1. Differences in the extent of breakdown of phytate in wholemeal and white flours prepared from three wheats when the flours were made into bread using the three main UK commercial breadmaking processes were investigated.

2. The extent of breakdown (31–46% for wholemeal breads, 88–99% for white breads) was not proportional to the relative processing times involved (1–4 h). The importance of destruction of phytate in the oven is stressed.

3. The phytase (myo-inositol hexaphosphate phosphohydrolase. EC 3.1.3.8) activities of the wholemeal flours and of the yeast were determined. Re-examination of some information in the literature enabled the relative importance of these activities, and of the various stages of breadmaking, in determining the extent of hydrolysis of phytate to be assessed.

4. Average values for the molar ratio, phytate: zinc, of 22:1 and 0.8:1 were calculated for wholemeal and white breads respectively. The nutritional significance of these results is discussed.

1. Protein turnover and muscle composition has been studied in rat skeletal muscle throughout development in a relatively-fast-growing rat strain.

2. Muscle growth involved an increase in the total DNA and in the DNA-unit size as indicated by protein: DNA. As a result of the latter increase together with no change in RNA: DNA, the RNA concentration fell throughout development.

3. Rates of protein synthesis measured in vivo by the continuous intravenous infusion method fell throughout development from 15.6%/d at 25 d to 4.46%/d at 320 d, and these changes reflected mainly the fall in RNA concentration, since there was no marked change in the rate of protein synthesis per unit RNA.

4. The rate of protein degradation, measured as the difference between rates of protein synthesis and growth, fell from 9.82%/d at 25 d to 4.46%/d at 320 d.

5. When these changes in protein turnover throughout development are compared with measurements made previously in a slow-growing strain it would appear that the faster growth was achieved as a result of increased efficiency of protein synthesis (defined as net synthesis: over-all synthesis) and this occurred mainly because of lower rate of protein degradation.

1. A method of studying zinc absorption in rats has been developed in which binding of radioactive Zn to the intestinal mucosa and absorption into the carcass was determined at different times after administration by stomach tube.

2. This technique has been used to evaluate different hypotheses concerning the control of Zn absorption and to examine the processes by which this occurs.

3. The proportion of radioactive Zn absorbed into the carcass was found to be dependent on the Zn status of the animals but that found within the small intestinal wall was independent of this, indicating the existence of two mechanisms of Zn absorption.

4. One of these two mechanisms has been shown to be induced by a low dietary Zn content while the other was shown to be insensitive to this. This latter mechanism predominated in rats of normal dietary Zn status and a study of the characteristics of this process indicated that the quantity of Zn absorbed was proportional to the dietary Zn content over the normal range of intake. This implies that normally Zn homeostasis in rats is achieved through variations in Zn excretion. The additional mechanism of Zn absorption only becomes fully active at levels of dietary Zn below 0.24 μmol/g diet.

1. Brain hypothalamic concentrations of serotonin and norepinephrine have been implicated in the control of food intake. During pregnancy and lactation a rat dam's food consumption is increased and so a study was performed to ascertain whether this was associated with changes in the hypothalamic content of serotonin and norepinephrine.

2. In the first experiment, forty-eight Sprague Dawley rat dams were given a diet containing 250 g casein/kg adlib. After 2 weeks, eight were killed and their hypothalamic analysed for the previously-mentioned neurotransmitters. The rest were mated and continued on the diet. On each of days 7, 14 and 20 of gestation, day 14 of lactation and 2 weeks after weaning of their pups a further eight dams were killed and their hypothalami assayed as described previously. Food intake was monitored throughout the experimental period.

3. The increased food intake of the dams during gestation and lactation increased to the same extent as elevations in hypothalamic norepinephrine content and depressions in serotonin content. After lactation food intake returned to pre-pregnancy levels as did the hypothalamic levels of norepinephrine and serotonin.

4. By using the same experimental design but limiting the increase in food intake in pregnancy and lactation to half the expected amount the same changes were found in hypothalamic norepinephrine and serotonin contents.

