The breed structure and genetic analysis of the pedigree cattle breeds in Australia

(i) The breed structure and genetic history of the pedigree Jersey breed in Australia are analysed by pedigree sampling methods. (ii) The breed structure may be divided into four levels, with imported animals at the top determining the genetic make-up of the breed. Animals imported since 1900 have made a genetic contribution to the breed in 1950 of 61.8 per cent. At least two substructures exist within the breed, based respectively on the major herds in Queensland and those in the rest of Australia. (iii) The genetic contribution to the breed of the most important of the herds is only 7.0 per cent. (iv) Determination of the percentage direct relationship of important animals in five sample years shows that no one animal has made a major contribution to the genotype of the breed. (v) The degree of inbreeding (base year 1900) is calculated. The total inbreeding in 1950 (4.19 per cent.) comprises 1.31 per cent. current inbreeding, 0.51 per cent. long-term inbreeding, and 2.37 per cent. strain inbreeding. The index of subdivision calculated from the non-current and long-term inbreeding is 5.65, indicating that the breed is subdivided into strains. (vi) The effective generation length for each of the pedigree breeds – Jersey, Australian Illawarra Shorthorn, Friesian, Ayrshire, and Guernsey – in Australia is 5 years. Most bulls are used when they are 1-3 years old, and are then lost to the pedigree industry. It is shown that the bull requirements of the above breeds could be met by the progeny of performance-recorded animals. Whether this would increase the rate of genetic improvement is discussed briefly. (vii) Genetic improvement in the Jersey breed could best be achieved by: ( a ) stopping further importation; ( b ) closing the breed in each environment and concentrating selection within these regions to develop strains adapted to each particular environment; ( c ) selecting on production records rather than using genetically unknown sires and dams, particularly in the major breeders' herds.