1. Twenty Friesian steers (225 kg live weight) were fed on mid- (M) (June-July) and late- (L) (August- September) season crops of either fresh perennial ryegrass (Loliumperenne cv. Melle) (G) or white clover (Trifolium repens cv. Blanca) (C). Each of the forage diets was offered at three restricted planes of nutrition above main- tenance to compare the effect of forage species on the efficiency of energy utilization. All diets were harvested daily from swards of regrowth forage of intended equivalent digestibility.

2. Faecal and urine excretions were measured for 7 and 5 d respectively, followed by two consecutive 24 h measurements of methane, carbon dioxide and oxygen exchange in open-circuit respiration chambers.

3. The apparent digestibility of the energy in perennial ryegrass (0.759) was marginally higher (P < 0.01) than that in white clover (0.748);the mid- and late-season forages were of similar (P > 0.05)digestibilities. Metabolizable energy (ME):digestible energy (DE) in diet G (0.837) was significantly (P < 0,001) different from that in diet C (0.812). The partition of energy losses when expressed as MJ/GJ gross energy intake (GEI) indicated that energy lost as methane was not significantly different (P > 0.05) either between forages (G 62.8, C 63.4) or between seasons (M 63.2, L 63.1). Energy excretion in urine was higher for cattle fed on diet C (77.5) compared with diet G (60.5)(P < 0.001). Heat production was similar (P 0.05) between forages (G 480, C 478), but lower (P < 0.01) for L (471) compared with M(486). Energy retention (by difference) was lower (P < 0.001) for diet C (132) than G (156) and for M (138) than L (149) (P < 0.05).

4. Parallel-line analysis of unscaled ME intake (MEI) in relation to retained energy (RE; MJ/d) indicated that the efficiency of utilization (kr) was similar (P > 0.05) between perennial ryegrass (0.42) and white clover (0.46). Linear extrapolation of the values to zero energy retention indicated that maintenance requirements of ME (Em MJ/d) were 23.3 for diet G and 28.8 for diet C. The extrapolated Emwhen expressed in relation to a measured fasting heat production (FHP) of 22.8 (MJ/d) resulted in a derived efficiency of utilization of ME for maintenance (km) of 0.97 (G) and 0.79 (C), suggesting an underestimate of Em for diet G.

5. Asymptotic exponential curves (representing the law ofdiminishing returns) were fitted to the unscaled values, ME1 and RE (MJ/d), and extrapolated to zero energy retention and zero energy intake. The derived estimates of FHP (MJ/d) 18.0 (G) and 22.0 (C) were not significantly different (P > 0.05) from the observed value of 22.8 MJ/d. Using the measured FHP as additional data points, the exponential model accounted for significantly more variance (P < 0,001) compared with the linear regression method of analysis. Exponential analysis resulted in estimates of Em (MJ/d) of 29.04 for diet G and 31.80 for C. The k, for each forage was calculated, assuming linearity of response, as 0.78 (G) and 0.72 (C). The calculation of k, at fixed positions on the exponential curve related to ME1 (expressed as multiples of Em)indicated that above 1.65 Em, kt was significantly higher for C than G (P < 0.05). With increasing plane of nutrition kf declined from 0.53 to 0.29 (G) and 0.55 to 0.36 (C) over the ME1 range measured during the experiment.

1. The distribution of iron in 59Fe-labelled pigeon (Columba L.) leg and breast muscle and liver were determined by gel filtration. While the insoluble Fe was between 14 and 25% of the total Fe from the tissues, the haem-Fe represented 79.1% (breast) to 45% (liver) of the total Fe and ferritin was between 5.5% (breast) and 26.5% (liver) of the total Fe.

2. The tissue haem-Fe concentration was found to be lower than that determined by gel filtration using the method of Schricker et al. (1982) for non-haem-Fe and obtaining haem-Fe by difference.

3. A simulated in vitro digestion procedure showed significantly (P < 0.01) reduced 59Fe solubility from 59Fe-labelled pigeon meat after cooking at 90° for 30 min.

4. 59Fe absorption from whole pigeon meat and soluble extract was significantly reduced by cooking when given to Fe-replete rats. Cooking liver, however, slightly improved 59Fe absorption in Fe-replete rats.

5.59Fe absorption from the separated pigeon-meat fractions (haemoproteins, ferritin and haemosiderin) was variable but considerably lower than that from whole meat.

