Inbreeding, migration, and structure of the pedigree Large White pig population in Australia

Inbreeding, migration and structure of the pedigree Large White pig population in Australia were investigated by pedigree sampling methods. Inbreeding since 1905 of pigs registered in 1960 was 7.5 per cent. This comprised 1.0 per cent current and 6.5 per cent long term inbreeding. Strain development was indicated by an index of subdivision of 6.88. The most important ancestors, the sow 'Rossmoyne Duchess 31st' and the boar 'Lea Avon Jerry' had direct relationships to the 1960 population of 12 per cent and 8 per cent respectively. Migration of breeding stock within Australia was restricted. Breeders sought further afield for boars than for sows. Queensland and Victoria were favoured sources of breeding stock. Through four generations of ancestors, eight major herds contributed 83.07 per cent of the genes for the 1960 registrations, the most important herd contributing 14.54 per cent. The structure of the breed was represented by four strata of a hierarchy. Herds in all strata were widely distributed and obtained most of their sires from herds in the top stratum. The identities and relative positions of herds in the top stratum are indicated. There was a frequent exchange of stock between herds in the same locality. Most herds fluctuated in importance and were short lived, 61 per cent operating for fewer than five years. The need for the use of scientific breeding techniques is stressed, particularly for breeders with herds in the top stratum since they determine genetic progress in the breed.