1. Three series of nitrogen balance experiments were performed with growing rats to test the effect of amino acid imbalance on protein utilization. In Expt 1 egg protein was fed as a basal diet and supplemented with one amino acid at a time in the amounts originally found in egg protein. In Expt 2 the procedure was repeated with a barley diet, and in Expt 3 egg and potato proteins were fed together in various combinations.

2. Doubling the single amino acids, especially arginine, in an egg-protein diet reduced biological value (BV) markedly. Also the branched-chain and the basic amino acids reduced BV significantly. In the barley-based diets negative effects were also observed when the concentration of the single amino acid was doubled. However, it was assumed that the observed deleterious effects of amino acid excess were partly due to an exaggerated lysine deficiency in the barley protein when non-limiting amino acids were added.

3. The results with various combinations of egg and potato proteins showed that as potato protein was increased true protein digestibility decreased linearly, whereas BV decreased Curvilinearly. Maximum protein utilization was obtained with egg protein alone.

1. The recoveries of radioactivity in cattle urine following the intravenous administration of Nτ-[14CH3]methyl histidine were essentially quantitative in 5–7 d in non-lactating cows, bulls and steers and did not change with age.

2. The Nτ-methyl histidine was excreted unchanged in urine.

3. Nτ-methyl histidine occurred in muscle extracts both in the free form and as a perchloric acid-soluble, acid-labile form which accounted for approximately 85% of the total non-protein-bound Nτ-methyl histidine in muscle and appeared identical to a similar component identified in muscle extracts of sheep and pigs.

4. There was probably an age-related decrease in the concentration of the acid-labile component in muscle but which did not produce a measurable change in recovery of radioactivity in urine.

5. The daily excretion of Nτ-methyl histidine (E, μmol) by male cattle was highly correlated with live weight (W, kg) by the equation: <m:math><m:mrow><m:mtext>E</m:mtext><m:mo>=</m:mo><m:mn>50</m:mn><m:mo>⋅</m:mo><m:mn>4</m:mn><m:mo>+</m:mo><m:mn>3</m:mn><m:mo>⋅</m:mo><m:mn>536</m:mn><m:mo stretchy=“false”>(</m:mo><m:mo>±</m:mo><m:mn>0</m:mn><m:mo>⋅</m:mo><m:mn>044</m:mn><m:mo stretchy=“false”>)</m:mo><m:mtext>W</m:mtext><m:mspace width=“1”/><m:mo stretchy=“false”>(</m:mo><m:mi>r</m:mi><m:mspace width=“0.3”/><m:mn>0</m:mn><m:mo>⋅</m:mo><m:mn>997</m:mn><m:mo stretchy=“false”>)</m:mo><m:mo>.</m:mo></m:mrow></m:math> The excretions progressively decreased from 4.04 μmol/d per kg at 100 kg weight to 3.62 μmol/d per kg at 600 kg.

6. By the criterion of the rate of clearance of labelled Nτ-methyl histidine from the body, the excretion of Nτ-methyl histidine in urine appears to be a valid index of muscle protein breakdown in cattle.

1. The validity of the urinary excretion of Nτ-methyl histidine (Nτ-MH) by pigs as an index of muscle protein breakdown in vivo was tested using the criterion of the rate of recovery of radioactivity in urine following an intravenous dose of Nτ-[14CH3]methyl histidine.

2. Urinary recoveries of radioactivity from five animals were less than 21% of dose in 7 d after which the daily recovery was less than 0.3% per day.

3. The incomplete recoveries of radioactivity were associated with the presence in muscle of a large. pool of non-protein-bound Nτ-MH, the concentration of which increased with age.

4. The Nτ-MH in this pool was present as free Nτ-MH and in a dipeptide which constituted more than 90% of the total non-protein-bound Nτ-MH. The contribution of the peptide increased with age, reaching 99.8% in older animals.

5. The pool of non-protein-bound Nτ-MH was maintained and increased in both established and newly accreted tissue by retention of some of the Nτ-MH released by muscle protein breakdown, only a proportion of which was therefore available for excretion. Hence, the urinary excretion of Nτ-MH is not a valid index of muscle protein breakdown in pig.

1. Sheep given ground and pelleted lucerne hay (Medicago sativa) ad lib. were infused intravenously with pentagastrin, secretin, cholecystokinin (CCK) and its analogues to assess their effects on motility of the reticulo-rumen and on food intake. In the latter experiments the animals were deprived of their diet for periods of up to 6 h to induce hunger and the infusions were made before and during 3–10 min periods of feeding.

2. Pentagastrin, an analogue of gastrin, depressed intake by 35–50% (P < 0.05) when it was infused at 9 μg/kg per h during 30 min of feeding. The threshold may however be below 1 μg/kg per h as this dose decreased intake of 12–17%. The frequency of reticular contractions decreased by 13, 35, 39 and 44% when 1, 3, 9 and 27 μg pentagastrin/kg per h respectively was infused (P > 0.025).

