Dense pellets consisting of elemental iron and selenium (9:1 by weight) labelled with 75Se were introduced into the rumen of two groups of sheep for 1 month prior to slaughter. One group was considered to be in normal selenium status, the other had grazed low selenium pastures for 2 years prior to the experiment and were shown, by analysis of blood selenium levels, to be in low selenium status. During the experimental period the pellets released 0.5-1.3 mg selenium each day; of this, about 30% was excreted in the urine and about 1 % in the expired air. Blood selenium levels rose rapidly during the first week, then more slowly, and finally leveled out at 0.18-0.34 �g/ml. Concentrations of selenium derived from the pellets were determined in various body tissues and organs at slaughter. In the course of the experiments no toxic effects were observed, and the examination of a wide variety of tissues at autopsy indicated that in no case was there excessive accumulation of selenium. The results of these experiments are discussed in relation to the use of these pellets commercially.

Lucerne (Medicago sativa L.) in which the proteins were labelled with radioactive selenium was fed to mice. The distribution of 75Se among the various organs was studied. On the basis of 75Se activity per unit wet weight, the importance of the liver and kidney as metabolic sites is confirmed, and attention is directed to the pancreas, endocrines, and the stomach wall as additional sites where selenium is present in comparable concentrations. The relative importance of the above organs is supported by the results of autoradiography; in addition, this demonstrates the high concentration of 75Se in the cell nuclei, where selenium may play a fundamental role. Radioactive selenium from labelled lucerne was found in the milk of a lactating mouse within 4 hr of it being fed. Within 24 hr approximately 20% of the selenium absorbed by the dam had been transferred to the young mice through the milk.

The activity and distribution of the selenium-containing enzyme, glutathione peroxidase, has been determined in muscle fractions in normal adult rats and sheep. Skeletal and cardiac muscle have been examined, and in both types of muscle the major proportion of the enzyme appeared in the cytosol fraction. Enzyme activity was higher in cardiac muscle than in skeletal muscle in both species, and based on total protein present in fractions, it appears that rat muscle contains more enzyme activity than sheep muscle.In tissues from lambs born to selenium-deprived ewes the levels of enzyme were significantly depressed. Two sampling periods were selected, the first when the lambs were 2-3 weeks of age and the second at slaughter when they were 10 weeks old. Muscle, plasma and erythrocyte levels of the enzyme indicated that the most sensitive measure of selenium deficiency is likely to be that of the erythrocyte enzyme level.

Merino lambs have been weaned on to two types of dystrophogenic diet, one a synthetic-type dirt with selenium-low Torula yeast supplying most of the protein, and the other a natural diet consisting solely of selenium-low hay. Lambs not supplemented with selenium developed white muscle disease within two to three months on either regimen, some of the lambs dying within that period. Selenium, given at the rate of 2 X 3 mg per week as Na2 SeO3 as an oral drench prevented the onset of muscular dystrophy. When unsupplemented animals were subjected to daily exercise consisting of one-sixth to one-third of a mile canter in a treadmill each day from weaning, muscular dystrophy was either modified or delayed. In some cases it was entirely prevented over the experimental period. As judged by creatine phosphokinase levels in blood plasma, ECG records taken throughout the experiments, and histological examination of muscle post mortem, eight out of ten lambs in the non-exercised group developed white muscle lesions, compared with two out of ten in the exercised group.

Recently evidence was offered that selenium supplied orally to lactating ewes, as Na275Se03, was partly incorporated into milk proteins as selenomethionine (Godwin, Handreck, and Fuss 1971). Previous studies, claiming similar conversion of inorganic selenium in animal tissues, have been based on the demonstration of 75Se activity in the vicinity of certain sulphur analogues during chromatographic procedures (McConnell and Wabnitz 1957; Rosenfeld 1962).