The ingestion of the secondary metabolites of plants can result in a multitude of physiological consequences in mammalian herbivores.However,only a few studies have been reported the influence of dietary tannins on small mammalian herbivore reproduction.We investigated the influence of quebracho tannin on root vole reproduction by incorporating quebracho tannin into the voles diets.We examined the effects of two concentrations (3%and 6%) of quebracho tannin provided in diets for 30 days on several reproductive characteristics of male and female voles.We determined serum testosterone level,sperm count,uterine and ovarian indices,number of ovarian follicles in two categories (small follicles,250-350 μm; large follicles,350-550 μm) ,litter size,body masses of the dams,and the mass of the young before weaning.We found that the ingestion of quebracho tannin by the male root vole significantly decreased serum testosterone level,but otherwise had no significant effect on the testicular and epididymal indices and sperm number.In females,quebracho tannin ingestion significantly decreased all the surveyed reproductive features,except the number of large follicles.This difference between the two sexes of root voles is considered to be attributable to the asymmetry of investment in gamete production between the sexes.