Abstract: The aim of the present study was to detect the proportion of Holstein bull carrying two recessive genetic defects including citrullinemia(CN) and deficiency of uridine monophosphate synthase(DYMPS) and carry out the pedigreed analysis, a more easier diagnostic method was developed as well. The genetic defects of CN and DYMPS was detected by PCRRFLP in 591 Holstein bulls, and the ASPCR technology was constructed for detecting the CN recessive deleterious gene. 2 CN carrier bulls and 1 DUMPS carrier bull were found, and the proportion of carrier bulls was 0.34% and 0.17%, respectively. Through pedigree analysis, the two CN carrier bulls were the descendants of Linmack Kriss King, and the DUMPS carrier bull was Skokie sensation Ned’s offsprings. The results indicate that it is necessary to establish early monitor system on genetic defects in all Holstein young, proven bulls and suspect cows, and put such information in their pedigree records. Through young bull preselection and selection and assortative mating system, carrier bulls could be avoided to enter into the national genetic improvement program, frequencies of the undesired recessive alleles could be greatly decreased as well.

Key words: Chinese Holstein, CN, DUMPS, genetic defect