casein was infused into the abomasum (640 mg N/kg body-weight (W)0·75 per d) and the amount of volatile fatty acids (VFA) infused into the rumen ranged from 0 to 670 kJ/kg W0·75 per d as six increments. Expt 2 was of similar design but two levels of casein were infused (530 and 1060 mg N/kg W0·75 per d) and, with each level of casein, VFA infused ranged from 0 to 700 kJ/kg W0·75 per d as seven increments.

2. Daily creatinine excretion was not constant, but varied between 2-d means with standard deviations of between 7·1 and 16·5% (average 13·1%) of the over-all means. There was an apparent correlation between creatinine excretion and the amount of energy infused in six out of eight lambs. There was no effect of the amount of casein infused.

3. In both experiments N balance was negative only when the amount of energy infused was substantially below published values for energy maintenance. In Expt 1, N equilibrium was calculated to be achieved at a gross (VFA plus protein) energy infusion level of 162 (SE 29) kJ/kg W0·75 per d. In Expt 2 it was observed that, at a given level of energy infusion, N retention was greater when the amount of energy had been increased from the previous level, than when it had been decreased.

4. It is concluded that the animal appears to allocate available amino acids to protein synthesis, rather than to oxidation, even when in negative energy balance. It is also concluded that the enhanced N retention observed when the amount of energy infused had been increased represented compensation after a period of energy restriction.

1. Proteins were labelled with 14C in a limited reductive methylation using [14C]formaldehyde and sodium borohydride.

2. The rate of hydrolysis of purified proteins was little (< 10%) affected by methylation and the 14C-labelled digestion products were not incorporated into microbial protein during a 5 h incubation with rumen fluid in vitro. It was therefore concluded that proteins labelled with 14C in this way are valid substrates for study with rumen micro-organisms.

3. The patterns of digestion of 14C-labelled fish meal, linseed meal and groundnut-protein meal by rumen micro-organisms in vitro were similar to those found in vivo.

4. The rates of hydrolysis of a number of 14C-labelled proteins, including glycoprotein II and lectin from kidney beans (Phaseolus vulgaris), were determined with mixed rumen micro-organisms and with proteases extracted from rumen bacteria. Different soluble proteins were digested at quite different rates, with casein being most readily hydrolysed.

5. Proteins modified by performic acid oxidation, by cross-linking using 1,6-di-iso-cyanatohexane or by diazotization were labelled with 14C. Performic acid treatment generally increased the susceptibility of proteins to digestion, so that the rates of hydrolysis of performic acid-treated proteins were more comparable than those of the unmodified proteins. Cross-linking resulted in a decreased rate of hydrolysis except with the insoluble proteins, hide powder azure and elastin congo red. Diazotization had little effect on the rate of hydrolysis of lactoglobulin and albumin, but inhibited casein hydrolysis and stimulated the breakdown of γ-globulin.

1. The addition of lysine hydrochloride (50 g/kg) to a diet supplemented with methionine (3 g/kg) had no effect on liver lipids when rats (Wistar and Sprague-Dawley) were fed ad lib. for 14 d. However, refeeding a diet supplemented with methionine and excess lysine hydrochloride to previously-starved rats (Wistar) for 6, 7 or 9 d, but not 3 or 4 d, resulted in liver lipid accumulation, mainly triglycerides, which was prevented by the addition of arginine, citrulline, ornithine, adenine, allopurinol or maize oil, but not by guanine, cytosine, thymine or uracil.

2. The addition of lysine hydrochloride to a methionine-supplemented diet resulted in reduced serum triglyceride levels after refeeding for 3 or 4 d and reduced serum cholesterol levels after refeeding for 3, 4 or 6 d. Serum lipids were unaffected by refeeding the diets for 7 or 9 d.

3. Since hepatic lipid accumulation was preceded by the decline in the level of serum triglycerides, one of the factors responsible for lipid accumulation in the liver might be reduced transport of triglycerides from the liver into the blood.

4. When adenine and allopurinol were added to the diet supplemented with methionine and lysine hydrochloride refed for 4 d, there was an increase in serum triglycerides. However, when this diet was refed for 7 d, with the addition of arginine, citrulline, guanine, pyrimidine bases, allopurinol or maize oil, no effects on serum cholesterol and triglyceride levels were observed.

1. For a period of 8 weeks, rainbow trout (Salmo gairdneri), mean initial weight 21 g, were given either a low-magnesium or control diet containing 0·03 and 0·58 g Mg/kg diet respectively. Both groups of trout were then given the control diet for a further 11 weeks.

