The aim of this work was the estimation of BLAD and CVM prevalence in Holstein heifers and bulls that produced the semen introduced to Morocco. The study was carried out on 1874 heifers imported from France, Germany and Netherlands between 2005 and 2006 and 221 bulls that produced the semen imported from Canada, USA and France between 1999 and 2007 . Based on the genotypes of sires and maternal grandsires mentioned on heifers' pedigrees, 2.1% and 17.5% of heifers introduced to Morocco were

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... tial BLAD and CVM carriers, respectively. No bull that produced the semen was BLAD-carrier, whereas 0.5% bulls were CVM carriers. The frequency of at risk matings, i.e. those between potential carrier heifers and known carrier bulls, was 0 for BLAD and 0.7% for CVM. The frequency of mating between non-carrier heifers and confirmed carrier bulls was 0.2% and 16.8% for BLAD and CVM, respectively. The BLAD and CVM allele frequencies in heifers varied from 0.01 to 0.12 and from 0.03 to 0.14, respectively. It was concluded that a surveillance programme should be implemented in Morocco in order to avoid the introduction and the dissemination of farm animal hereditary defects.