Migration of pedigree Jersey cattle in Australia

Abstract

Australia has been divided into 13 climatic regions. One hundred heifers and 50 bulls were taken at random for each region, their two-generation pedigrees traced, and the origin of each ancestor noted. Immigration is higher for the male sample than for the female. The genetic replacements (percentage of genes brought into the region during one generation) are 34.7 and 24.1 per cent. respectively. The replacement indices (percentage of each type of ancestor bred in a different region) are 53.3 and 38.1 for sires of the male and female samples respectively and 16.0 and 10.1 for dams, which indicates that migration is higher for sires than for dams. Regions 3 (semi-coastal Queensland), 7 (central coast, New South Wales), and 10 (Gippsland, Victoria) are the main breeding regions. Regions 11 (southwestern Victoria and South Australia), 12 (Tasmania), and 13 (Western Australia) have low immigration rates and are consequently semi-isolated from the rest of the breed. Within these semi-isolated regions, however, movement is highest. Further, although there is considerable migration between the four regions of Queensland (regions 1-4), the Queensland group is semi-isolated from the rest of the breed. Between region migration is mainly between adjacent regions, with some migration into all regions from the main breeding regions. All regions export and import bulls except region 12 (Tasmania,) and region 13 (Western Australia). The number of Breeders' Herds (herds supplying sires to other pedigree herds) is mainly a function of the number of herds within a region. The migration rate in the Australian Jersey appears to be considerably less than in Friesians, Shorthorns, or Ayrshires in the United Kingdom. Since most migration is between adjacent regions, this low rate of migration and geographic isolation together favour the development of semi-isolated and therefore possibly locally adapted strains. It is suggested that this pattern should he maintained until the importance of genotype-environment interactions is determined.