Effects of radioactive caesium on bull testes after the Fukushima nuclear plant accident

We aimed to investigate the effect of chronic radiation exposure associated with the Fukushima Daiichi Nuclear Plant accident on the testis from 2 bulls. Estimated dose of internal exposure in one bull was 0.7–1.2 mGy ((134)Cs) and 0.4–0.6 mGy ((137)Cs) and external exposure was 2.0 mGy ((134)Cs) and 0.8 mGy ((137)Cs) (196 days). Internal dose in the other was 3.2–6.1 mGy ((134)Cs) and 1.8–3.4 mGy ((137)Cs) and external dose was 1.3 mGy ((134)Cs) and 0.6 mGy ((137)Cs) (315 days). Sperm morphology and spermatogenesis were within normal ranges. (134, 137)Cs radioactivity was detected but Cs was not detectable in the testis by electron probe microanalysis. Thus, adverse radiation-induced effects were not observed in bull testes following chronic exposure to the above levels of radiation for up to 10 months. Since we could analyse a limited number of testes, further investigation on the effects of ionizing radiation on spermatogenesis should be extended to more animals.