1. In an experiment twenty-four cross-bred does were used, six in each of four physiological states: non-pregnant (NP), pregnant (P), lactating (L) or concurrently pregnant and lactating (CPL). They were offered a diet of high nutrient density (crude protein (nitrogen × 6.25) 272 g/kg dry matter (DM), metabolizable energy 15.5 MJ/kg DM) at one of two intakes on a scale based on metabolic body-weight (kg body-weight0.75). The study lasted for 24 d and was divided into three consecutive 8 d periods: ‘early’, ‘mid-’ and ‘late’ pregnancy or lactation, or concurrent pregnancy and lactation.

2. Around the mid-point of each period the does were placed for 24 h in a gradient-layer calorimeter, and measurements of energy exchange were made. N balance was also measured throughout each period of the study.

3. Milk output in L and CPL does was measured by weighing the does immediately before and after suckling once each day. Milk samples were taken from a parallel group of does and the estimates of milk composition applied to the experimental group.

4. Milk yields and composition were similar for L and CPL does in early and mid-lactation, but in late lactation the milk output from CPL does declined rapidly. This was the period of maximal fetal growth rates. Energy and N retention increased in P and CPL does in late pregnancy.

5. Regression analysis was carried out to summarize the relations between metabolizable energy intake (MEI) and energy retention (ER; MEI-heat loss) in each physiological state. The equations were:

NP: ER = 0.67 (se 0.057) MEI – 208,

P: ER = 0.67 (se 0.095) ME1 – 224,

L: ER = 0.90 (se 0.022) ME1 – 441,

CPL: ER = 0.85 (se 0.036) ME1 – 387,

where all variables are expressed in kj/kg body-weight0.75 per d.

1. A total of twenty Friesian steers were grazed on pure swards of either perennial ryegrass (Lolium perenne cv. Melle) or white clover (Trifolium repens cv. Blanca) from May to late August to examine the effect of forage species and season on nutrient digestion and supply. Within each forage species, two daily allowances of forage (i.e. 30 and 60 g dry matter (DM)/kg live weight) were given, and nutrient flow into the small intestine was measured on thirteen separate occasions (viz. seven grasses and six clovers).

2. Total nitrogen content of the grasses varied between 28 (early season), 19 (mid-) and 33 (late) g/kg DM, whilst the clovers showed a much narrower range and all values were higher (39–45 g/kg DM). In vitro organic matter (OM) digestibilities of plucked samples ranged from 742 to 809 g/kg OM (grass) and 712 to 790 g/kg OM (clover), the lowest values being noted in late June (grass) and mid-July (clover).

3. OM intakes calculated from estimated faecal OM output (using unlabelled ruthenium) and predicted OM digestibility of the consumed forage indicated mean values of 20.9 (grass) and 26.0 (clover) g/kg live weight ( P <0.001), whilst the higher forage allowances increased OM intake by approximately 8% on both grass and clover (P < 0.01) compared with the low allowance. OM intake was significantly ( P < 0.01) lower on the two primary growths of grass examined in May (mean 16.8g/kg live weight) than the other five grass diets.

4. Rumen molar propionate levels declined with season but were at all times higher on the grass than on the clover diets, whilst acetate levels were unaffected by forage species. Apart from the late-season grass, mean rumen ammonia concentration was less than 100 mg NH3-N/I on all grass diets, whilst values on the clover diets ranged from 200–350 mg/l.

5. Daily duodenal OM flows in relation to animal live weight were approximately 20% higher on the clover than on the grass diets (grass 9.2, clover 11.2 g/kg live weight, P < 0.001), but estimates of the proportion of digestible OM apparently digested in the rumen were not significantly influenced by forage species (grass 0.69, clover 0.71).

6. Non-NH3-N (NAN) flow to the small intestine varied from 0.41 to 0.76 g/kg live weight on the grass diets in response to season and forage allowance compared with values of 0.6W.94 g/kg on the clover diets, with the overall forage species effect being statistically (P < 0.001) significant (grass 0.60, clover 0.76 g/kg live weight). In relation to estimated N intakes, however, these findings revealed a considerable loss of N between mouth and duodenum on the clover diets equivalent to approximately 35% of N intake.

7. A significant regression of NAN flow/unit N intake (NI) (g/g) on N content in the forage OM (g/kg) was obtained for all forages examined: NAN/NI = 1.507–0.0185 [N/OM], residual SD 0.007, r 0.929, indicating that efficiency of utilization of the N in fresh forages in the rumen was more closely related to forage N content than forage species per se.

1. The present study was designed to compare true digestible amino acid values for meat meal with available amino acid values. True digestible values were determined with a 48 h excreta collection assay using conventional (CONV) and caecectomized (CEC) cockerels. Available values for lysine, methionine and cystine were estimated by chick growth assays.

2. True digestibilities of all sixteen measured amino acids (expressed as a proportion of the total) were lower for CEC than for CONV cockerels, with the average difference being approximately 0.10.

