1. Young male rats were fed on a pelleted stock diet or a variety of palatable food items (‘cafeteria’ diet) and housed at 24° or 29°.

2. ‘Cafeteria’ feeding at the lower temperature stimulated energy intake, gain and expenditure, but reduced energetic efficiency such that over 70% of the excess intake was expended.

3. Housing at 29° suppressed intake and expenditure in animals on both diets, but to a greater extent in ‘cafeteria’-fed rats and energetic efficiency was greater than control values at this higher temperature.

4. The thermogenic capacity of brown fat (mitochondrial purine nucleotide binding) was increased by ‘cafeteria’ feeding, but was suppressed in animals kept at 29°.

5. The results demonstrate that diet-induced thermogenesis is inhibited by high environmental temperatures.

1. The characteristics of digestion, passage and rumen fill of three hays: early- and late-cut perennial ryegrass (Loliurn perenne cv. Endura) and white clover hay (Trifolium repens cv. Blanca and Pronitro) were studied using six rumen-cannulated sheep fed at a restricted level of intake (18 g dry matter (DM)/kg live weight (LW) per d), in a two 3 x 3 Latin square design.

2. Voluntary intake of the same diets was measured using a further six non-cannulated sheep in a similar design.

3. Rate of digestion of the three hays was measured using dacron bags and the rates of digestion of DM and neutral-detergent fibre (NDF) for clover hay were significantly (P < 0.05 and P < 0.001 respectively) faster than those for the two grass hays whose rates did not differ. Rates of passage, determined using chromium-mordanted hay, did not differ between treatments.

4. Rumen pool sizes of DM, organic matter and fibre were generally greatest for the late-cut grass hay and lowest for the clover hay, while voluntary intake was highest (P < 0.001) for the clover hay (36.6 g DM/kg LW per d) and lowest for the late-cut grass hay (24.7 g/kg LW per d).

5. The net rate of removal of indigestible fibre from the rumen appeared to vary within the day, with maximal disappearance occurring during eating, followed by a lag phase between 5 and 10 h after feeding, with a second increase in rate between 10 and 24 h post-feeding.

1.Vitamin-D-deficient pigs were fed on a phytate-phosphorus diet and treated with vitamin D, (+D) to examine the time-course of adaptative changes in plasma minerals, vitamin D metabolites, parathyroid hormone (PTH) and calcium balance and intestinal Ca-binding protein (CaBP).

2. The 5-week vitamin D repletion (25 μg cholecalciferol/kg diet) regimen restored plasma Ca, P and alkaline phosphatase (EC 3.1.3.1) to normal, decreased PTH and markedly and rapidly increased plasma 25- hydroxycholecalciferol (25-OHD, sevenfold after 4 d) and 1, 25-dihydroxycholecalciferol ( 1, 25(OH)2D3, 1.8-fold after 4 d).

3. CaBP concentrations were markedly elevated all along the digestive tract, especially in the distal regions.

4. Ca absorption and retention were enhanced (fourfold and sixfold respectively) by the +D diet.

5. The improved Ca absorption, coupled with increased CaBP and 1, 25(OH)2D3 levels, suggest that vitamin D metabolism in phytate-P-fed pigs is sensitive to the depressed Ca availability due to phytate feeding. It also indicates that CaBP may play an important role in the adaptation of Ca absorption.

6. Persistent hypercalciuria indicates that mineral metabolism was still affected by the phytate nature of the dietary P in spite of the vitamin D treatment.

1. In the previous work (Varvikko & Lindberg, 1985), 15N-labelled rapeseed (Brassica napus), barley, ryegrass (Lolium perenne) and barley straw were incubated in the rumen in nylon bags for 5, 12 and 24 h and microbial nitrogen in the residues was quantified using the feed 15N-dilution method. In the present study, residual amino acids (AA) of these feeds were analysed, and microbially corrected AA of feed origin (feed AA) were estimated as the difference between total residual AA and respective microbial AA, assuming a constant AA composition for the microbial protein.

2. In barley and barley-straw residues, and also in ryegrass incubated in the rumen for 24 h, very large enrich- ment by microbial N and AA-N was found. The microbial enrichment was rather small in rapeseed residues and ryegrass incubated for 5 or 12 h. During the rumen incubation, feed N and AA-N (g/kg feed dry matter (DM)) decreased very clearly in all the feeds, and feed and incubation time effects were always statistically significant (P < 0.001).

