1. The effects of a methane inhibitor, ICI 111075, and a propionate enhancer, monensin, were studied using in vitro continuous fermenters.

2. Both compounds increased the yield of substrate energy, carbon and hydrogen in volatile fatty acids (VFA). This was mainly due to an increase in the molar proportion of propionic acid.

3. Improved yields of VFA were accompanied by reductions in methane production and microbial yield.

4. Since published information showed that monensin reduced rumen dilution rate in vivo an analogous in vitro system was proposed in which a high dilution rate control fermenter was compared with a monensin treated fermenter set to run at a low dilution rate.

5.Results showed that the general intrinsic microbial activity of the chemical manipulators was not affected by changes in dilution rate. Changing dilution rate in addition to chemical treatment however resulted in substantial modifications in the net effect on the fermentation.

6. The practical implications of reducing rumen dilution rate as a side effect of chemically manipulating the rumen fermentation could involve changes in food intake, increased importance of secondary fermentations and a reduced effect of nutrients not degraded in the rumen.

1. The influence of ammonia concentration on the distribution of nitrogen derived from opaque-2 maize uniformly-labelled with 15N has been investigated during short-term in vitro incubation of bovine rumen contents.

2. Less 15N derived from maize was found in the non-protein-N (NPN) fraction during incubation without added NH3 than with added NH3, due entirely to differences in the amount of N derived from maize in the NH3 fraction.

3. From calculations based on the transfer of N derived from maize to the NPN pool and to a bacterial fraction, it was concluded that degradation of maize protein was not influenced by NH3 concentration within the examined limits.

4. The decrease in relative amount of N derived from maize in the NH3 fraction at low concentrations of NH3, together with evidence for an increased fractional turnover rate of NH3-N suggests that a deficient supply of NH3 is compensated for by increased catabolism of nitrogenous compounds derived from the rumen micro-organisms.

1. In two experiments, forty-four pigs weaned at 4–5 d of age were given diets containing milk or soya-bean proteins until slaughtered at 14, 28 or 35 d of age.

2. Additions of methionine and methionine plus lysine to the diets did not increase the proportions of these amino acids in ileal digesta.

3. In the pigs given a nitrogen-free diet, ileal digesta contained more threonine, proline and glycine than in pigs given diets containing protein.

4. The apparent and true digestibility of amino acids were greater when milk protein was fed than when soya-bean proteins were fed.

5. The apparent digestion of amino acids to the ileum of pigs given isolated soya-bean protein (ISP; Supro 610) increased with increasing age of pigs from a mean of 0.82 at 14 d of age to 0.87 at 35 d of age.

6. When milk protein was fed apparent digestibilities of methionine and lysine to the ileum were 0.912 and 0.905. The apparent digestibility of threonine to the ileum was 0.800, 0.774 and 0.504 for pigs given the milk-, ISP and soya-bean-meal (SBM)-protein diets respectively.

7. Apparent digestibilities of total essential and non-essential amino acids were 0.79 and 0.69 respectively, and true digestibilities of both were 0.82.

1. Six adult Friesian cows were given 75Se as either 75SeO32− or 75SeO42− intravenously. Five of the cows had cannulas in an hepatic vein, the portal vein and one carotid artery to enable the uptake of 75Se by the liver to be measured. Radioactive balance studies were carried out on two of the cows given 75SeO32− and two given 75SeO42−. A seventh cow was given an oral dose of 75Se-labelled barley and the excretion of 75Se in faeces, urine and milk was measured for 14 d.

2. After the injection of 75SeO32− plasma 75Se concentration decreased during the first 30 min with a mean half-life (t½) of 15.6 min. From 30 to 60 min after dosing the concentration of radioactivity increased to reach approximately 50% of the level present 2 min after dosing. Following the injection of 75SeO42− the 75Se was cleared with a mean t½ of 28.5 min during the first 30 min and plasma radioactivity increased only slightly during the next 30 min.

3. During the phase of rapid clearance of 75Se after the injection of 75SeO32− the hepatic venous 75Se concentration was approximately 5% lower than portal veous 75Se concentration. During the period when plasma 75Se activity was increasing the activity in hepatic venous plasma was 3% greater than portal activity. Of the 75Se cleared from plasma after injecting 75SeO32− 40% was calculated to be removed by the liver.

4. After intravenous dosing with 75SeO32− or 75SeO42− approximately 9.5 and 17.0% respectively of the dose injected was excreted in faeces and 10% in urine within 14 d. Almost three times as much 75Se was excreted in urine and 3.5 times as much in faeces during the first 24 h after dosing with 75SeO42− as after 75SeO32−.