5. The possibility of hypothalamic neurotransmitter contents controlling food intake is discussed.

1. The rate of proteolysis of fraction 1 (18S) leaf protein in the rumen of sheep and cattle was affected by diet and the rate on fresh lucerne (Medicago sativa L) was three to nine times the rate on a hay + concentrate diet.

2. Simultaneous rumen fermentations in vivo and in an artificial rumen showed that the rates of proteolysis of fraction I in vitro was approximately 80% of the rates in sheep.

3. Using 14C uniformly-labelled fraction I protein at low concentrations, proteolysis exhibited 1st-order kinetics. Over a wide range of protein concentrations the velocity v. substrate concentration curve showed Michaelis–Menten characteristics typical of an enzyme-catalysed reaction. With rumen fluid from a hay + concentrate-fed sheep the maximum velocity was 2.6 mg protein nitrogen/1 per min and the Michaelis constant was 75 mg nitrogen/1.

4. Rapid adsorption of 14C-labelled fraction I protein onto bacterial cells preceded proteolysis.

5. Sucrose-density-gradient analysis showed initial incorporation of 14C from protein into rumen bacteria followed by partial transfer to rumen protozoa.

6. No peptides were detected during proteoiysis showing that the rate-limiting step occurred during the initial stages of proteolysis. Only small amounts of free amino acids were released except for leucine, isoleucine, valine and ornithine, which showed significantly increased levels.

7. Volatile fatty acids were the main 14C-labelied end products and were rapidly produced in descending concentrations: acetate > propionate > 3-methyl + 2-methyl butyrate > butyrate > isobutyrate > valerate.

1. Four pelleted diets were prepared containing milk or isolated soya-bean protein (ISP) as the major protein source. The milk and ISP were given either as intact proteins or partially (0·65) hydrolyzed with papain before feeding.

2. The diets were given ad lib. to thirty-two pigs from 7–28 d of age. The pigs were slaughtered at 28 d of age.

3. Weight gains, food conversion ratios and nitrogen balances of pigs given diets containing milk protein were better than those of diets containing ISP (231 g/d, 0·80 and 11·5 g/d compared to 209 g/d, 0·88 and 9·00 g/d respectively)

4. Partial hydrolysis of proteins before feeding did not affect the performance of the pigs.

5. Apparent digestibilities of N before the ileum and in the whole tract were 0·78 and 0.94 for the pigs given the ISP diets and 0·86 and 0·97 for the pigs given the milk-protein diets.

6. Retention time of ISP diets in the whole digestive tract was 1475 min and that of the milk-protein diets was 1089min.

7. pH of digesta in the stomach was 5·0–5·3 for all diets and increased to 6·9–7.1 in the ileum.

8. There were no differences in flows of total N and protein N to the ileum and lower digestive tract between the pigs given the intact- and hydrolyzed-protein diets.

9. Apparent absorptions of N in the stomach, duodenum and jejenum were greater in the pigs given diets containing hydrolyzed proteins than in those given diets containing the intact proteins.

10. Flows of total N and protein N to the ileum tract were greater when the pigs were given the ISP diets than when they were given the milk-protein diets.

11. Hydrolysis of proteins before feeding resulted in a reduced trypsin and chymotrypsin activity in the duodenum and pancreas.

12. Retention of dietary N in the carcass was greater in pigs given the milk-protein diets (0·79) than in those given the ISP diets (0·68).

1. An experiment is reported in which the effects of giving copper sulphate-supplemented diets and control unsupplemented pair-fed diets to laying hens were compared.

2. The level of food intake significantly adversely affected mean body-weight, egg number, egg weight, liver, kidney, oviduct and ovary weights. Gizzard weight/kg body-weight was significantly increased both with decreasing levels of food intake and increased CuSO4 supplementation.

3. There was evidence of a depressing effect of CuSO4per se on egg production and possibly on oviduct and ovary weight.

4. Liver lipid concentration was significantly decreased with decreasing levels of food intake and the results also suggest a depressing effect of CuSO4.

