Effect of selenium applied to pasture on the selenium status of grazing sheep

Abstract

Blood selenium concentrations and liveweight gains were assessed for sheep grazing pastures treated with different selenium supplements over a 2-year period. Three 0.5 hectare irrigated blocks with pasture selenium concentrations of less than 0.04 μg/g DM were identified near Lincoln, Canterbury during 1997. Treatments applied in early November 1997 were: (1) 1 kg/ha of an experimental selenium product (SRSe5, containing 10g selenium); (2) 1 kg/ha of a commercially available slow release selenium product (positive control, containing 10g selenium) and (3) nil selenium treatment (negative control); all treatments used 60 kg urea/ha as the carrier. Treatments were stocked at 30 lambs/ha in November 1997. Liveweight gains and concentrations of blood selenium were monitored fortnightly for the first 4 months of the study and monthly thereafter. Following mating in April 1998, blood selenium concentrations and liveweight gains of spring born progeny were assessed. Ewes grazing the SRSe5 and positive control treatments had significantly greater concentrations of blood selenium than the negative control group and the concentrations for the SRSe5 group were significantly greater than from the positive control. Negative control ewes and their lambs were removed from the study at lambing due to low blood selenium concentrations and concerns regarding their health. Concentrations of blood selenium did not differ significantly between lambs of SRSe5 and positive control ewes born in the second year of the study. Lamb and ewe blood selenium concentrations were highly correlated. Liveweight gains did not differ significantly between SRSe5, positive control or negative control groups for ewes or lambs during either year of the study. This study demonstrated that the application of selenium to pastures is a highly effective longterm strategy by which concentrations of blood selenium may be elevated in sheep under New Zealand pastoral conditions. While liveweights did not differ significantly between treatments during either year of the study, the small numbers of animals used limited the power with which differences could be detected between treatments. Keywords: pasture, selenium, sheep, supplementation, topdressing