2. Weight gains over the initial 8-week period were lowest in the Mg-deficient trout. Feeding the deficient fish the control diet rapidly improved growth rate until it was the same as that of the control trout.

3. Plasma Mg was significantly lower in the Mg-deficient trout at week 8. Feeding with the control diet for 11 weeks did not increase plasma Mg. Few changes were observed in the plasma concentrations of the other electrolytes.

4. Renal calcium concentrations were unaffected by dietary Mg levels. Similarly, the renal levels of phosphorus, sodium and potassium all fell within the range found in normal rainbow trout.

5. Muscle Mg concentrations were reduced in those trout given the Mg-deficient diet. Feeding with the control diet for a further 11 weeks increased muscle Mg but the level was still significantly lower than that found in trout given the control diet for 19 weeks.

6. The bone ash Mg concentration was significantly lower, and the Ca higher, in the deficient fish at week 8, when compared with the control group.

7. When compared with the value at the start of the experiment, total bone Mg fell slightly in the deficient trout over the initial 8-week period, but increased in the control group of fish. Feeding with the control diet for a further 11 weeks increased total bone Mg in both Mg-deficient trout and control trout.

8. The results show that the Mg deficiency imposed on the rainbow trout was of limited severity and almost complete recovery was obtained when the control diet was fed.

1. Immature and mature lucerne (Medicago sativa) and tall fescue (Festuca arundinacea) hays were analysed for their lignin and phenolic monomer (hydroxybenzoic and hydroxycinnamic acid derivatives) contents. These hays were given to four sheep with rumen, duodenal and ileal cannulas, and to a steer with rumen and abomasal cannulas, to investigate the extent and sites of digestion of lignin and phenolic monomers.

2. The hays and digesta samples were analysed for alkali and nitrobenzene-extractablephenolic monomers. Lanthanum oxide was used as an external marker in the digestion studies. Urine was also collected for estimates of total phenolic balance.

3. Grass hays contained greater concentrations of alkali-labile phenolic monomers than did legume hays, whereas legume hays had higher levels of nitrobenzene oxidation products. Mature tall fescue hay had greater concentrations of phenolic monomers than did immature tall fescue hay, but corresponding differences with maturity were not observed with lucerne hays.

4. There were quantitative differences between diets in the digestibilities and in the sites of digestion of phenolic monomers. Digestibilities ranged from 0·191 to 1·004 for alkali-labile compounds and from −1·137 to 0·868 for nitrobenzene oxidation products. Composition of lignin was altered during its passage through the digestive tract. The proportion of phenolic monomers not recovered in urine and faeces varied from −1·014 to 0·871 for individual compounds and differed between diets. Soluble phenolic monomers decreased in concentration as digesta passed from the rumen to the abomasum and duodenum, but increased again in the ileum; levels varied with diet. Phenolics were rapidly solubilized in the rumen after feeding.

5. Results indicate that forages differ in their phenolic monomer content and in the digestibility of these compounds. Therefore, lignin is not an inert compound in the digestive tract of ruminants as has been previously reported.

1. [125I]iodoinsulin-binding studies in the presence of a concentration range of bovine insulin were conducted to establish specific insulin-binding levels in skeletal muscle plasma membranes and isolated hepatocytes of rainbow trout (Salmo gairdneri) reared on control, high-protein or high-carbohydrate diets.

2. Negative co-operativity was observed and receptor concentrations and apparent dissociation constants established for each preparation.

3. No differences of specific binding attributed to diet were detected in skeletal muscle plasma membrane preparations; however, the receptor concentration of isolated hepatocytes from high-carbohydrate-reared trout was increased. This contrasted to comparable mammalian studies.

1. The rate of proteolysis in the rumen was dependent on the soluble protein used. With a sheep on a hay + concentrate diet the rates (approximately Vmax) for casein, Fraction I leaf protein and bovine serum albumin were 16·5, 3·4 and 0·9 mg protein nitrogen/l per min respectively.

2. Change of diet from hay + concentrate to fresh lucerne (Medicago sativa) increased the proteolytic rates for all three proteins.

3. Bovine submaxillary mucoprotein degraded extremely slowly in the rumen at approximately 0·5–0·6 mg N/l per min and its sialic acid component was degraded at a similar rate to that of the protein chain.

4. Uniformly14C-labelled Fraction I leaf protein was used to demonstrate that in the presence of a second protein, competition for enzymic sites occurred. In Fraction I and bovine serum albumin mixtures, reduced rates for the individual proteins of the mixture were observed compared with the proteins treated separately.