3. The slow degradation of essential (E) feed AA compared with the respective non-essential (NE) AA degradation increased the proportion of feed EAA (g/kg determined feed AA) in barley and barley-straw residues. In rapeseed and ryegrass, residual feed EAA: NEAA remained very similar to the original. Branched-chain (Br) AA tended to increase proportionally in all the feed residues, suggesting these AA to be, on average, more resistant against microbial degradation in the rumen than other AA. Similarly, lysine was clearly increased in barley residues. A rumen degradation faster than the average rate caused decreased residual feed glutamic acid in rapeseed; methionine, alanine and glycine in barley; arginine and alanine in ryegrass; and methionine, asparagine and tyrosine in barley straw. Feed and incubation time effects were significant (P < 0.054–001) for feed AA (g/kg determined feed AA) grouped as EAA, BrAA or NEAA, and for most individual AA, as well as for feed AA disappearance (%) and relative amounts (%) of feed AA in the respective residual AA.

4. According to present findings, AA composition of the rumen-undegraded vegetable feed residues may markedly differ, either quantitatively or qualitatively (or both), from their original AA composition. When determining the feed AA composition of nylon-bag residues, the microbial error may be very large with starchy or fibrous feeds of low protein content. The microbial AA do not, however, considerably confuse the AA determination of protein-rich feeds.

1. Eight wether sheep were offered a diet of perennial ryeigrass (Litum perenne cv. Endura) hay once daily at two levels of intake (11 and 16.5 g dry matter (DM)/kg live weight (LW)) with or without maize starch (175 g DM/kg hay DM). The experiment consisted of four periods. each lasting 32 d. Rates of digestion of the hay were measured by incubation in dacron bags and rates of passagc using chromium-mordanted hay. Rumen pool sizes of DM, organic matter and fibre were measured by emptying the rumen.

2. The inclusion of starch in the diet appeared to increase significantly (P < 0.01) the lag phase before the start of fibre digestion, as observed both in the dacron bag studies and in the slower initial disappearance of digestible neutral-detergent fibre (NDF) from the rumen recorded by emptying of rumen contents. However, there was no significant effect of starch on apparent digestibility of fibre in the whole tract.

3. The main effect of increasing the level of feeding wax, to increase the rate of passage with a consequent decrease in overall digestibility. The fractional rate of passage increased from 0.0318 to 0.0400 as the level of feeding increased, while apparent digestibility of NDF decreased from 0.755 to 0.724.

4. On all treatments the weight of indigestible fibre in the rumen remained more or less constant between 5, 10 and 15 h after feeding, but was significantly lower at 24 h. These results suggest that a high proportion of the outflow of material from the rumen not associated with feeding appears to occur during the second half of the feeding cycle.

1. Expt 1. Six 200 kg Hereford heifers fitted with rumen and abomasal cannulas were fed adlib. on alkali-treated oat straw sprayed with urea and minerals, with no supplement (O), or 700 g rolled barley (B) or cottonseed meal (C)/d, in a 3 x 3 Latin square with two replicates.

2. Intakes of the basal diet were not significantly affected by the supplements. Intakes of digestible organic matter (OM) were 3135, 3325 and 3515 g/d on diets O, Bland C respectively. Abomasal OM flow on diet C was 13 and 12% higher than on diets O and B respectively (P < 0.05) which was associated with a decrease in the proportion of OM intake apparently digested in the rumen ( P < 0.05) and an increase in the proportion of abomasal OM digested in the lower gut ( P < 0.05).

3. Total nitrogen and bacterial N flows at the abomasum were significantly higher (P < 0.01 and P < 0.05 respectively) on diet C than on diets O and B. Efficiency of bacterial N synthesis on diet C was 19 and 28% higher than on diets 0 and B respectively ( P < 0.05).

4. Dry matter (DM) pool size in the rumen was greater on diet C than on diets O and B (P < 0.05).

5. Expt 2. Thirty-three 210 kg Friesian heifers were allocated to the same treatments as in Expt I. Intakes of the basal straw diet were not significantly affected by the supplements. Intakes of digestible OM were 3.80, 4.16 and 4.34 kg/d on diets O, B and C respectively.

