Robertsonian Translocation and Its Effect on Fertility in Japanese Black Cattle
To confirm the distribution of chromosome abnormalities and their effects on fertility, a cytogenetic survey was carried out in five different herds of Japanese Black Cattle. The chromosome abnormality most frequently observed was the 7/21 Robertsonian translocation. This translocation was observed in a local herd at a fairly high frequency of 10.9% due to continuous use of the carrier bulls in artificial insemination. Analyses of breeding data failed to detect any significant difference in fertility between the normal animals and those with the 7/21 translocation. Semen characteristics of the carrier culls with the 7/21 translocation appeared normal. However, meiotic studies on the heterozygous bulls revealed the formation of aneuploid secondary spermatocytes from adjacent segregation. Trisomic embryos were detected in the cytogenetic study of embryos sired by the heterozygous bulls with the 7/21 translocation. The 7/21 translocation in the heterozygous state seemed to be associated with a slight reduction in fertility. Also, the 1/29 Robertsonian translocation, which has been reported in many breeds throughout the world, was widely distributed in Japanese Black Cattle.