5. The Cu concentrations and total contents in liver and kidneys were significantly increased by dietary added CuSO4. Liver and kidney Zn and Fe concentrations were increased with decreasing levels of food intake rather than by CuSO4. addition.

1. The relative potencies of three lysine, one tryptophan and six methionine analogues to their corresponding L-amino acids were determined.

2. Male poults, 9 d of age, were used in five 14 d experiments. Experimental diets were formed by adding increasing levels of an amino acid (L-isomer) or its analogues to a basal diet deficient in the test amino acid. Multiple-regression analyses of body-weight gain v. level of added or amount of consumed amino acid supplement were computed. Relative potencies of the analogues were calculated using the slope-ratio technique.

3. Type of independent variable used in the regression analyses did not significantly affect relative potency values.

4. From regression analyses with level of added amino acid supplement as the independent variable, relative potencies (with 95% confidence intervals) on a molar basis of each analogue as a percentage of the respective amino acid were: hydroxymethyl-L-tryptophan monohydrate 9 (−12, 22), DL-methionine sulphone 3 (−68, 36), DL-methionine hydantoin −10 (−63, 29), L-cystine 8 (−31. 40), DL-methionine sulphoxide 59 (24, 95) and 46 (18, 74), oleoyl-DL-methionine 77 (37, 138), methionine hydroxy analogue calcium 93 (65, 128), dicocoyl-L-lysine 23 (5, 41). bis-hydroxymethyl-L-lysine-calcium 69 (54, 82) and 41 (−1, 80), mono-hydroxymethyl-L-lysine-calcium 89(77, 101) and 99(65, 134).

5. The first four analogues appeared to have little or no amino acid activity. DL-methionine sulphoxide, dicocoyl-L-lysine, and bis-hydroxymethyl-L-lysine-calcium were partially active. Relative potencies of oleoyl-DL-methionine, methionine hydroxy analogue calcium, and mono-hydroxytmethyl-L-lysine-calcium were not significantly different from those of their corresponding amino acids.

1. The results of nine estimates of the efficiency of utilization of supplements of free lysine by growing pigs fed once daily and reported by Batterham (1974) and Batterham & O'Neill (1978) were re-analysed using carcass rather than live-weight values as the criteria of response.

2. The efficiency of utilization of free lysine with once daily feeding relative to frequent feeding was 0·53 using carcass gain as the criterion of response (P < 0·001), and 0·56 using food conversion efficiency on a carcass basis (P < 0·001). These estimates were lower than estimates of 0·67 using live-weight gain (P < 0·01) and 0·77 using food conversion ratio on a live-weight basis (P < 0·05).

3. The results indicate that current estimates of the lysine requirements of pigs that are based on responses to supplements of free lysine under once daily feeding regimens may be 10–30% over-estimated, as a result of incomplete utilization of the free lysine.

1. There is controversy regarding the capacity of the cat to convert 18:2ω6 to 20:4ω6 and the ability of the essential fatty acid (EFA)-deficient cat to produce 20:3ω9.

2. This paper reports the isolation and identification of 20: 3ω9 from kidney phospholipids of EFA-deficient cats.

3. The results suggest that the cat is capable of limited synthesis of 20:4ω6 using a Δ5- and Δ8-desaturase.

1. The supply and utilisation of acetate has been estimated simultaneously in the whole animal and tissues of sheep using a combination of isotope-dilution and arteriovenous-difference techniques. Animals were made alloxandiabetic and acetate metabolism was compared when stabilized to normal metabolite levels with insulin (ITA sheep) and when food and insulin had been withdrawn for 36 h (fasted, diabetic sheep).

2. Acetate was simultaneously produced and utilized by all tissues. The exogenous (or gut) supply of acetate was the most important determinant of circulating acetate level. Endogenous acetate was produced mainly in the liver; 77 and 94% in fasted, diabetic and ITA sheep respectively. The production of endogenous acetate remained fairly constant and was not related to ketogenesis, which supports the idea that circulating acetate is largely a product of fermentation. The liver, gut and muscle utilized 17, 25 and 54% respectively (96% total) of the acetate entry rate in ITA sheep; a similar percentage utilization was found in fasted, diabetic sheep.