1. Studies were conducted to measure the influence of perinatal undernutrition of twin-bearing ewes on ewe milk yields and lamb performance in early lactation. Comparative studies were conducted with lambs to measure the effects of postnatal nutrition on lamb performance and carcass composition. The major objective of this work was to determine the extent of the influence of postnatal nutritional deprivation of lambs.

2. From 8 weeks prepartum to 4 weeks postpartum each of forty twin-bearing ewes was given daily 0.30 MJ of ME/kg body-weight (W)0.75. Measurements were made of ewe body-weight changes, milk yields during the first 4 weeks of lactation, and of lamb performance.

3. There were three postnatal experiments with lambs of ‘light’ and ‘normal’ birth weights, wcaned from the ewes at 72 h. One hundred and four lambs were used and they were individually reared on separate allowances of lamb milk-substitute for 8 weeks. They were subsequently given a lamb concentrate ration. In Expts 1 and 2 the lamb concentrate was fed ad lib. to ‘slaughter’ live weight. In Expt 3 the concentrate was restricted for 8 weeks post weaning and then fed ad lib. A carcass analysis (bone, muscle, fat content) was conducted on all lambs after slaughter. In the first experiment, half the lambs were slaughtered at 8 weeks of age on being weaned off the milk substitute, and a carcass analysis was carried out.

4. The mean net body-weight loss per ewe from commencement of late pregnancy to 28 d post partum was 23.8 kg. The over-all mean daily milk yield was 843 g/d. The mean growth rate of the lambs was 97 g/d during the 4-week measurement of ewe milk yields.

5. Live weight gain of lambs subjected to restricted milk-substitute allowance (125 g/dry matter (DM) per d) was low, irrespective of lamb birth weight. The average daily gain over the 8-week postnatal period was 86.5 g/d on restricted milk allowance compared with 244 g/d for those fed ad lib. Conversely, the food intake and growth rate of these lambs were almost identical during feeding on ad lib. concentrates. This clearly reflected a response to compensatory food intake which was independent of either birth weight or postnatal milk allowance. The average daily gain of lambs, before weaning, on the restricted milk allowance was very similar to that of the lambs being suckled by ewes subjected to perinatal undernutrition. The effects of postnatal undernutrition of lambs was particularly reflected in the time required to reach ‘slaughter’ live weight. The period of time varied from 117 d for those on ad lib. food intake to 169 d for lambs on restricted food intake.

6. The major effect of postnatal undernutrition on carcass composition was evident in the lambs slaughtered at 8 weeks in Expt 1. The percentage carcass fat was 4.7 for those on the low milk allowance. The carcass composition of all lambs at ‘slaughter’ live weight was similar. It would appear that lambs on a restricted milk intake before weaning deposited more fat during the subsequent period of compensatory food intake.

7. It is evident from the present results that postnatal growth retardation in lambs reflects either perinatal undernutrition of twin-bearing ewes, or postnatal undernutrition of the lambs due to inadequate milk availability from the dam.

1. In two separate experiments, forty-two pigs weaned at 4–5 d of age were given diets containing milk or soya-bean protein and slaughtered at 7, 28 or 35 d of age.

2. The amino acid composition of the empty body of the pigs did not vary with age or sources of protein fed.

3. The nitrogen and amino acid contents of the empty body gain were calculated between 7 and 28, and 7 and 35 d of age. The retention of absorbed N was greater in pigs given a soya-bean meal (SBM) diet than in pigs given milk or isolated soya-bean protein (ISP) diets.

4. The retention of total absorbed N was greater in pigs given a pelleted milk diet (0.72) than in pigs given a liquid milk diet (0.58).

5. Methionine and threonine appeared to be the first two limiting amino acids, as indicated by their high incorporation into the empty body, for pigs given soya-bean proteins in Expt 3, while methionine and lysine were the first two limiting amino acids for pigs given ISP in Expt 4.

6. The addition of methionine to diets in Expt 3 reduced the retention of absorbed methionine in the empty body by 43–76%. Lysine supplementation did not alter the retention of the absorbed lysine.

7. Retention of arginine, proline and glycine in the body was greater than the apparent absorption of each of these amino acids.

1. In a randomized block design, four sheep were given 800 g daily of diets containing: chopped lucerne (L), chopped lucerne–rolled barley (2:1; LB), rolled barley–chopped lucerne (2:1; BL), rolled barley (B); each diet was supplemented with minerals, vitamins and urea as considered necessary. Chromic oxide was included in the diets as a flow marker.

