Selenium supplementation: Confirmation of an effective 5-year delivery system for sheep

Abstract Selenium (Se) supplementation, in the form of a heavy density pellet (HDP), is a common management practice where livestock are grazing pastures low in this mineral. The aim of this study was to monitor changes in blood parameters resulting from Se supplementation to establish the effectiveness of the treatment. Two specific HDP products were tested in merino wethers grazing Se deficient pasture. Forty-five merino wethers were randomly assigned to one of three groups and treated as: (i) no supplement (control), (ii) dosed with 1 ‘Rumetrace™ Ezymin Sheep Selenium Pill’ (HDP-R) and 1 steel grinder, or (iii) dosed with 1 ‘Permatrace ® 3 Year Selenium Pellet For Sheep’ (HDP-P) and 1 steel grinder. All sheep were grazed as one flock on Se deficient pasture for the first 18 months, and then on pasture considered to be marginal in Se for another 42 months. Selenium concentration and glutathione peroxidase (GSHPx) activity in blood were measured as indicators of the response to supplementation. Blood was analysed at the start of the study and at 6 monthly intervals for a total of 5 years. At the commencement of the study, whole blood Se and GSHPx activity levels were consistent with Se deficiency. The control animals remained in that state for the duration of the study. Sheep treated with HDP-P expressed an initial surge in blood Se and GSHPx values, which after 36 months declined to levels comparable with the control group. In contrast, sheep treated with the HDP-R exhibited a more consistent elevation in the blood parameters which persisted for the length of the trial. This study shows that the HDP technology can be formulated and manufactured to last for at least 5 years.