3. Acetate is largely oxidized to carbon dioxide in the gut and muscles of sheep and may account for 30–40% of their oxidative metabolism. This figure is similar to that for the whole animal. The total acetate taken up by the liver could account for 30% of the oxygen consumption; however, the liver may not directly oxidize all the utilized acetate.

4. The over-all conclusion from this study is that acetate is largely of dietary origin and the major factor determining its rate of utilization is the arterial concentration.

1. Both albumin and transferrin have been suggested as carriers of zinc in plasma. Their relative importance in Zn transport was therefore investigated as a preliminary to a study of the rates of passage of Zn through plasma.

2. The apparent log stability constant for Zn binding to human apotransferrin at pH 7·4 was estimated to be approximately 5·9 which is substantially lower than previous reports of 7·0 for the corresponding value for Zn binding to albumin (Giroux & Henkin, 1972).

3. When the relative abilities of human albumin and apotransferrin to compete for Zn with low-molecular-weight chelators were compared at the same relative concentrations of these proteins as are found in plasma, albumin retained substantially more Zn than transferrin.

4. It seems likely that albumin acts as the major transport protein for Zn in plasma of most species, Zn also being present firmly bound to α2-macroglobulin.

5. In porcine plasma or serum however, there were three major Zn-binding proteins, two of which were probably albumin and α2-macroglobulin. The nature of the third component remains unknown but it appeared to have a molecular weight of between 100000–140000, it was precipitated by 2·2 M-ammonium sulphate and by 150 gpolyethylene glycol/l.

6. There were no significant differences in Zn distribution in plasma of porcine blood obtained from the aorta, the posterior vena cava or from the hepatic portal vein but use of heparin as an anticoagulant altered the normal pattern of distribution of Zn in plasma.

1. The rates of transport of zinc through plasma have been investigated in normal and endotoxin-stressed pigs.

2. 65Zn added to porcine plasma in vitro rapidly equilibrated with the Zn originally present.

3. 65Zn bound to albumin and injected intravascularly into pigs rapidly equilibrated with two kinetically distinguishable pools. The first of these pools was mainly associated with the plasma but was significantly larger than the plasma volume and substantially so in Zn-deficient pigs. The second pool appeared to represent a summation of the rapidly-exchangeable Zn within the extravascular tissues.

4. In non-stressed animals, the flux of Zn from the plasma of Zn-deficient pigs was only half that in Zn-supplemented animals.

5. Administration of endotoxin reduced the plasma Zn concentration of Zn-supplemented pigs but not of Zn-deficient animals. The fractional turnover rates of Zn were not altered in either of the two pools following endotoxin.

6. At 10 h after giving endotoxin neither the Zn content of the two pools nor the flux of Zn through them differed significantly between Zn-deficient and control pigs.

7. Intravascular infusion of Zn at a rate which essentially prevented the usual depression in plasma Zn concentration following endotoxin failed to alleviate the effects of endotoxin on Zn-supplemented pigs.

8. The reduction in plasma Zn concentration following endotoxin stress appears to be a normal physiological response which is not indicative of an increased metabolic requirement for Zn.

1. A long-term experiment was made with the Rumen Simulation Technique (Rusitec), in which the fermentation of a mixed ration of hay (1Og/d) and bruised barley (5g/d) was compared with the fermentation of the same diet in the presence of 2, 10 and 50 mg monensin/d.

2. Monensin depressed the production of acetic and butyric acids, markedly increased the production of propionic acid and virtually eliminated the production of isovaleric acid. The production of methane was decreased in the presence of monensin, but this decrease could be accounted for entirely by the changes in the production of volatile fatty acids and redistribution of metabolic hydrogen.

3. The digestibility of dry matter (DM) in the rations declined in the presence of monensin. Determinations of the rates of digestion showed that the digestion of the readily-fermented food in the initial stages was not affected by monensin, but that at 24 h digestion had been inhibited by monensin. The inhibition was due entirely to its effect on the digestion of the fibrous components. Digestion of non-fibrous material was not affected.