2. Flows of organic matter (OM) and non-ammonia-nitrogen (NAN) to the small intestine (SI) were measured and microbial protein was identified by a 35S-incorporation procedure.

3. OM disappearance in the rumen increased linearly with increasing inclusion of barley in the diet but there was no significant change in microbial NAN flow to the SI so that the yield of microbial NAN (g)/kg fermented OM (FOM) decreased from 29.6 (diet L) to 22.7 (diet B). Changes in the energetic efficiency of microbial protein synthesis appeared to be unrelated to alterations in rumen fluid volatile fatty acid (VFA) proportions or in rumen fluid dilution rate (D).

4. The degradability of dietary protein (non-urea-N), estimated using the 35S procedure, was 0.72, 0.76, 0.86 and 0.86 for diets L, LB, BL and B respectively. Similar values were obtained from concurrent polyester-bag experiments when the fractional outflow rate of undergraded protein from the rumen (k) was assumed to be 0.046.

1. Levels of zinc in liver and plasma of the Zn-depleted rats fluctuated with the feeding cycle and were significantly higher at the bottom than at the top of the cycle. As Zn deficiency became more severe fluctuations in plasma Zn diminished. Concentrations of Zn in liver, in contrast to levels in plasma and femur, were not markedly lowered by day 15.

2. In contrast to udlib.-fed (AL) and overnight-fasted (OF) controls, some pair-fed (PF) controls had elevated levels of Zn in liver and plasma.

3. Intakes of water and food were sigdicantly correlated in Zn-deficient rats. Packed cell volumes were significantly higher for Zn-depleted than for AL and PF rats.

4. Food intakes and plasma glucose concentrations were related in AL, OF and PF control rats but not in Zn-deficient rats.

5. At day 15 of Zn deficiency the order of total plasma amino acid concentrations in the groups of rats was AL > Zn-deficient > OF > PF. Many of the differences between the AL and OF groups for individual plasma amino acids also appeared in the Zn-deficient group at the top and bottom of the feeding cycle. Differences in individual amino acid conmntrations at the top and bottom of the feeding cycle tended to be opposite in the PF and the Zn-ddicient group. Levels of tyrosine and tryptophan in plasma were correlated (P ≶ 0.05) with the cyclic feeding pattern of the Zn-deficient group; however, the ratios tryptophan or tyrosine: sum of other large neutral amino acids did not correlate significantly with the eating habits of Zndeficient rats.

1. Ten castrated young adult sheep were brought indoors and given lucerne chaff (four animals with a phosphorus intake of 2.40 g/d) and fresh Ruanui ryegrass (six animals with a P intake of 3.72 g/d) to determine various kinetic indices of their P metabolism.

2. The results obtained from combined nutritional balance and 32P radioactivity measurements were analysed using the simulation, analysis and modelling computer (SAAM) program. Since the plasma P specific activity curve was described by at least four exponential terms, a four compartmental model (M1, M2, M3 and M4) was used to describe the experimental values.

3. The mean mass of the total exchangeable P pool (MT) for the lucerne chaff-fed and Ruanui ryegrass-fed sheep was 25.5 and 28.8 g respectively, while the total P transport (VT) to the exchangeable pool (MT) was markedly lower for sheep given lucerne chaff compared to those given Ruanui ryegrass (54.1 v. 111.3 mg/kg body-weight per d). Likewise the rate of P absorption (Va), faecal endogenous loss of P (Vf), urinary P excretion (Vu) as well as the movement of P to (Vo+) and from (Vo−) the skeleton and soft tissue was also lower in the lucerne chaff-fed sheep.

4. The availability of P, that is the proportion of ingested P which is absorbed, was 0.56 and 0.62 for the sheep given chaff and fresh herbage respectively.

5. The P metabolism of one sheep (sheep no. 30) differed from the other sheep in that its plasma inorganic P concentration was higher (95 v. 54 mg/l). This was associated with a larger first compartment (M1), a more rapid P transport between M1 and M2, an increase in (Va) and a marked increase in (Vu).

1. Rainbow trout (Salmo gairdneri) of mean initial weight 35 g were given one of five experimental diets for 20 weeks. The diets contained (g/kg dry diet) 15 calcium, 10 phosphorus and graded levels of magnesium from 0.04 (diet no. 1) to 1.0 (diet no. 5). In a second experiment rainbow trout of mean initial weight 16 g were given one of six experimental diets for 20 weeks. The diets contained (g/kg dry diet): Ca (40), P (30) and levels of Mg from 0.06 (diet no. 6) to 2.0 (diet no. 11).

