In our previous report we speculated about the possibility that some species had high levels of spontaneous micronucleated erythrocytes (MNE) just in a juvenile stage, this is, that the MNE diminish as the reticuloendothelial system matures. Here we show this effect in species including rat, rabbit, pig, dog, cat, gray squirrel, lion, giraffe, white-tailed deer, opossum and even human. The number of spontaneous MNE that we found in 43 species is shown, and the proportions of polychromatic and normochromatic. This is our third report on spontaneous MNE in different species. We obtained 189 peripheral blood samples of mammals, birds and reptiles. From 12 species we obtained only one sample, and 16 were reported previously, but now the size of the sample has been increased. The species with the highest spontaneous MNE were the Vietnamese potbelly pig (with the highest MNE number), Bengal tiger, capuchin monkey, puma, ferret, owl, hedgehog, squirrel monkey, pig and white-tailed deer. These species could be used as monitors for genotoxic events.