Because of its morphological characteristics the defect was named the multinuclear–multiflagellar sperm defect.
All spermatozoa in the ejaculate were abnormal. Many of the spermatozoa had multiple nuclei and multiple sperm tails.
All spermatozoa lacked an acrosome, and only seldom did spermatozoa have a mitochondrial helix in the midpiece area.
Meiosis and spermiogenesis were severely affected in this otherwise phenotypically normal bull.
The sperm defects resembled the phenotype of a targeted gene knockout Hrb/ (HIV-1 Rev-binding/interacting protein) mutant mouse strain, which is expressed as sterility in males, while females remain fertile.
Since the father of this bull has been extensively used in at least three countries the defective gene has possibly become widespread in the red and white breeds (Ayrshire, Swedish Red and White, Norwegian Red) in the Nordic countries. However, it is not proved that the father of this bull is a carrier of this defect.
Source: C Kopp, A Sukura, E Tuunainen, I Gustavsson, M Parvinen, M Andersson (2007): Multinuclear-Multiflagellar Sperm Defect in a Bull - a New Sterilizing Sperm Defect. In:
Reproduction in Domestic Animals 42 (2), 208–213.
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