3. Secretin depressed food intake 38% after 30 min (P > 0.025) when 8 Clinical Units (CU)/kg per h was infused but the threshold could be less than this dose since 0.5 CU/kg per h depressed intake by 12%. Contraction amplitude but not frequency decreased at 8 CU/kg per h.

4. CCK produced a 39% decrease in intake during the first 10 min of feeding (P < 0.05) and the threshold was between 5 and 15 Ivy Dog Units (IDU) or 425 and 1276 pmol/kg per h. The frequency of reticular contractions was not affected by 1.7 IDU/kg per h but it was depressed 21 and 63% by 5 and 15 IDU/kg per h. Octapeptide at 1.5 and 3 μg (1312 and 2624 pmol)/kg per h depressed intake by 11 and 43% respectively after 10 min (not significant) and 1.5 μg/kg per h depressed motility by 39% (P < 0.01). Ceruletide at 810 ng (599 pmol)/kg per h depressed intake by 31% (not significant) after 10 min and decreased motility by 52% (P > 0.05). The threshold dose for ceruletide on intake appeared to be about 90 ng or 66 pmol/kg per h which is considerably less than that for CCK or octapeptide.

5. The biological significance of gastrointestinal hormones as signals of satiety in normal sheep is not known since doses of pentagastrin and CCK that suppressed intake also interfered quite markedly with motility. However there is good reason to suspect that elevated concentrations of gastrin and CCK in blood of parasitized sheep may account at least in part for their symptoms of rumen atony and reduced food intakes.

1. Distribution of copper and molybdenum was followed in the body tissues of sheep fed on high levels of Cu (82 mg Cu/sheep per d), sulphur (3·77 g S/sheep per d) and different levels of Mo (0·6 20·8, 38.4 and 58.5 mg Mo/sheep per d).

2. Liver Cu content decreased as Mo intake increased from 0.6 to 38.4 mg/d, but increased again at high intakes of Mo. With an Mo intake of 58.5 mg/d, the Cu content of liver, kidney, lung, spleen and muscle tissue was significantly higher than with an intake of 20.8 mg Mo/d. The trend of increased Cu concentrations in kidneys and plasma was already evident at an Mo intake of 38.4 mg/sheep per d.

3. High positive correlations were observed between Cu and Mo in both the kidney cortex and medulla of the sheep at the two highest Mo treatments.

4. At constant S intake, Mo concentrations in the tissues tended to increase in proportion to Mo intakes. No indication of any detrimental effect due to the accumulation of Mo in the tissues was observed.

5. It was suggested that in the presence of an abundance of Mo, Cu and S, compounds containing these minerals in metabolically unavailable forms accumulate in the body, first in the kidneys, but eventually also in the other tissues of the sheep.

1. The effects of incorporation of copper sulphate supplying 250 mg copper/kg semi-purified diet with graded amounts of calcium pantothenate (CaPa) were studied in chicks.

2. When the doses of CaPa were marginally adequate or less the Cu supplementation induced severe signs of pantothenic acid (PaA) deficiency.

3. Livers of the Cu-treated birds given low doses of PaA had lower concentrations of total and bound PaA than those of the corresponding control birds. The bound:total PaA value was also reduced.

4. The amount and concentration of coenzyme A (CoA) were significantly less in the livers of Cu-treated chicks. Fatty acid synthetase activity was not reduced.

5. It is suggested that high dietary supplements of CuSO4, induce PaA deficiency through interference in the biosynthesis of CoA.

1. Serum thymic hormone was assayed in genetically-obese (C57B1/6J ob/ob) mice and lean controls (+/+, +/−) of the same strain.

2. The thymic hormone activity was higher in the majority of the obese animals compared with non-obese mice.

3. The number of antibody-forming cells in the spleen expressed as a proportion of the total mononuclear cells was increased in the obese mice.

4. It is suggested that obesity is associated with significant changes in the thymic hormone levels which may alter the relative proportion of lymphocyte subsets and cell-mediated immunity.

1. The responses of germ-free (GF) and conventional (CV) chicks to suboptimal amounts of dietary calcium pantothenate (CaPa) were compared. At the lower levels of supplementation the signs of deficiency were more severe in the CV chicks.

2. Calculations based on mean body-weibts of chicksgiven graded dietary supplements of calcium pantothenate (CaPa) in both environments showed that, to achieve the same body-weight and freedom from signs of deficiency, the GF birds required only approximately two-thirds the amount of CaPa as was needed by corresponding CV birds.

3. Increasing the dietary supplement of CaPa resulted in increased contents of PaA in the livers. GF birds had more PaA per liver than their CV counterparts. In both instances the effect was due to the larger liver size. Concentration of PaA in the liver was not al€ected by dietary supplement nor by the environment.

4. CV birds were deemed to be under greater stress than GF birds because their adrenal glands were heavier and contained less cholesterol.

5. CV chicks deliberately stressed by injections of adrenocorticotrophic hormone had heavier adrenals with lower cholesterol contents than unstressed controls, but the condition was not altered by increasing the dietary supply of CaPa.