6. The relative distribution of Fe compounds in meat, the processing conditions they are subjected to and the protein content and composition may all influence the absorption of meat-Fe to some degree.

1. The effect of methylcobalamin inactivation by the anaesthetic gas nitrous oxide on the activity of the cobalamin-dependent methionine synthetase (5-methyltetrahydrofolate homocysteine methyltransferase; EC 2.1. I. 13) reaction, and on DNA synthesis, in the fruit bat Rousettus aegyptiucus, was examined.

2. Methionine synthetase activity in the liver of bats exposed to N2O—oxygen (50: 50, v/v) for 90 min/d averaged 32% of that of controls after 4 d of exposure and only 5% after 12–14 weeks of exposure.

3. DNA synthesis in the bone marrow, as reflected by the deoxyuridine suppression test, was unaffected by 4 d of exposure to N2O and only minimally affected after 5–10 weeks of exposure.

4. These results suggest that DNA synthesis in the fruit bat is unusually resistant to inhibition of methionine synthetase and imply the existence of a non-methylated circulating folate pool in this species.

1. Soya-bean proteins were used to replace 30 and 50% of the protein from 59Fe-labelled pigeon (Columbn L.) and chicken meat, and the solubility of the meat 59Fe in vitro and its absorption in vivo in rats in the presence and absence of soya-bean proteins were measured.

2. Replacement of part of the chicken meat by soya-bean proteins reduced 59Fe solubility from chicken meat at all stages during simulated in vitro digestion.

3. 59Fe absorption from 59Fe-labelled chicken meat when given to both Fe-replete and Fe-deficient rats was reduced in the presence of soya-bean proteins but was unaffected by the presence of casein or bovine serum albumin. 59Fe-absorption from pigeon meat in the presence of soya-bean proteins was not reduced to the same extent as that from chicken meat.

4. There was no significant effect of soya-bean proteins on 59Fe-labelled haemoglobin Fe absorption in vivo in Fe-replete rats.

5. Absorption of 59Fe from the isolated haemoproteins from chicken meat was unaffected by soya-bean proteins but 59Fe absorption from the main non-haem-Fe fractions was strongly inhibited, particularly from haemosiderin.

1. Immature, male Wistar rats were given a low-zinc semi-synthetic diet (2 mg Zn/kg) for 22–28 d. Control groups received a similar diet supplemented with 58 mg Zn/kg either ad lib., or in amounts matched to the consumption of the Zn-deficient group. There was a rapid onset of reduced food consumption and growth retardation in the Zn-depleted animals.

2. Serosal surface area of small intestines taken from Zn-deficient rats was significantly reduced compared with that of control animals. Villi, dissected from samples of proximal jejunum, were markedly smaller than those of control rats and were present in greater numbers per unit area of serosa.

3. Luminal loss of galactose from jejunal loops in situ was significantly greater in the Zn-deficient rats compared with controls when expressed in terms of unit dry weight of intestine and serosal or villous surface area. Since only a small proportion of the total galactose remained in the mucosal tissue and associated extracellular space, this loss could only be accounted for by an increased efficiency of net transepithelial transport. Differences in total galactose absorption per unit length of jejunum were not so marked.

4. This intestinal adaptation to Zn-deficiency allows the maintenance of normal, and possibly increased, rates of hexose transfer into the body of animals exhibiting severe growth retardation, reduced food utilization and abnormal glucose metabolism.

1. Nitrogen balance (NB) was determined in entire male pigs weighing 75.6 (SE 0.56) kg and given 1.43 MJ metabolizable energy (ME)/kg live weight (LW)0.75 per d of semi-synthetic liquid diets which varied in crude protein (N x 6.38):ME from 2.5 to 14.5 g/MJ. Maximum NB of 20.8 g/d was reached with diets containing at least 6.2 g protein/MJ ME.

2. The relation between energy intake and NB was then examined in pigs of comparable live weight (mean 73.8 (SE 0.39) kg) and receiving a liquid diet not limiting in protein. The diet, containing 10.0 g protein/MJ ME, was given at eight rates from 0.24 MJ ME/kg LW0.75 per d to ad lib. by approximately equal increments. Two animals were allocated to each level and two animals were fasted during the balance period.

3. The animals fed ad lib. achieved a mean intake of 1.84 MJ ME/kg LW0.75 per d. NB increased linearly as ME intake increased up to 27.6 MJ/d (1.096 MJ/kg LW0.75per d) but thereafter remained constant at 22.8 g N/d.

