The experiment involved 30 clinically healthy female Beagle dogs aged approximately 70 days with estimated initial
body weight (BW) of 8 kg. The animals were randomly divided into two experimental groups (EI and EII) and a control group of 10 animals each. Group EI was intoxicated with 50 μg
zearalenone/kg BW per os for 42 days, group EII received 75 μg
zearalenone/kg BW per os for 42 days, and the control group was administered placebo per os for 42 days. The animals were weighed, and blood samples for analyses of the concentrations of
zearalenone, its metabolites,
progesterone and 17β-estradiol were collected seven times at seven-day intervals, one hour after
mycotoxin administration. Biotransformation of
zearalenone was observed in all groups throughout the experiment, and the highest percentage share of α-
zearalenol was reported in group EII on the last five sampling dates (0.637-0.788 ng/ml, i.e. percentage share of 57.96-73.64%). The above had a significant influence on the non-physiological concentrations of
progesterone and 17β-estradiol in both experimental (E) groups throughout the experiment. The lowest
progesterone levels (0.131 ng/ml) were observed in group EII during the last test, and high concentrations of 17β-estradiol were found in group EII on the last two sampling dates (17.434 and 21.581 ng/ml, respectively) in comparison with control. Inhibited proliferation, manifested by a slower rate of
body weight gain, was observed on the last but one day of
zearalenone administration in both experimental groups. Our results indicate that NOAEL doses have stimulating/adaptive effects, whereas doses above NOAEL values suggest that even very low
zearalenone doses can act as
endocrine disruptors with regard to
progesterone and 17β-estradiol.