1. Rumen contents of a fasted fistulated wether, obtained in a faunated, defaunated and refaunated period were incubated in vitro with a mixture of cellobiose and maltose, in the presence of ammonium bicarbonate and 32PO43−. Total synthesis of microbial N (Nt) was calculated from 32P incorporation and N:P determined in microbial matter. The N:P value was not affected by defaunation. Net synthesis of microbial N (Nn) was calculated from ammonia-N incorporation. An estimate of degradation of microbial N was calculated as Nt–Nn. Energetic efficiency of synthesis was calculated from the volatile fatty acids produced during incubation, as g N incorporated per kg organic matter fermented (g N/kg OMf).

2. Defaunation decreased the proportions of acetate, butyrate and methane and increased those of propionate in fermentation end-products. Fermentation rate when expressed per mg microbial N was not affected by defaunation.

3. Expressed per unit volume of rumen contents, Nn was increased by defaunation whereas Nf remained unchanged. Thus, a decrease in degradation can be calculated. Energetic efficiences of total and net synthesis were increased from 35 and 13 to 47 and 30 g N/kg OMf respectively.

4. Specific rates of both total and net synthesis of microbial N were significantly increased by defaunation whereas the specific rate of degradation was not affected.

1. In two experiments, the sites of digestion of non-ammonia nitrogen (NAN) and the amounts of urea N recycled to the rumen were measured in mature wether sheep given diets of indigenous hill herbage (Agrostis–Festuca and heather).

2. Duodenal and ileal flow values were obtained using 103Ru-phenanthroline and 51Cr-EDTA markers in animals prepared with simple (T-shaped) cannuals. Amounts of urea N recycled to the rumen were estimated from measurements of the transfer of plasma urea carbon into rumen bicarbonate and the production rate of rumen bicarbonate using 14C-labelled urea and bicarbonate respectively.

3. The flows of NAN at the duodenum and ileum were linearly related to the intake of herbage (P < 0.001). There was a net gain of non-ammonia N anterior to the duodenum on both diets (at an intake of 460 g organic matter (OM)/d, 3.7 g NAN/d on Agrostis–Festuca and 3.3 g NAN/d on heather).

4. Net digestibility of NAN entering the small intestine was within a normal range on the Agrostis–Festuca (0.58 at 460 g OM intake) diet but low on the heather diet (0.043 at 460 g OM intake).

5. It was calculated that at 460 g OM intake only 0.9 and 1.1 g/d respectively of the duodenal NAN on the Agrostis-Festuca and heather diets could have been derived from urea-N recycled to the rumen. Thus 2.8 g and 2.2 g/d had to be accounted for as non-urea endogenous NAN.

1. Wilted perennial ryegrass (Lolium perenne L. cv. Endura) was ensiled without additive or after addition of a mixture of equal volumes of formic acid (850 g/kg) and formalin (380 g formaldehyde/kg) applied at a rate of 35 g formaldehyde/kg herbage crude protein (nitrogen × 6.25). The digestion of the two silages and the effect of supplemental N as urea or urea plus soya-bean meal on the digestion of the treated silage was studied using sheep fitted with a rumen cannula and re-entrant cannulas in the proximal duodenum and distal ileum.

2. The additive markedly reduced carbohydrate fermentation and protein degradation in the silo.

3. There were no significant differences between diets in rumen pH, dilution rate, volatile fatty acid production and the molar proportions of acetate, propionate and butyrate. However, rumen ammonia levels and the apparent digestibility of organic matter (OM), gross energy (GE) and cellulose in the stomach were significantly depressed (P < 0.05) by the additive. It also reduced (P < 0.05) the extent to which the N of the silage was degraded in the rumen and, with the treated silage, more microbial N was synthesized in the rumen than food N degraded, resulting in a net gain of N between mouth and duodenum, as compared to a net loss with the untreated silage.

4. Supplementation of the treated silage with urea or urea plus soya-bean meal significantly increased (P < 0.05) the amount of food N degraded in the rumen and rumen ammonia levels but had no effect on the apparent digestibility of OM, GE and cellulose in the stomach or on the amount of microbial N reaching the duodenum.

5. The quantity of microbial amino acids entering the small intestine and the apparent digestibility of amino acids in the small intestine were similar for all four diets. However, the quantity of food amino acids reaching the small intestine was significantly higher with the three diets containing the treated silage and consequently the apparent absorption of amino acids from the small intestine was substantially higher with these diets than with the untreated silage.

1. Male broiler chickens were given a sodium chloride-deficient or NaCl-adequate diet from 7 to 21 d of age in Expt I and 28 to 56 d of age in Expt 2.

2. NaCl-deficient chickens had a markedly poorer growth and food conversion efficiency than those given the NaCl-adequate diet.

3. NaCl deficiency was associated with an increase in basal metabolic rate and increases in oxygen consumption, heat production and respiratory quotients were also noted. The glycogen content of chicken livers was also higher.

4. Measurements of acid–base balance were found to be changed in NaCl-deficient chickens. Values for pH and bicarbonate content in blood plasma were lowered.

5. NaCl deficiency increased the packed cell volume and thyroxine level in blood plasma. Sodium and chloride contents in blood were lowered.

6. Results are discussed in relation to the decreased food conversion in NaCl-deficient chickens.

1. The rumen urea concentration in gnotobiotic lambs lacking ureolytic bacteria was equal to that of blood.

2. Bacterial urease (EC 3.5.1.5.) activity in sheep fed by intraruminal and intra-abomasal infusion was inversely related to rumen ammonia concentration.

3. A model is proposed for the facilitation and control of urea flux by wall-bound ureolytic bacteria.

1. The influence of maternal hypo- or hypermagnesaemia of foetal plasma magnesium levels was studied in pregnant ewes between the 120th and the 145th day of gestation using a permanent catheter inserted in utero into the left aorta of the foetus on the 115th day of gestation.

2. In seven ewes, carrying eleven foetuses, the injection of 1 α-hydroxycholecalciferol induced a hypomagnesaemia which lasted 72 h. This had no significant effect on foetal plasma Mg levels.

3. In five ewes, carrying six foetuses, hypermagnesaemia induced by a 2 h magnesium chloride infusion had no significant effect on foetal plasma Mg levels.

4. These results provide evidence that in sheep during the last 20 d of gestation the foetal regulation of plasma Mg is independent of the maternal plasma Mg levels.

1. The amount of 3-methylhistidine (3-MeH) has been measured in eighty-eight samples of tissue taken Post-mortem from five adults.

2. The highest concentration (μmol/g fat-free dry weight) of 3-MeH was in skeletal muscle (3.31 ± 0.05); intermediate values (2–3) were found in cardiac muscle and those tissues containing smooth muscle; and low values (less than I) occurred in parenchymal tissues such as liver and kidney.

3. There was little variation between the mean 3-MeH content of striated muscles in different individuals, and no significant difference between the 3-MeH concentrations of striated muscles taken from six different sites.

4. The results suggest that it is justifiable to use values obtained from single muscles to calculate the rate of myofibrillar breakdown from urinary 3-MeH excretion.