1. The availability of lysine in four meat meals (MMs), four meat and bone meals (MBMs) and two blood meals was determined using the slope-ratio assay with growing pigs, rats and chicks and with two chemical techniques.

2. The availability of lysine (proportion of total) in the eight MMs or MBMs ranged from 0.48 to 0.88 for pigs, from 0.49 to 0.88 for rats and from 0.68 to 0.88 for chicks. There was no apparent relation between the availability estimates for pigs, rats and chicks for the individual meals.

3. For the two blood meals, availability estimates were 1.03 and 1.13 for pigs, 0.81 and 0.80 for rats and 1.07 and 1.02 for chicks.

4. Values for the indirect and direct 1-fluoro-2, 4-dinitrobenzene-‘available’-lysineassays ranged from 0.77 to 0.88 and 0.78 to 0.93 respectively for the eight MMs and MBMs. There appeared to be no relation between these values and the pig estimates.

1. The availability of lysine for pigs, rats and chicks was determined using samples of meat and bone meal (MBM) subjected to different pressure and temperature treatments during dry-rendering processing. The relation between slope-ratio estimates and three chemical tests for estimating ‘available’ lysine was assessed.

2. The availability of lysine (proportion of total) for pigs was 0.97 in the control. Pressure (275 kPa gauge, 141°, for 30 min) in the early stage of rendering reduced availability to 0.74 and, in the late stage, to 0.46. Maintaining the final temperature at 125° for 4 h had little effect (0.84) whereas a higher temperature of 150° for 4 h reduced availability to 0.38.

3. Availability estimates for rats were lower than those of the pig, ranging from 0.88 in the control to 0.21 for the high-temperature treatment (150° for 4 h). The effects for temperature were similar to those for the pig, whereas the effect of pressure was equally detrimental in both the early and late stages (0.45 and 0.43 respectively).

4. For chicks, availability estimates were similar to those for the pig for the control (0.93) and the two temperature treatments (0.86 and 0.31 for the 125° and 150° treatments respectively). The chick was less susceptible to the effect of pressure applied to the MBM (0.78 and 0.63 for the early-and late-stage treatments respectively).

5. Values for the indirect-and direct-1-fluoro-2, 4-dinitrobenzene-(FDNB)-‘available’-lysine assays decreased from 0.86 and 0.74 to 0.57 and 0.54 for the control and 150° for 4 h treatments respectively, indicating that approximately half the reduced availability involved reactions with the ε-amino group of lysine. There was little relation between the FDNB values and lysine availability for the treatments involving changes in pressure.

6. There was little or no relation between dye-binding capacity of the meals, as assessed by the Acid Orange-12 dye-binding procedure (Hurrell et al. 1979), and lysine availability for the three species.

1. Riboflavin deficiency at two levels of severity was produced in weanling rats by feeding deficient diets for 6 weeks and using neck collars to prevent coprophagy. The severity of deficiency was monitored by growth, liver flavin levels and the activation coefficient of erythrocyte glutathione oxidoreductase (NAD(P)H) (EC 1. 6. 4. 2 ) Control groups, receiving the same diet with ample added riboflavin, were fed either ad lib., or were pair-fed with the deficient animals.

2. The hepatic flavoenzyme, methylenetetrahydrofolate reductase (NADPH) (EC 1.5.1.20), was very markedly affected by severe riboflavin deficiency and was significantly, but less markedly, affected by the intermediate level of deficiency. This reduction in activity was due primarily to the direct effect of the diminished supply of riboflavin, and occurred to only a small extent as a result of inanition, demonstrated by a moderate reduction in activity in the more severely food-restricted of the two pair-fed groups. Since the enzyme is assayed in the presence of its flavin cofactor, FAD, it clearly cannot be reactivated in vitro, as some other depleted flavoenzymes can. The discriminatory ability in distinguishing between severe and moderate riboflavin deficiency in vivo confers some potential advantages on this oxidoreductase as a possible index of riboflavin status.

3. The hepatic activity of another key folate-metabolizing enzyme, dihydrofolate reductase (EC 1.5.1.3), was not diminished by riboflavin deficiency in the present study.

4. The ratio, labelled 5-methyltetrahydrofolic acid: other labelled compounds derived from intraperitoneally injected pteroylglutamic acid in extracts of hepatic tissue was significantly reduced in the riboflavin-deficient groups, indicating the possibility of an effect of riboflavin deficiency on folate metabolism in vivo.