Infertility in a bull with a nuclear sperm defect: A case report

A Simmental bull with a history of low fertility, both by natural service and artificial insemination, was presented for examination. Two previous semen evaluations had revealed no specific semen abnormalities that would support the breeding history. A comprehensive cytochemical analysis of the bull's ejaculate revealed a complex nuclear lesion affecting over 80% of sperm. This condition was expressed in abnormal shaping of the nuclei, with deficient distribution, condensation and stabilization of the nucleoplasm. These abnormalities were associated with various-sized intranuclear pouches or depressions. The acrosome was moderately involved and the tail was relatively free of abnormalities resulting in normal sperm motility.Two controlled breeding trials utilizing a total of 15 super-ovulated females were conducted to evaluate the bull's fertilization rate. Combined data demonstrated an 18% ($\text{23}\text{128}$) fertilization rate of recovered ova. At the same time, the fertilization rate of seven bulls classified as satisfactory potential breeders was 72% ($\text{353}\text{490}$).Data from two embryo transplant units regarding ova collected from eight donor females inseminated with semen from this bull revealed a fertilization rate of 41% ($\text{30}\text{73}$). Of the fertilized ova, 37% ($\text{11}\text{30}$) were degenerate and were not transferred. A pregnancy rate of 57% ($\text{11}\text{19}$) resulted from the transfer of 19 fertilized ova.A natural breeding pregnancy rate of 5% ($\text{2}\text{42}$) and artificial breeding pregnancy rate of 8% ($\text{15}\text{180}$) support the breeding trial results.