6. Rumen ammonia and plasma urea levels were significantly higher on diet C than on diets O and B ( P < 0.05).

7. Live-weight gains were 679, 838 and 1051 g/d on diets O, B and C respectively ( P < 0.01) and live-weight gain/MJ metabolizable energy intake was highest on diet C (P < 0.01).

8. It was concluded that the growth response to barley was attributable to the increase in energy supply, and that the additional response to cottonseed meal was attributable to greater protein absorption arising from greater abomasal flows of bacterial and dietary proteins.

1. Lean (Fa/?) and obese (fa/fa) Zucker rats were adrenalectomized or sham-operated at 19 d of age (3 d before weaning). Injection of corticosterone for 3 d after weaning (1.0 mg/d) was necessary to ensure survival of adrenalectomized fa/fa but not Fa/? rats. Intact and adrenalectomized fa/fa rats had a lower rectal temperature than Fa/? animals before and 3 d after adrenalectomy. The post-weaning survival of adrenalectomized fa/fa rats was enhanced by maintenance at an ambient temperature of 30° rather than 22°.

2. Adrenalectomized and sham-operated rats were therefore kept at 30°, fed ad-lib. and killed at 34 d. Adrenalectomy had only small effects on the growth, body composition and appetite of Fa/? rats. The hyperphagia, greater lipid content, reduced protein content and hyperinsulinaemia of fa/fa rats were completely abolished by adrenalectomy.

3. Intact fu/fa rats had higher liver glycogen contents and higher activities of the hepatic enzymes tyrosine aminotransferase (EC 2. 6. 1. 5) and acetyl CoA carboxylase (EC 6. 4. 1. 2) than intact Fa/? animals. Adrenalectomy abolished these phenotypic differences.

4. Injection of adrenalectomized rats with 1.0 mg corticosterone-21-acetate daily from weaning to 34 d restored the abnormal body composition, hyperphagia, hyperinsulinaemia, higher hepatic glycogen and enzyme activities of fa/fa rats.

5. In a second experiment adrenalectomized rats were injected with 1.0 mg corticosterone-21-acetate daily from weaning to 34 d and kept at 22°, fa/fu rats adrenalectomized and injected with corticosterone had a reduced body lipid content compared with intact fa/fa rats but still contained more lipid than intact or similarly treated Fa/? animals.

6. In both experiments adrenalectomized Fa/? and fa/fa rats injected daily with corticosterone had the same plasma concentrations of this hormone when killed 3 h after the last injection at 34 d. It is concluded that corticosterone is required for expression of the abnormal appetite, hyperinsulinaemia and body composition of the fa/fa rat.

1. The significance of blood urea-nitrogen transfer to the rumen was examined in sheep given alkali-treated wheat straw supplemented with 3.5 (diet A), 5.9 (diet B) and 11.6 (diet C) g urea-N/kg dry matter (DM).

2. Mean voluntary intakes of DM (g/d) were 897, 1149 and 1225 for diets A, B and C respectively, indicating significant (P < 0.05) intake responses to urea supplementation. Digestion studies were conducted at 90% of voluntary intake. Dietary N intakes (g/d) were 7.1, 11.5 and 18.6 for diets A, B and C respectively.

3. Absorption of ammonia-N from the rumen (g/d) was 3.5, 6.7 and 8.9 for diets A, B and C respectively, with all dietary differences being significantly different (P < 0.05).

4. Non-ammonia-N (NAN) leaving the abomasum (g/d) was 9.6, 12.7 and 14.8 for diets A, B and C respectively. Microbial N leaving the abomdsum (g/d) was 6.8, 9.6 and 10.7 for diets A, B and C respectively. Hence, significantly (P < 0.05) more N was provided to the intestines with increased urea supplementation. Net efficiencies of microbial protein synthesis (g N/kg organic matter apparently digested in the rumen), estimated from 16N incorporation, were 24.2, 23.7 and 25.3 for diets A, B and C respectively, and were not significantly different (P > 0.05).