5. Treatment of bovine serum albumin with dithiothreitol (0·2 g/l) to cleave disulphide bridges increased the rates of proteolysis by as much as 8·5-fold.

1. Studies of anaemia and tissue iron distribution were carried out in copper-deficient rats and pair-fed control animals given Fe orally or parenterally in varying doses.

2. The anaemia of Cu deficiency was partially but incompletely corrected by oral Fe supplementation of one-to five-fold normal dietary levels or by intramuscular Fe supplementation.

3. Serum Fe increased in Cu-deficient animals as the dose of supplemental Fe was increased.

4. Hepatic Fe accumulation occurred in Cu-deficient rats which were administered with either oral Fe in two-to five-fold excess or low doses of intramuscular Fe. This difference was not seen in animals receiving high doses of intramuscular Fe, but similar relativedifferences were seen in Cu-deficient and Cu-replete rats which had been given no Fe supplementation.

5. Duodenal Fe was not increased in Cu deficiency. Bone marrow Fe was present in Cu-deficient animals receiving either parenteral or oral Fe supplementation.

6. Present studies suggest that a decrease in caeruloplasmin (EC 1. 16. 3. 1) activity does not wholly explain the anaemia of Cu deficiency.Fe accumulation may be restricted to the liver, suggesting that Cu may be required for normal intracellular Fe metabolism.

1. Emulsions of C18 unsaturated fatty acids (FA) were infused for 2 h into the intestine of conscious sheep while motility of the reticulum and rumen was recorded.

2. Statistically-significant depression of motility was found when 3 or 5 g FA/h were infused. At 1 g/h there were minor disruptions of motility.

3. The inhibitory potency was not related to the extent of unsaturation of the FA.

4. Receptors mediating the inhibitory effect were postulated to be distal to the iliac flexure of the duodenum, but the possible role of bile and pancreatic juice is discussed in relation to this problem.

5. The probability that the effect was hormonally mediated is discussed.

1. Mixtures of skim milk and free amino acids were compared as diets for pigs which would allow manipulation of dietary amino acid levels. Piglets gained 208 g/d between 3 and 14 d of age on the skim-milk diet, but replacement of 600 g/kg of the dietary nitrogen with free amino acids reduced growth rate to 148 g/d.

2. Supplementation of a lysine-deficient diet with lysine reduced the catabolism of [14C]phenylalanine showing that phenylalanine catabolism could be used as an indicator of the adequacy of diet with respect to another essential amino acid.

3. The dietary level of phenylalanine which would provide an excess for catabolism by the piglet was estimated directly by measuring the influence of dietary phenylalanine level on [14C]phenylalanine oxidation. Reduction of the dietary phenylalanine level below 7 g/kg had no effect on phenylalanine oxidation, whereas increasing the dietary phenylalanine level above 7 g/kg resulted in a linear increase in phenylalanine oxidation.

4. An indirect estimate of histidine requirement was made by examining the influence of dietary histidine level on [14C]phenylalanine oxidation. In diets containing more than 4 g histidine/kg, phenylalanine oxidation was minimal. In diets containing less than 4 g histidine/kg, [14C]phenylalanine oxidation increased as the level of dietary histidine was reduced. This showed that the utilization of the essential amino acid phenylalanine, for protein synthesis, was not limited by histidine supply in diets containing more than 4 g histidine/kg.

5. A direct estimate of histidine requirement was made by examining the influence of dietary histidine level on [14C]histidine oxidation. Diets with more than 4 g histidine/kg contained an excess which was catabolized: there was a linear increase in histidine oxidation in response to dietary histidine levels greater than 4 g/kg. This confirmed the previous indirect estimate of histidine requirement.

1. The voluntary food intake, during 30 min periods after morning and afternoon feeds and during 24 h, by growing pigs given diets containing rapeseed meal (Rsm) or soya-bean meal (Sbm) as the only protein supplement was determined. One diet was offered at a time and a daily changeover sequence of feeding was followed.

2. Four rapeseed meals were compared, one from seeds of British-grown winter Brassica napus varieties (Brsm) and the others from seeds of the var7ieties Tower (Trsm), Erglu (Ersm) and Span (Srsm). The effects on feed intake of adding flavouring substances to the Brsm diet were also determined. The flavouring substances were molassine meal, sucrose and four commercially-available substances: P, pig nectar; H, hog nectar; S, sow nectar and A, apple.

