Cytogenetic survey of Holstein bulls at a commercial artificial insemination company to determine prevalence of bulls with centric fusion and chimeric anomalies

Objective-To determine prevalence of Holstein bulls with chromosomal anomal ies, particularly the 1/21 centric fusion (CF), at a commercial artificial insemination (Al) company in the United States. Design-Cross-sectional cytogenetic prevalence study. Animals-All 606 Holstein bulls at a commercial Al company were cytogenetica lly screened to detect CF, chimerism, and other chromosomal abnormalities. Procedure-Lymphocytes from heparinized blood samples were cultured by stand ard cytogenetic techniques, and chromosome spreads were prepared for micros copic 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 identif ied as chimeras (ie, contained lymphocytes with male [XY] and female [XX] c hromosomes). One bull was sire or maternal grandsire to 85 of the bulls tes ted, 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 previ ous indications that CF is extremely rare in Holstein bloodlines available commercially via Al in the United Stales. However, chimeric bulls are more common, and they reportedly have decreased reproductive performance. Theref ore, identification of chimeric sires in the Al facility reported here and the possibility of de novo onset of CF at any time indicates that early cyt ogenetic screening should be encouraged for prospective bulls intended for use in Al programs.