An attempt was made to determine the concentration of unbound estriol (E3) in the blood of female mink in the periconceptional period in terms of the possible use of this hormone in the diagnosis of pregnancy. The studies involved 54 Black female mink. Blood was collected before mating, on 27 February (non-pregnant females), and after mating, on 5 April. The E3 serum concentrations before mating were statistically lower (P≤0.01) compared to those measured after mating. No significant differences in E3 concentration between females of different gestational status were found. Striking is the high number of females that had been marked as mated, yet never gave birth (approx. 31%). Free estriol serum concentrations over the first 10 days of putative gestation is not a good tool in mink pregnancy detection.

Key words: Estriol, Mink, Periconceptional period, Pregnancy