3. Intake of the Brsm diet was significantly less than those of the Sbm, Trsm and Ersm diets.

4. Addition to the Brsm diet of molassine meal or sucrose at 50 or 100 g/kg did not improve voluntary feed intake. None of the commercial flavouring substances raised the intake of the Brsm diet to the level of the Sbm diet but they improved intake of the Brsmdiet to varying extents. Flavourings H, S and A gave similar improvements which were substantial.

5. The Sbm, Brsm and Trsm diets were each fed ad. lib. to groups of growing pigs continuously for 4 weeks. Weekly feed intakes and weight gains were determined. Feed intakes and weight gains followed closely the intake values obtained in the changeover experiments. The highest values were for the Sbm diet; those for the Trsm diet were slightly lower and those for the Brsm diet were substantially and significantly lower.

6. The glucosinolate, sinapine and tannin contents of the rapeseed meals were determined and the results suggested that voluntary feed intake of diets containing these meals was related to their glucosinolate content, but not to their sinapine or tannin contents.

1. Clun Forest ewes with single and twin lambs were exposed to neutral (20°) or cold (−1°) environmental temperatures, beginning soon after parturition, for 4 d. The intakes of milk, lactose and glycerides by the lambs were calculated from measurements of the rate of displacement of tritiated water (injected into the lambs) by non-radioactive water in milk from the ewes, and measurements of the concentration of lactose and glyceride glycerol in small samples of milk.

2. The yield of milk from ewes bearing twin lambs was greater than the yield from single-bearing ewes in the neutral environment but, in both environments, twin lambs had lower intakes of milk and milk lactose and glycerides, and gained body-weight more slowly, than single lambs. Milk from twin-bearing ewes had a lower lactose concentration than milk from single-bearing ewes.

3. Cold exposure reduced the intake of milk and milk lactose, and reduced the rate of weight gain, of single and twin lambs. Glyceride intake was not different in the two environments.

4. There appears to be a conflict between reduced supply of milk by the ewe and increased demand for milk by the lamb in cold temperatures. Such a conflict is sharpened when twin lambs are born.

1. Piglets were weaned at 3 d of age and were introduced to liquid diets in which 400 g/kg protein was supplied as skim-milk powder and the balance as a mixture of free amino acids. The skim milk contributed 2·3 g methionine and 1·4 g cystine/kg diet; the experimental diets were made by supplementing these levels with free amino acids.

2. The adequacy of the test level of the amino acid in the diet was assessed by measuring the oxidation of [1−14]phenylalanine as an indicator of the partition of the essential amino acids between incorporation into protein and degradation. Radioactivity recovered as carbon dioxide was used as a measure of catabolism.

3. Addition of 0·2, 0·4, 0·7, 1·2 and 1·7 g L-methione/kg to a diet containing 5 g cystine and 3 g choline chloride/kg showed that phenylalanine catabolism was minimal for the diet with 2·7 g methionine/kg indicating that this is the dietary requirement for methionine to serve as a source of methionine residues for protein synthesis.

4. Addition of D-methionine to produce a series of diets with graded levels of methionine showed that the D-isomer was less effective than the L-isomer in reducing phenylalanine catabolism: the addition of 0·8 g D-methionine/kg diet was needed to produce the same effect as 0·4 g L-methionine/kg diet showing that the replacement value of D-methionine for L-methionine was 50% in the young pig.

5. To investigate the influence of cystine on methionine requirement, diets with varying levels of methionine and cystine were prepared. Oxidation of [U-14C]methionine was used as an indication of an excess of methionine, and the results showed that increasing the dietary methionine level above 3·0 g/kg in diets containing 1·4 g cystine/kg provided an excess of methionine for oxidation. This indicated a sulphur amino acid requirement of 4·4 g/kg, one-third of this being supplied as cystine.

1. The catabolism of [14C]phenylalanine was used to indicate the effects of varying the dietary level of lysine and threonine on the retention of dietary amino acids by 2-week-old pigs receiving diets containing skim milk and a mixture of free amino acids.

2. Reducing the dietary level of lysine from 16 to 12 g/kg had no influence on phenylalanine oxidation, reducing the lysine level from 12 to 11 then to 10 g/kg caused an almost linear increase in phenylalanine oxidation whereas further reduction to 9 or 8 g/kg resulted in a less-marked increase in phenylalanine oxidation. This showed that 12 g lysine/kg was required to maximize amino acid retention and indicated that lysine was conserved more effectively at low dietary concentrations than at dietary concentrations approaching the requirement.