2. In both experiments weight gains were lowest in those trout given diets containing the basal levels of Mg (diet no. 1 and diet no. 6) but increased with increasing dietary Mg concentration. In neither experiment was there any further increase in weight gain once the Mg concentration reached 0.25–0.5 g/kg dry diet; weight gain reached a plateau at this dietary Mg level.

3. The following trends occurred in serum electrolyte concentrations as dietary Mg increased. Mg increased in both experiments, in Expt 2 it reached a maximum of 1 mmol/l when the diet containted 0.5 g Mg/kg and did not increase further; sodium was positively correlated in both experiments; potassium decreased and in Expt 2 reached a plateau minimum of 1.7 mmol/l at a dietary Mg concentration of 0.5 g/kg; Ca and P altered little in either experiment.

4. In both experiments renal Ca concentrations were greatly increased in trout given diets lacking supplementary Mg; they fell to low levels (3–5 mmol/kg) when diets conained 0.15 g Mg/kg or more. Renal K and P concentrations were negatively correlated with dietary Mg in Expt 2; other electrolytes measured were not altered in concentration by the treatments used.

5. Extracellular fluid volume (ECFV) of muscle was negatively correlated with dietary Mg. In Expt 2 it reached a minimal or normal value at 0.5 g Mg/kg diet and did not decease further. Muscle Mg concentration increased with diet Mg in both experiments and muscle K concentration was also correlated with diet Mg in Expt 2. These changes were related to the shift in muscle water. In Expt 1, P concentration was decreased with increasing diet Mg but in Expt 2 its concentration increased, these changes may have been connected with the three-fold difference in dietary P in the two experiments.

6. By contrast with skeletal muscle, Mg levels in cardiac muscle increased at low dietary Mg intakes.

7. Concentrations of electrolytes in liver did not alter with dietary treatments used.

8. The results show that Mg requirement of rainbow trout is met by a diet containing 0.5 g Mg/kg diet.

1. The maximum capacity of the bovine liver to excrete manganese in bile was determined in three Friesian-cross steers surgically prepared to allow bile flow-rate to be measured and samples collected. Plasma Mn concentrations were increased by infusing manganese chloride solutions into a jugular vein and the biliary excretion rates of Mn, copper, zinc and iron were measured.

2. The maximum capacity of the liver to excrete Mn in bile was exceeded at an infusion rate of approximately 4000 μg Mn/min, and at this rate there was a significant decrease in the concentration of Cu, Fe and Zn in bile. The maximum concentration (mean ± SE) of Mn in bile was 193 ± 19 μg/ml, and the maximum excretion rate (mean ± SE) was 1210 ± 130 μg/min for the three animals. There was no reduction in bile flow or evidence of liver damage as a result of the infusions.

1. Changes in the concentrations of the minor constituents of goat's milk were observed during 48 h starvation and on refeeding.

2. The concentrations of hexose phosphate and UDP-hexoses increased during starvation and decreased on refeeding.

3. The concentrations of phosphoenolpyruvate and glycerate 3-phosphate decreased during starvation and increased on refeeding.

4. Isocitrate: 2-oxoglutarate increased during starvation and decreased on refeeding.

5. Changes in the minor constituents of milk can be explained in terms of the metabolic changes occurring in the mammary gland during starvation. It is proposed that changes in the concentrations of these metabolites in milk reflect changes in their concentrations in the cytosol or Golgi vesicles of the mammary gland.

1. The effects of dietary supplements of ω 3 polyunsaturated fatty acids on the fatty acid composition of platelets and plasma choline phosphoglycerides were studied in vegans and in omnivores.

2. A supplement of 18:3ω3 led to an increase in 20:5 ω3 but was less effective than one of 20:5ω3+22:6ω3.

1. Measurements were made of the hepatic concentrations and contents of total and thionein-bound zinc and copper in late foetal and newborn rats and of the distribution of these metals between the particulate and soluble components of the liver.

2. The decrease in the hepatic concentration of thionein-bound Zn, which occurred with age after birth, was proportional to the increase in liver weight until the 16th day post partum; thereafter it was greater.

3. Throughout the period from birth to 25 d of age the Zn concentration remained constant in the cytosolic non-thionein fraction (i.e. total cytoplasmic Zn – thionein-bound Zn). but decreased in other compartments of the liver.

4. The same constant concentration of cytoplasmic non-thionein-bound Zn also was observed in animals with reduced total hepatic Zn contents, but normal body-weights, and in 20-d-old Zn-deficient pups.

5. The concentration of thionein-bound Cu exhibited two maxima, one at 2 d of age and the second at 14 d.

6. The total hepatic content of Cu increased significantly only between the 6th and 14th day post partum. The age-related variations in Cu contents of the particulate components closely paralleled those in the whole liver, whereas the Cu contents of the cytosolic thionein and non-thionein fractions did not increase appreciably until after the 10th day.

