Animals—All 606 Holstein bulls at a commercial AI
company were cytogenetically screened to detect CF,
chimerism, and other chromosomal abnormalities.
Procedure—Lymphocytes from heparinized blood
samples were cultured by standard cytogenetic techniques,
and chromosome spreads were prepared for
microscopic examination. Chromosomal abnormalities
were detected by examining 10 chromosome
spreads per bull. Pedigree analysis was performed.
Results—None of the bulls had any type of CF.
However, 6 bulls were identified as chimeras (ie, contained
lymphocytes with male [XY] and female [XX]
chromosomes). One bull was sire or maternal grandsire
to 85 of the bulls tested, and 739 of 1,212 (61%)
sire and maternal-grandsire possibilities were
accounted for by just 18 bulls.
Conclusions and Clinical Relevance—Analysis of
these results supports previous indications that CF is
extremely rare in Holstein bloodlines available commercially
via AI in the United States. However,
chimeric bulls are more common, and they reportedly
have decreased reproductive performance.
Therefore, identification of chimeric sires in the AI
facility reported here and the possibility of de novo
onset of CF at any time indicates that early cytogenetic
screening should be encouraged for prospective
bulls intended for use in AI programs. ( J Am Vet Med