An Analysis of the Age Patterns of Sires in the Hokkaido Dairy Population

Abstract

Pedigree information on the 819, 904 cows which were registered at Hokkaido Branch, the Holstein Association of Japan from Apr. 1st 1975 to Dec. 2nd 1983, was used to investigate the breeding patterns of dairy cows in Hokkaido. On the basis of the number of the registered cows born in Hokkaido, it was found the offspring of Hokkaido sires continue to decrease in number year by year, and that offspring of Canadian sires which produced the most female offspring from 1976 to 1980 tended to decrease in number after then. The production of offspring by American sires has continued to increase since 1978 and accounted for 55.6 per cent of the total cows born in 1983. Large variation was observed among sires and between home-bred and foreign-bred sires (American and Canadian sires) as to the number of female offspring which each sire produced in Hokkaido. Foreign-bred sires which were produced in the USA and Canada and introduced to Hokkaido, were extensively used for breeding for long period and produced many female offspring, whereas most Hokkaido sires left AI service at a younger age having produced a relatively small number of offspring. They tend to be in service at private farms other than the organized AI centers. The average generation interval from sires to female offspring were estimated to be 5.4, 8.0 and 8.2 years for Hokkaido, American and Canadian sires respectively.