Selenium supplementation of grazing sheep. II. Responses in plasma and erythrocyte activities of lambs and adult wethers

Abstract

The possibility that apparently healthy lambs in the low selenium region of New England in New South Wales may suffer from subclinical nutritional muscular dystrophy (NMD) was investigated. Further studies of the response in plasma activities of the seleno-enzyme, glutathione peroxidase (GSH-px), to selenium drenching were also included. Changes in the GSH-px and glutathione reductase (GR) activities of erythrocytes and plasma and in the activities of several other plasma enzymes were monitored before and after selenium treatment, by oral drench, of lambs and adult wethers maintained in the field. Similar enzyme measurements were made in adult wethers brought indoors and given a pelleted lucerne ration containing adequate selenium. Selenium treatment caused a large, rapid but transient increase in the initially low plasma GSH-px activities of the lambs. With the exception of one animal, similar changes did not occur in the wethers drenched with selenium. However, in the 14 days prior to treatment the GSH-px activities of all wethers increased and on the day of treatment activities were substantially higher than those of the lambs; increases continued in both grazing and pen-fed wethers irrespective of treatment. The selenium content/availability of the pasture grazed by the wethers was apparently higher than that grazed by the lambs and their dams and the main flock from which the wethers were selected. Plasma activities of glutamic oxalacetic transaminase, creatine phosphokinase and sorbitol dehydrogenase of both lambs and wethers fell within normal ranges at all times. These activities indicated that the lambs, despite a low selenium status prior to treatment, were not suffering from subclinical NMD and that the rapid increase in their plasma GSH-px activity following selenium treatment was not due to acute selenium toxicity and tissue damage. The response in plasma GSH-px activity appeared to depend upon the selenium status of animals at the time when selenium was administered.