Genetic variation within and between European cattle breeds

Effective conservation strategies for livestock populations will require breeds to be characterized on the basis of their genetic attributes. Genetic markers can be used to survey breed relationships and within-breed population structure. They can also be used for the identification of breeds. In this study markers were used to investigate genetic relationships among thirty-seven European cattle breeds. Blood group (A,B,C,F,L,S,Z) and serum protein (transferrin and albumin) polymorphisms in 18,859 animals were analysed. French, Italian and Channel Island breeds were found to have generally higher heterozygosities and greater numbers of alleles than breeds from Britain and Northern Europe. Genetic distances among breeds were estimated, and two major breed groups were identified. French, Italian and Channel Island breeds clustered together in one group, while the second group consisted of breeds from Britain and Northern Europe. All breeds were significantly different from one another (p < 0.0001). In general, relationships among breeds reflected their geographical origin and common ancestry, rather than the agricultural use for which the breeds have been selected. Genetic differentiation among populations of Hereford cattle from different countries, and change in the genetic structure of the British Hereford population over time were investigated using blood typing data collected between 1966-1996. Genetic distances were estimated among Hereford populations from Britain, Ireland, Sweden, Canada and New Zealand, and six other beef breeds. The Hereford populations clustered together, and were significantly different from the other breeds. Irish, New Zealand and Swedish Herefords were significantly different from most other Hereford groups. Canadian Herefords were significantly different from groups with 100% British ancestry, but not from groups with hybrid (British and Canadian) ancestry or polled groups. However, there was no distinction between horned and polled groups from the same country. The proportion of Canadian genes in the hybrid population was estimated at 0.65 (± 0.21). Canadian Hereford groups were found to be least heterozygous of the Hereford groups. The replacement of the British Hereford population with Canadian animals may lead to a loss of genetic variation in the long-term. Genetic markers provide a potentially powerful way of identifying the breed of individual animals. Microsatellite markers were found to be more powerful than diallelic markers for distinguishing among breeds, approximately one microsatellite to six diallelic markers was required to achieve the same power of discrimination. The number of markers needed to achieve a given error rate could be reduced by selecting the most discriminatory individual markers. However, the exact number of markers required depends on the number and type of breeds to be identified. The development of new DNA technologies is making screening of large numbers of loci economically viable, which will enable genetic differences between breeds to be more precisely understood and their genetic histories to be more accurately defined.