SOME ASPECTS OF SELENIUM METABOLISM IN NORMAL AND DYSTROPHIC SHEEP

Abstract

For two consecutive years, ewes were fed a selenium-deficient hay obtained from an area of northern Ontario where numerous losses of calves and lambs have occurred in the past from nutritional muscular dystrophy (NMD). During the first year, only 8 of 113 lambs from the selenium-depleted ewes were affected by the disorder. This is in marked contrast to previous findings that myopathy was readily produced in first-generation beef calves from dams fed low-selenium hay harvested in the same area. A high incidence and severity of muscle degeneration occurred in 4-month-old lambs born in the second year, accompanied by very low tissue selenium levels in both the ewes and lambs. Supplementation of the ewes’ diet with selenium and vitamin E during gestation was only partially effective in preventing NMD in the lambs. The selenium levels in the tissues of lambs from ewes fed dystrophogenic hay were considerably lower than in lambs born from ewes fed a hay which contained an adequate concentration of selenium. In electrocardiographic measurements, the ECG time intervals indicated no significant differences between lambs with histologically confirmed lesions and unaffected animals.Tissue distribution and excretion of selenium were studied in selenium-depleted sheep killed at various time intervals after the administration of a single oral dose of H275SeO3. Selenium was rapidly incorporated into the tissues, highest concentrations occurring in the kidneys, liver and adrenals. The element was found to be very rapidly eliminated from ewes, with over 80% of the dose excreted in the feces within 3 days and additional excretion via the urine over a subsequent 10-day period. Selenium absorbed by the ewe was found to be effectively passed on to the developing fetus. The results indicated that NMD may have developed slowly in lambs because they have a very low selenium requirement.Selenium, but not vitamin E administration, significantly elevated the blood selenium concentration of wethers fed a low-selenium, -vitamin E purified diet.