Abstract :
The ratio between selenium (Se) concentrations in pairs of plasma and whole blood of sheep
after commencement of Se supplementation was calculated from data obtained from 10
independent investigations. The diets in the studies consisted of a variety of ingredients,
from the individual feeding of feedlot diets to grazing trials on Se-deficient pastures. Means
from 51 treatments, derived from 179 collections at various stages after commencement
of Se supplementation, were used to calculate the ratios. In one study it was found that
plasma Se concentration reached steady-state within 4 days of commencement, while Se
in whole blood reached steady-state only at the collection 60 days after supplementation
commenced. Using the 179 pairs, the ratio of whole blood and plasma stabilized at about 50
days after commencement when inorganic Se was supplemented, and at about 60–70 days
when the Se was in the organic form. The ratios stabilized when they were between 2:1 and
3:1, and remained practically constant from 50 days post onset of supplementation, when
plasma Se constituted 0.445 of whole blood Se concentration for the inorganic Se source
and 0.410 when the Se source was organic. It was concluded that after commencement of
Se intake, plasma Se concentration remains relatively constant from within 4 days of onset,
while whole blood Se concentration apparently reaches steady-state only after approximately
50 days. Before 50 days, whole blood Se seems not to be reliable to predict the Se
status of an animal. In a situation where Se intake is stable and Se requirements do not
fluctuate, a bloodplasma ratio of between 2:1 and 3:1 would be a guideline to indicate that
whole blood Se and plasma Se concentrations could both be used to assess the Se status of
sheep.