5. Calculated proportions of microbial N derived from rumen NH2-N were 1.05, 0.95 and 0.91 for diets A, B and C respectively, reflecting the high proportion of total N as urea-N in the diets. Proportions of microbial N derived from blood urea-N were 0.31, 0.21 and 0.12 for diets A, B and C respectively, indicating a decreasing significance of blood urea as a source of microbial N as dietary urea increased (P < 0.05).

6. Transfer of blood urea-N to the rumen (g/d) was 3.8, 4.7 and 2.6 for diets A, B and C respectively, being significantly (P < 0.05) lower on diet C. Using an estimate, of the salivary contribution of urea-N to the rumen, it was concluded that there was a significant though not large transfer of blood urea-N across the rumen wall on all diets.

7. Net transfer of blood urea-N to the rumen was estimated from a two-pool model and was +0.4 g/d for diet A, though this was not significantly different from zero. Net transfers for diets B and C were -2.0 and - 6.3 g N/d respectively.

8. Significant intake responses to exogenous urea supplementation were observed because of a limited capacity to recycle N to the rumen under the conditions of low dietary N supply imposed.

1. Rumen microorganisms convert trans-aconitate to tricarballylate. The following experiments describe factors affecting the yield of tricarballylate, its absorption from the rumen into blood and its effect on mammalian citric acid cycle activity in vitro.

2. When mixed rumen microorganisms were incubated in vitro with Timothy hay (Phleum praiense L.) and 6.7 mM-trans-aconitate, 64 % of the trans-aconitate was converted to tricarballylate. Chloroform and nirate treatments inhibited methane production and increased the yield of tricarballylate to 82 and 75% respectively.

3. Sheep given gelatin capsules filled with 20 g trans-aconitate absorbed tricarballylate and the plasma concentration ranged from 0.3 to 0.5 mM 9 h after administration. Feeding an additional 40 g potassium chloride had little effect on plasma tricarballylate concentrations. Between 9 and 36 h there was a nearly linear decline in plasma tricarballylate.

4. Tricarballylate was a competitive inhibitor of the enzyme, aconitate hydratase (aconitase; EC 4.2.1.3), and the inhibitor constant, KI, was 0.52 mM. This KI value was similar to the Michaelis-Menten constant (Km) of the enzyme for citrate.

5. When liver slices from sheep were incubated with increasing concentrations of tricarballylate, [I4C]acetate oxidation decreased. However, even at relatively high concentrations (8 mM), oxidation was still greater than 80% of the maximum. Oxidation of [I4C]acetate by isolated rat liver cells was inhibited to a greater extent by tricarballylate. Concentrations as low as 0.5 mM caused a 30% inhibition of citric acid cycle activity.

1. The effects of dietary polychlorinated biphenyls (PCB) and excess tyrosine on serum and liver lipids, urinary ascorbic acid and catecholamines were compared in male Wistar rats.

2. Serum levels of cholesterol, urinary ascorbic acid, norepinephrine, epinephrine, dopamine and histamine were significantly increased in rats given either PCB or excess tyrosine.

3. The hypercholesterolaemia induced by PCB or excess tyrosine was blocked by the adrenergic α-blocker, phenoxybenzamine.

4. The present results suggest causal interrelations between the hypercholesterolaemia induced by dietary PCB or excess tyrosine and the secretion of catecholamines.

1. The objective of the present experiment was to study the level of plasma somatomedin-C (SM-C) and the status of zinc in rats as affected by three levels of Zn given in combinations with two levels of protein.

2. Six groups of rats were fed, for 21 d, on six different diets based on combinations of two levels of dietary protein (low protein, 75 g/kg; high protein, 200 g/kg) and three levels of zinc (low Zn, 0.9 pglkg; moderate Zn, 55 pg/kg; high Zn, 110 pglkg). All groups were pair-fed with the group receiving the low-Zn-low-protein diet. An additional group of six rats served as an ad lib.-fed control group and was fed on a diet that contained 55 pg Zn/kg and 200 g protein/kg ad lib.

3. Body-weight gain and food intake were recorded daily. Rats were killed at the end of the experimental period (21 d). Zn was assayed in plasma, tibia and liver by atomic absorption technique. Plasma SM-C was assayed by radioimmunoassay.

