[Selenium content in the blood cattle from Venezuela. I. Central and Portugueste zones].

Whole blood concentrations of selenium were determined in 776 dairy cows and calves from 28 farms located in three States (Aragua, Carabobo and Guárico) of the central zone of Venezuela and in Portuguesa State. Selenium levels largely varied according to both the geographic distribution and animals breed. Cattle from Guárico State showed the lowest average concentration (0.