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Inbreeding Trends and Application of Optimized Selection in the UK Holstein Population

Scottish Agricultural College, Edinburgh, EH9 3JG, Scotland, UK

Corresponding author: J. F. Kearney; e-mail: f.kearney{at}ed.sac.ac.uk.

Important increases in the rates of inbreeding have recently been observed in dairy cattle populations, and methods have been proposed to address these increases. The aims of this study were to estimate the current level and rates of inbreeding in the UK Holstein population and to investigate the potential of applying optimized selection to manage the rates of inbreeding. Inbreeding coefficients were calculated for the entire UK Holstein population using 1940 as the base year. Rates of inbreeding were obtained for 3 time periods by regressing mean inbreeding coefficients on the year of birth of the animals. The expected average pedigree index and expected inbreeding of offspring using optimized contributions for a given set of selection candidates was compared to the expected pedigree index and inbreeding of offspring for the same set of selection candidates using observed contributions. The rate of inbreeding in the UK Holstein population has increased substantially since 1990 when compared to previous time periods. This increase is most likely due to the large influence of a few related sires on the breed in the mid- to late 1980s. The introduction of the individual animal model in the early 1990s may also have contributed to increased inbreeding. Optimized selection appears to represent a promising selection tool, not only to manage rates of inbreeding, but also to increase genetic gain at the same rate of inbreeding.

Key Words: inbreeding • Holstein • optimized selection

Abbreviation key: £PLI = profitable life index, £PIN = production profit index, F = difference between offspring and parent average inbreeding coefficients, Top 2000 = parents of the top 2000 males born in 2002, Top 1000 = parents of the top 1000 males born in 2002.

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