209 Prevalence of subclinical selenium deficiency in Oregon grazing sheep using whole blood analysis

The objective of this study was to understand the status of microminerals in sheep across the state of Oregon and determine the association with management, including dietary supplementation, with major focus on Se, as Oregon is a region considered low in soil Se. Fifty-five sheep farms encompassing >70% of the counties in Oregon were enrolled in this study, and tentatively, 10% of the ewes in the flock were selected (but not fewer than 3 and not more than 10 ewes). To be enrolled, ewes must have been dry (non-lactating), fed a local forage diet for the last 3 consecutive months, be between the ages of 2 and yr old, have lambed at least once before, have a body condition score between 2 and 4 on a 5-point scale, and observably healthy. A questionnaire regarding rearing practices, mineral supplementation protocol, and observed health or production deficits was sent to the producers. Whole blood (3 mL) was collected in a royal blue trace mineral-free tube from each animal and digested in concentrated nitric acid and hydrogen peroxide, then diluted in distilled water, and analyzed via ICP-MS. Commercial standards were used to calibrate the ICP-MS for >14 microminerals and heavy metals including Se. Data were normalized using Indium as an internal standard before quantification using the standard curve. Available normal reference ranges for whole blood for all minerals were identified using published literature. For Se in whole blood, normal ranges were defined as 120 to 350 ng/mL. Intra and inter-flock variance was plotted, and the proportion of animals in each farm below or above the normal range was quantified. Interflock spread was between 8 and 519 ng/mL with a median of 211 ng/mL. Forty-seven percent of farms had at least one deficient animal. Results indicated that subclinical Se deficiency (< 120 ng/mL without reported production deficits) was prevalent in forage-fed dry ewes even when mineral supplements were offered ad-lib. Overall, these findings indicate a need to screen for Se deficiency to evaluate the efficacy of the mineral supplementation protocol.