7. It is concluded that the cytosolic non-thionein fraction of newborn rat liver may contain particularly important metabolic sites that require Zn and a major function of Zn-thionein is to regulate is to regulate the supply of the metal to these sites. As, from birth to 26 d of age, the sum of the concentrations of thionein-bound Zn and Cu was correlated with whole liver Zn, the accumulation of Cu as a soluble metallothionein seems to be a secondary event, dependent on the hepatic Zn concentration.

1. A method for gas-liquid chromatographic analysis of the dimethyl esters of a homologous series of diabolic acids is described.

2. Only when combined with low-resolution mass spectrometry could the method be used to show unequivocally the existence of diabolic acids in natural products.

3. Diabolic acids occurred naturally in rumen and faecal lipids of all ruminants examined but could not be detected in a number of ruminant tissue samples.

4. Infused 14C-labelled (C16:0)2 diabolic acid was poorly absorbed by both simple-stomached and ruminant animals. Oxidation was more extensive in the ruminant, but there was no evidence of deposition of diabolic acid in the tissues of either animal.

1. The concentration of copper in the rat intestine was found to increase rapidly after birth to a maximum greater than 140 μg/g wet weight at 2 d of age and then to decline, at first slowly to 90 μg/g wet weight on day thirteen and then rapidly to 40 μg/g and 3.4 μg/g wet weight on the 15th and 19th day respectively. The intestinal concentration of Zn, which doubled between 1 d prepartum and 2 d post partum, also fell slowly until 10 d of age, but thereafter remained constant.

2. From the 2nd to the 15th day post partum approximately 60% of the total Cu and 50% of the total zinc in the intestine was located in the soluble fraction of the tissue. Most of the Zn in this fraction was bound by proteins of molecular weights greater than 13700 daltons, whereas most of the Cu was present as an extremely polydisperse complex of lower molecular weight. This complex in the intestine of the 5-d-old rat, in contrast with the soluble proteins of higher molecular weight. This complex in the intestine of the 5-d-old rat, in contrast with the soluble proteins of higher molecular weight, did not incorporate either 3H or 35S within 4 h of the administration of L-[4,5-3]leucine and L-[35S]cystine.

3. The loss of Cu from the intestine between the 13th and 15th day of post-natal age occurred mainly from this complex and was accompanied by the transient appearance of Cu in a fraction of low molecular weight.

4. At 21 d of age the soluble fraction of the intestine contained only a small amount of Cu. This was distributed between two protein fractions, one of which contained Zn and appeared to be a metallothionein.

5. The results are discussed in relation to the control of Zn and Cu absorption.

1. The availability of lysine in seven vegetable protein concentrates was determined using the slope-ratio assay with growing pigs and rats and with two chemical techniques.

2. With pigs, estimates of availability were lower using carcass compared to live-weight values, but there was no consistent effect of including food intake in the criterion of response. Availability estimates, using food conversion efficiency on a carcass basis were (proportion of total) linseed meal − 0·23, lupin-seed meal 0.74, rapeseed meal no. 1 0.97, no. 2 0.77, sunflower meal no. 1 0.59, no. 2 0.66, no. 3 0.54.

3. Availability estimates for lysine with rats were also lower using carcass compared to live-weight values. Estimates based on food conversion efficiency were higher than those based on weight gain. Availability estimates in lupin-seed meal and sunflower meals were in general agreement with the pig estimates, whilst that with linseed meal was considerably higher (0·82). Assays were not conducted with rapessed meal due to problems of food rejection with this meal.

4. The differences in available lysine were not detected by the chemical Silcock available-lysine test (Roach et al. 1967) nor by the direct fluoro-dinitrobenzene procedure (Carpenter, 1960).

1. The digestibilities of microbial and food proteins in the small intestine were studied in three sheep fitted with re-entrant cannulas in the proximal duodenum and terminal ileum.

2. The quantities of microbial and food proteins at the small intestine were varied by infusion of a microbial isolate or by dietary manipulation and the balance of amino acids along the small intestine was determined.

3. A mean value of 0.69 for the apparent digestibility and 0.86 for the true digestibility of total amino acids was obtained.

4. From the composition of digesta at the duodenum the daily flows of microbial and food proteins were estimated. Their true digestibilities in the small intestine were calculated by regression and found to be: microbial protein 0.87 and food protein 0.82. The mean endogenous loss of amino acids secreted into the small intestine was estimated to be 13.3 g/d.