POPULATION-STRUCTURE OF THE JAPANESE BROWN BREED

The population structure of the Japanese Brown in Kumamoto Prefecture was investigated with pedigree analysis. Two hundred heifers were rand omly sampled, in 1960, 1970, 1980, and 1990. Population genetic parame ters, i.e. F-statistics, index of subdivision, generation interval, ef fective population size, and effective number of sires, were estimated . The effective number of sires decreased, most dramatically, from 197 0 to 1980. The average inbreeding coefficient (F-IT) increased, from 0 .64% in 1960 to 5.43% in 1990. F-ST increased in parallel with F-IT, w hile F-IS remained low. From 1960 to 1980, the index of diversity show ed a decreasing trend, but this improved a little, with the index at 1 .1 in 1990. The generation interval tended to be longer year by year, and was 5.52 during 1980-90. On the other hand, N-c decreased, from 72 4.6 before 1960 to 40.1 at the present The population structure of the Japanese Brown is not problematical at present, when considering F-IT , but the irreversible inbreeding coefficient (F-ST) increases constan tly.