Genetic diversity of a closed population of Japanese Black cattle in Hyogo prefecture

摘要

The Japanese Black in Hyogo prefecture has been almost closed population. In this paper, genetic diversity of the population was estimated. The materials used were 68,781 animals born in 1955 to 1998 and their pedigree records traced back to the population in 1937 or before. To assess the diversity, three types of parameters were estimated. Founder genome equivalents (N_(ge)) is the most comprehensive parameter, in which all the causes of the reduction of diversity are accounted for. Effective number of founders (N_(ef)) explains the cause of reduced diversity due to unequal contributions of founders. Effective number of non-founders (N_(enf)) accounts for the diversity reduced by genetic drift accumulated over non-founders generations. Index of genetic diversity (GD) was estimated by GD=1 - 1/(2N_(ge)). N_(ge) decreased gradually from 26.9 in 1955 and reached 2.2 in 1998. Before 1970, N_(enf) showed larger values than N_(ef), but the order was reversed in the later years. N_(enf) in the recent years was close to N_(ge). The index GD showed a sharp decline after 1980 and reached 0.78 in 1998. The major cause of the reduced genetic diversity was considered to be the bottleneck effect due to the concentrated use of breeding animals originated froma few founders.