3. Chick growth assays based on total weight gain indicated that the availabilities of amino acids expressed as a proportion of the total amino acids in meat meal were: 0.70 for lysine, 0.75 for methionine and 0.48 for cystine. Partitioning weight gains to reflect only growth attributable to supplemental crystalline amino acid or meat meal intake consistently yielded higher availability values than when total weight gains were used.

4. True digestibility values determined with CEC cockerels were in better agreement with chick available values than were true digestibility values determined with CONV cockerels.

5. The amounts of amino acids present in the caeca of meat meal-fed CONV cockerels at 48 h after feeding were small when compared with those levels voided in the excreta and those levels consumed in the feed.

6. Multiple regression analyses of excreta and caecal amino acid profiles at 12 and 48 h after feeding suggested that significant amounts of non-digested dietary amino acids flowed into the caeca and were subsequently metabolized by the caecal microflora.

1. Three experiments were conducted to determine the flow of nitrogen through the rumen and abomasum when cows, steers and lambs were totally nourished on volatile fatty acids infused into the rumen.

2. In two dairy cows (650–700 kg) and two large steers (370–405 kg) the daily flow of non-ammonia-N (NAN) from the rumen was 50.7 and 58 mg/kg live weight (W)0.75 respectively.

3. The flows of NAN through the rumen and abomasum in four young steers (240 315 kg) were 85.0 (SE 21.0) and 195 (SE 7.0) mg/kg W0.75 respectively.

4. In the third experiment the effects of altering rumen pH and osmotic pressure on flow of NAN through the rumen and abomasum were investigated in lambs. While rumen pH and osmotic pressure influenced rumen volume and outflow they had no significant effect on NAN flow. The mean values for NAN outflow from the rumen and abomasum were 76 and 181 mg N/kg W0.75 respectively.

5. Abomasal NAN flow increased with increasing abomasal pH. When osmotic pressure was greater than about 330 mosmol/l in the rumen there was a net inflow of water, while below this value there was net loss of water.

6. For all experiments the flow of N both from the rumen and abomasum was highly variable; this has to be considered if a constant value is used for endogenous N in estimating dietary N in the abomasum.

7. With N-free infusion the rumen NHa concentration varied from 50 to 120 mg NHa-N/I.

8. The amino acid composition of rumen and abomasal N was also determined. Relative to tissue Nit contained a higher proportion of cysteine.

1. Young rats were offered to appetite a semi-synthetic diet either alone or containing the β2-selective agonist clenbuterol (4-amino-α[t-butylamino) methyl]-3, 5-dichlorobenzyl alcohol).

3. Male rats (starting weight 53 g) received clenbuterol at a daily oral dose of 200 pg/kg body-weight per d. Animals were slaughtered after 0, 4, 8, 11, 18, 21 and 25 d of treatment. At 4, 11, 21 and 25 d muscle protein synthesis was measured by the method of Garlick et al. (1980). Although clenbuterol increased the rate of protein and RNA accretion in gastrocnemius and soleus muscles, protein synthesis was not increased.

4. The results suggested that the drug had a rapid, perhaps direct, inhibitory effect on protein degradation. It is concluded that the growth-promoting effect of clenbuterol may be specific to muscle and that the drug may act in a novel manner which circumvents the physiological mechanisms responsible for the control of muscle growth.

1. Semi-synthetic diets, with dried microbial cells (Pruteen) as the nitrogen source, were used to measure N retention in 50 kg pigs given different combinations of N intake involving periods of deprivation and enhanced supply.

2. Metabolic faecal N losses were 1.92 g/d (1.26 g/kg dry matter eaten) and endogenous urinary losses were 3.96 g/d for pigs given an N intake of 6.9 g/d.

3. Compensatory N retention averaging 4.2 g extra N/d was observed in pigs given enhanced N supply by diets providing 31.0, 60.4 and 93.4 g N/d. In some instances enhanced N retention was maintained for 22 d.

4. Pigs given enhanced N supply by extravagant N intake did not maintain the compensatory response which had been evident initially.

1. The present work was undertaken to study comparatively the effect on mineral availability in rats of wheat bran and barley husk when supplying the same amount of dietary fibre (DF). The experiment involved a total of nine dietary treatments including a control group and two series of four groups with increasing amounts of fibre from the two sources (total DF ranging from 42 to 117 gsol;kg dry matter (DM)). Dietary nitrogen concentration was kept constant at 15 g N/kg DM. Zinc concentration of the diets was adjusted to the level provided by the diet with the highest wheat-bran content (21 mg/kg DM) using zinc sulphate. Other minerals were not adjusted.

2. Two experiments were performed. In Expt 1 the diets were given to 5-week-old rats during 9 d and apparent absorptions of Zn, calcium and phosphorus and the femur concentrations of Zn, Ca and P were measured. In Expt 2 the diets were given to 9-week-old rats during 12 d. Mineral concentration in femur and total and albumin-bound plasma Zn and availability of plasma Zn for enzyme reactivation were measured.

