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. 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. 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.