4. In rats given the low-Zn-low-protein diet, the level of plasma SM-C increased in response to the increase in the amount of Zn or Zn and protein in the diet. However, no change was observed when the level of protein alone was increased.

5. Among all groups tested, adlib.-fed rats showed the highest level of plasma SM-C. Thus it may be concluded that a balanced diet combined with adequate food intake is necessary to maintain an optimal level of plasma SM-C.

1. Iron absorption was measured in weanling riboflavin-deficient (RD) rats or weight-matched (WM) controls fed on appropriate diets for 7 weeks. Concentrations of radio-Fe (68Fe) in plasma were monitored every 30 min for 4 h following intragastric administration.

2. Total Fe absorption in RD rats was significantly lower than that in WM controls, and the tissues of the stomach and small intestine of RD rats retained significantly (P < 0.001) more 68Fe by comparison with WM groups.

3. In a separate experiment, ferritin-Fe concentrations were measured in the livers of four groups of rats (adlib. (C), pair-fed (PF) and WM controls and RD) at day 0, and subsequently at days 14, 21, 28, 35 and 49.

4. Liver ferritin-Fe concentration was significantly lower (P < 0.05) in RD rats than in all other controls after 3 weeks on the respective diets and remained lower for the remainder of the experiment.

1. The present paper reports the effects on rumen fermentation and plasma metabolites and hormones of giving fixed rations of hay and high-cereal concentrates at different meal frequencies to lactating cows. In Expt 1 the total ration was given in two and twenty-four meals daily and in Expts 2–4 the concentrates were given in two and five or six meals and the hay in two meals daily. The diets contained 600–920 g concentrates/kg.

2. In Expt I, minimum rumen pH was higher but mean pH was lower when cows were given their ration in twenty-four meals/d rather than two meals/d.

3. In all the experiments, the effects of increased meal frequency on the molar proportions of rumen volatile fatty acids (VFA) were small and not significant, although there was a general tendency for the proportion of acetic acid to increase and that of propionic acid to fall. Increasing the proportion of concentrates in the diet reduced the proportion of acetic acid and increased the proportions of propionic and n-valeric acids.

4. In Expt 3, more frequent feeding was found to reduce the concentration of non-esterified fatty acids in the blood, but changes in other metabolites were small and not significant. Increasing the proportion of concentrates in the diet reduced the concentrations of acetic acid and 3-hydroxybutyric acid and increased the concentrations of propionic acid and glucose.

5. The mean daily concentration of insulin in the blood was reduced by more frequent feeding of the higher-concentrate diet but not of the lower-concentrate diet. The concentration of glucagon also tended to fall with more frequent feeding. Increasing the proportion of concentrates in the diet increased the concentration of insulin.

6. More frequent feeding reduced the depression in milk-fat concentration caused by feeding the low-roughage diets. About three-quarters of the variation in milk-fat concentration could be related to changes in rumen VFA proportions, but the relations for the two meal frequencies had different intercepts although similar curves. The results suggest that milk-fat depression on low-roughage diets with twice-daily feeding was due to a change in rumen VFA proportions accompanied by elevated plasma insulin concentrations. The improvement in milk-fat concentration due to more frequent feeding could be explained partly by the small change in rumen VFA proportions and partly by a reduction in mean plasma insulin concentrations, but these mechanisms did not fully account for the milk-fat responses observed.

1. A low-sodium diet was given to Blackface ewes over two reproductive seasons; the diet provided 3–7 mmol Na daily, except for the period of lactation, when Na intake was increased to around 11 mmol/d. The diet of the control ewes was supplemented with sodium chloride to provide the recommended allowance of about ten times the level in the experimental low-Na diet.

2. Milk production was assessed during the first 2 months of lactation from incremental changes in the live weight of lambs during controlled sucking periods. Na and potassium were determined in milk and also in plasma, saliva and urine.

3. Neither yield nor concentration of Na and K in milk was affected by the level of Na in the diet. These results were supported by the similarity in live-weight gain of lambs in both years regardless of diet.

4. Plasma Na and K concentrations were not affected by the level of dietary Na. Na concentration in saliva and urine was significantly lower in the treated than in the control ewes, and K concentration in saliva was significantly higher.