3. In the younger animals, wheat bran depressed significantly the absorption of Zn when providing 40 g DF/kg DM and absorbtion of Ca when providing 80g DF/kg DM. Barley husk depressed significantly both the absorption of Zn and Ca already at 20 g DF/kg DM. Both fibre sources had a more negative effect on Zn than on Ca absorption. Only barley husk had a small negative effect on absorption of P. Phytate did not appear as a major factor affecting mineral absorption in barley husk. All diets containing barley husk had a very low molar ratio, phytate:Zn.

4. The age orthe animals influenced the utilization of dietary minerals using femur Concentration as a criterion, particularly in the case of Zn. In the younger animals the decrease in femur Zn with fibre correlated with apparent Zn absorption both with wheat bran (R2 0.986, P < 0.01) and with barley husk (R2 0.996, P < 0.01). In the older animals femur Zn did not change significantly with fibre.

5. In the older animals, plasma Zn, albumin-bound plasma Zn and availability of plasma Zn for enzyme reactivation were lowest with the highest addition of wheat bran.

1. The fractional rate of protein synthesis (FSR) was determined in skeletal muscle, liver, rumen and cardiac muscle of wether sheep by continuous intravenous infusion of L–[4,5–3H]leucine accompanied by infusion of 0, 7.6, 15.2 or 22.8 mmol leucine/h (three sheep per treatment). FSR was calculated assuming plasma (ksp) or intracellular (ksi) leucine-specific radioactivity (SRA) was representative of the leucine precursor pool SRA for protein synthesis.

2. Plasma leucine concentration (plateau) was linearly related to leucine infusion rate, 22.8 mmol/h evoking tenfold increase in plasma concentration.

3. Difference between plasma leucine SRA and intracellular leucine SRA in all tissues diminished as plasma leucine concentration increased.

4. There were significant differences between ksi and kap estimates for liver and rumen in control sheep.

5. As leucine infusion rate increased, differences between kri and kag, diminished in all tissues. With increasing leucine infusion, in liver kst decreased and ksp was increased, in rumen kge decreased and ksp was stable, while in cardiac and skeletal muscle ksi and ksp both increased.

6. At a leucine infusion rate of 22.8 mmol/h, mean kap, and kst respectively were: rumen 1 1 (SE 2), 13 (SE 1); liver 19 (SE 2), 21 (SE 2); cardiac muscle 3–6 (SE 0.4), 3.8 (SE 0.3); skeletal muscle 4.1 (SE 0.2), 4.5 (SE 0.5) and did not differ significantly in any tissue.

1. The cortisol status (total plasma cortisol concentration, free cortisol concentration, transcortin capacity) and the characteristics of skeletal muscle binding for cortisol and dexamethasone were examined in female lambs either implanted with Zeranol or trenbolone acetate or whose dietary intake was restricted.

2. The skeletal muscle glucocorticoid receptor had a high affinity for the glucocorticoid triamcinolone (relative binding affinity 0.85) and cortisol (relative binding affinity 0.51) with virtually no affinity for trenbolone.

3. Trenbolone acetate treatment reduced the binding capacity of sheep skeletal muscle for cortisol within 2 d of implantation. The other treatments had little effect except a small reduction in the animals where food intake was restricted. Similarly, binding capacity for dexamethasone was reduced by trenbolone acetate treatment but was not affected by the other treatments. This reduction in trenbolone acetate-treated animals is, at least in part, due to a reduction in glucocorticoid receptors.

4. Transcortin capacity was elevated by Zeranol treatment but reduced with diet restriction or trenbolone treatment.

5. No support for the suggestion of free cortisol concentration being important in the growth-promoting mechanism of trenbolone or Zeranol was obtained.

6. Although insulin concentrations were not significantly altered by treatment (P > 0.05), when combining all the animals there was evidence of a negative correlation between total cortiso1: insulin vaue (P < 0.05) or free cortisol: insulin value and growth rate (P < 0.001). Free cortisol was negatively correlated to growth rate (P < 0.05) and transcortin capacity positively correlated (P < 0.01).

1. Heat production rate (H) of rumen fluid was measured in a direct calorimeter, Basal H of samples of 15 ml rumen fluid mixed with 45 ml buffer was 0.4 mW/ml rumen fluid.

2. Addition of glucose (0.4–6.4 mg/sample) was followed by a dose-dependent increase in H. Maximal H was 1.1 rnW/ml and lasted up to 5 min, returning thereafter to the basal level.

3. Expression of fermentation heat (Hf; kJ/mol substrate added) against glucose dose indicated an asymptotic dose response.

4. Maximal Hf (at infinite dilution) agreed with stoichiometric calculations whereas minimal Hf suggested a partial fermentation of the substrate at a high-glucose dose in the rumen environment.