The corkscrew sperm defect in Danish bulls--a possible indicator of nuclear fallout?

The characteristic corkscrew defect in the middle piece of the bull sperm was observed by the author in two infertile bulls in 1958 and described the following year. Since then the spermiograms of all Danish A.I. bulls (about 1200) have been examined yearly, and a total of 60 cases showing more than 2% corkscrew sperms in their semen have been recorded. The sperm defect was found mostly in older bulls and was often accompanied by testis degeneration. The Red Danish breed seems to be highly predisposed. The cause of the defect and the testis degeneration is obsecure. However, by comparing the curves for nuclear fallout during the observation period and the number of cases observed, there seems to be some correlation. It is striking that the maximum of ten new cases of the corkscrew defect was found in the peak year for nuclear testing in the atmosphere (1962), when a total of at least 133 tests were performed, thus polluting grassland all over the world. Since 1963, when a partial test ban treaty came into force, most nuclear testing has been done underground. From that time the number of yearly cases of the corkscrew defect in the Danish bull population has decreased and the defect is now practically non-existent. Attempts to produce the condition experimentally by feeding young bulls with the fission product Iodine131 have so far been negative.