3. Reducing the dietary level of threonine from 8 to 6 g/kg had no influence on phenylalanine oxidation, whereas further reduction to 4 g/kg caused a linear increase in phenylalanine catabolism showing that 6 g threonine/kg was required to maximize amino acid retention.

4. Reduction of the levels of lysine, threonine and methionine from the generous levels characteristic of a diet containing 240 g protein from skim milk/kg, to the requirement levels determined separately in the presence of the generous levels of all the other amino acids, resulted in a twofold increase in phenylalanine catabolism. This shows that the pig seems able to conserve limiting intakes of a single amino acid, but not if the intakes of two or three amino acids are limiting.

1. The fractional rates of loss of 14C and body-weight were measured in growing female rats after a single dose of [1-14C]methionine. After the dose, the rats were maintained for 30 d on diets containing graded amounts of methionine and killed at 30 d.

2. By 20 d after the dose the level of labelling of body proteins was fairly uniform. From 20 to 30 d, 14CO2 was collected at intervals. The rats were killed at 30 d and the total radioactivity remaining in the body was measured.

3. The fractional loss of 14CO2 between days 20 and 30 was constant regardless of methionine intake except at the highest intake level.

4. After correcting the fractional loss of 14CO2 for urinary 14C loss, a value of 35 mg/kg body-weight (20 mg/kg body-weight0·75) was obtained for the rate of endogenous methionine oxidation.

1. Phytase (EC 3.1.3.8) concentration has been measured in the small intestineof rat, rabbit, guinea-pig and hamster. Levels varied from 0·12 units (μg phosphorus released/min)/mg protein in the rat to 0·03 units/mg protein in the rabbit.

2. The enzyme is localized in the brush border of the small intestine of the rat.

3. It is suggested that the levels and location of phytase are an important factor inthe uptake of metals from metal–phytate complexes. Metal ions released in the immediate vicinity of the absorptive surface of the intestine could be absorbed before being rendered insoluble by competing reactions such as hydrolysis.

1. The loss of body water of eight sows in the 7 d following weaning was determined using the deuterium oxide dilution technique. Four of the sows had received a concentrate diet in restricted amounts while the other four had been given the same diet mixed with two-thirds its weight of oat husks ad lib. during the whole of the preceding lactation. Certain blood and urine constituents were also measured.

2. Loss of body water was significantly less (P < 0·05) than weight loss of fasted animals, but body water losses were considerable in six of the eight animals.

3. Excretion of urinary nitrogen, urea and creatinine and levels of plasma urea were higher, while levels of plasma non-esterified fatty acids and the hydroxyproline index were lower 1 week after weaning compared with values obtained on the day following weaning.

4. These results indicate that in addition to water loss, depletion of body tissue, including protein, occurs in the newly-weaned sow.

1. The influence of three diets ((1) high-fibre–low-fat, (2) low-fibre–high-fat, (3) commercial breeding diet) on the concentration of short chain fatty acids (SCFA) has been investigated in male and female rats up to 14 weeks of age.

2. Hydrogen was detected in respired gas in all rats with no significant differences between diets or sex. Methane was detected only in control-fed rats at 12 weeks of age and thereafter. Caecal contents contained higher concentrations of SCFA than were found in faeces. There were no significant differences in the total faecal SCFA excreted by rats on the three diets. The proportions of SCFA in the caecum and faeces were influenced by diet.

3. The production and excretion of hydrogen, methane and SCFA in the rat appeared to reflect different aspects of bacterial metabolism. Comparison of caecal and faecal SCFA may indicate differential absorption from the colon or differential metabolism by bacteria or colonic mucosa which may be influenced by diet.

1. Absorption of 14C-labelled retinol was determined along the gastrointestinal tract of chicks, using 141Cerium as a non-absorbed reference substance, as influenced by high dietary vitamin A and the addition of tocopherol to the diet.

2. The site of major vitamin A absorption was the proximal small intestine and high intake of vitamin A reduced slightly the percentage over-all absorption.

3. Labelled glucuronides were secreted into the duodenum and were 50–60% reabsorbed in the small intestines. High-vitamin-A intakes enhanced the duodenal flow of retinyl glucuronides.

4. In vitro hepatic retinol esterification and glucuronide production were enhanced in chicks given high dietary vitamin A.

5. Plasma transport and clearance of retinol were enhanced by feeding high levels of vitamin A and further enhanced when tocopherol at high concentrations was present in the diet.

6. Dietary tocopherol had no effect on absorption, increased hepatic vitamin A stores and in vitro retinol esterification, and decreased retinyl glucuronide flows through the duodenum.