Abstract :
Sheep grazed in Se-deficient areas without access to Se supplementsmay be Se deficient by
the end of the grazing season. One limitation to feeding mineral mixes and feeds containing
inorganic Se-supplements is the short duration of Se storage in the animal. Another is that
Se supplementation may be limited by country-specific regulations. However, the use of
feedstuffs naturally high in Se to deliver surpranutritional levels of Se is not regulated. The
purpose of this study was to evaluate Se status in sheep after short-term exposure to high-
Se-fertilized forage vs. a commonly used mineral supplement containing inorganic sodium
selenite. Selcote Ultra® was mixed with nitrogen fertilizer in the form of urea and applied to
pasture at a rate of 3.4 kg Selcote Ultra®/ha and 67.4 kg nitrogen/ha. Thirty ewes were randomly
divided into two groups.Onegroup of 15 ewes grazed Se-fertilized pasture for 40 days
and had no mineral supplementation. The other group of 15 ewes grazed a non-Se-fertilized
pasture and received a custom made mineral supplement containing 200 mg/kg sodium
selenite for 40 days. Subsequently the two groups of ewes were combined and grazed a
non-Se-fertilized pasture and had no mineral supplementation. Sheep were bled pre- and
post-treatment and then every 2–4 weeks thereafter for approximately 9 months to assess
whole-blood Se concentrations. Whole-blood Se concentrations were higher (P < 0.0001)
immediately post-treatment in sheep grazing Se-fertilized forage (573±20 ng/ml) compared
to sheep receiving mineral supplement containing Se (286±20 ng/ml), and were
still higher (P < 0.0001) at the end of 9 months (97±7 ng/ml vs. 61±7 ng/ml, respectively).
Whole-blood Se concentrationswere within the normal reference interval (150–500 ng/ml)
for a longer period of time in sheep grazing Se-fertilized forage (7 months) compared to
sheep receiving mineral supplement containing inorganic Se (4 months). No sheep showed
clinical signs of ill-effects from Se supplementation. In conclusion, short-term exposure of
sheep to Se-fertilized forage results in whole-blood Se concentrations sufficient to maintain
adequate concentrations throughout grazing periods when there is limited access to
Se supplements.
