Intake of selenium and other nutrients in relation to selenium status and productivity of grazing sheep

Abstract

The selenium status of the sheep and seasonal fluctuations in the intake of dry matter, digestible dry matter and selenium over a 12-month period were measured in an experiment with 80 ewes and their offspring on annual pasture in the south-west of Western Australia. Forty of the ewes received an intraruminal selenium pellet 1 month prior to lambing in June. At weaning half of the lambs born to ewes in each treatment also received an intraruminal selenium pellet. There was a distinct seasonal pattern in the quality and quantity of pasture ingested. Dry matter digestibility was highest in winter (68.9%), declined during spring and was lowest during summer (32.3 %) when intake of digestible dry matter was not sufficient to maintain the liveweight of weaner sheep. Selenium intake by ewes was highest in winter (64 ¦g/day), when dry matter (DM) intake was maximum (1348 g/day). The intake of selenium (31 ¦g/day) and the plasma selenium concentration (7.8 ¦g/l) of unsupplemented ewes was least in spring when pasture was actively growing and its selenium concentration was declining. Plasma and liver selenium concentrations were least at weaning, both in lambs from unsupplemented ewes (3 ¦g/l and 0.093 mg/kg DM respectively) and from supplemented ewes (7 ¦g/l and 0.120 mg/kg DM respectively). Selenium supplementation of ewes resulted in elevated selenium concentrations in the plasma of their lambs up to 8 weeks of age. Plasma concentrations declined thereafter and by weaning, at c. 18 weeks, there was little difference between plasma selenium concentrations of lambs from supplemented and unsupplemented ewes. Despite a low selenium status of unsupplemented weaners, supplementation did not improve growth rate during the summer and autumn, the period when problems of selenium inadequacy have been recorded previously.