4. The efficiency of microbial growth, expressed as g dry weight/mol ATP formed (YATP) and in terms of dm digested, tended to be increased by monensin. This however occurred only at high, non-practical doses.

5. Urease (EC 3.5.1.5) was induced by the addition of urea to the fermentation, but monensin had no effect on urease activity. Although monensin increased the activity of protease in washed suspensions, more food protein apparently escaped degradation. This may have been due to decreased deaminative activity.

6. Monensin altered the mircroscopic appearance of the fermentation fluid, and changed the activity of some enzymes in sonicated extracts, including alkaline phosphatase (EC 3.1.3.1), acetate kinase (EC 2.7.2.1) and succinate dehydrogenase (EC 1.3.9.1). These results are discussed in terms of known sensitivities of rumen microbes to monensin and their contribution to the fermentation as a whole.

1. Endogenous levels of amino acids in ileal digests were determined as the output from pigs given protein-free diets and by extrapolation to zero intake of linear regressions of ileal amino acid output v. dietary amino acid intake. The protein-free diets included 0 or 50 g cellulose/kg and extrapolations were made from two series of four diets which contained graded levels of wheat or barley as the only source of protein. Within each series, dietary fibre level (mg/g) was maintained at approximately 140 or 190 neutral-detergent fibre (NDF) respectively. Endogenous amino acid levels in faeces were also determined.

2. Endogenous amino acid output in faeces was linearly related to dietary fibre level; endogenous ileal output increased with dietary fibre up to approximately 100 mg NDF/g, after which endogenous output no longer increased.

3. The amino acid composition of endogenous ileal protein varied little among levels of output and among different experiments. The composition appears to be determined by the predominance of mucin protein, the slow absorption of some amino acids and the methods commonly used to measure output. The very high levels of proline and glycine in ileal digesta seemed characteristic only of protein-free and low-protein diets.

4. The amino acid composition of endogenous faecal protein also varied little among different estimates, but was considerably different from that of endogenous ileal protein. Furthermore, the similarity of bacterial and faecal proteins suggested that much of the endogenous faecal protein was of bacterial origin.

1. Pigs prepared with re-entrant ileal cannulas were used to determine the ileal availability of amino acids in nine cereal grains including five wheats, sorghum (Sorghum vulgare Pers.), maize, barley and Triticale.

2. The average true availability of amino acids in these grains was 0·88 but there were consistent differences in availability among amino acids. Generally, lysine and threonine were among the least available amino acids while glutamic acid and arginine were among the most available amino acids in cereal protein.

3. There was as much variation in amino acid availability within a grain species (wheat) as among the other grains.

1. Availability values for amino acids in nine cereal grains determined by faecal analyses with pigs and by the Silcock available lysine test (Roach et al. 1967) and an in vitro digestibility assay were compared with ileal availability values for the same grains determined with pigs by Taverner et al. (1981b).

2. There was a significant canonical correlation of ileal and faecal availability values. On average, apparent faecal availability of the indispensable amino acids was 4·2% greater than apparent ileal availability, but the difference was up to 12·6% for threonine. Furthermore, the difference appeared to increase as the digestibility of the grain decreased.

3. Silcock available-lysine values for the cereal grains were unrelated to the lysine truly absorbed by the pig.

4. There were close relationships of ileal protein and lysine availability values on nitrogen digestibility determined by an in vitro assay using pronase enzyme.

1. Protein digestibility and lysine availability were determined in a range of grain samples using an in vitro digestibility assay calibrated with ileal digestibility values.

2. Mean(± SE) values predicted for nitrogen digestibility were 0·92±0·011 in wheat and 0·88±0·021 in barley, and the predicted lysine availability in wheat was 0·86±0·021.

3. Chemical and physical characteristics of the grains were determined and those most closely associated with protein digestibility for wheat were the contents of hemicellulose, neutral-detergent fibre, the bulk density, and to a lesser extent, N and acid-detergent fibre contents. These relationships were used to determine prediction equations for the available lysine content of wheat.