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Purging of inbreeding depression within the Irish Holstein-Friesian population

Sinéad Mc Parland12*, Francis Kearney3 and Donagh P Berry1

Author Affiliations

1 Teagasc, Moorepark Dairy Production Research Centre, Fermoy, Co. Cork, Ireland

2 Animal Genomics Laboratory, School of Agriculture, Food Science and Veterinary Medicine and Conway Institute of Biomolecular and Biomedical Research, College of Life Sciences, University College Dublin, Belfield, Dublin 4, Ireland

3 Irish Cattle Breeding Federation, Bandon, Co. Cork, Ireland

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Genetics Selection Evolution 2009, 41:16  doi:10.1186/1297-9686-41-16

Published: 21 January 2009

Abstract

The objective of this study was to investigate whether inbreeding depression in milk production or fertility performance has been partially purged due to selection within the Irish Holstein-Friesian population. Classical, ancestral (i.e., the inbreeding of an individual's ancestors according to two different formulae) and new inbreeding coefficients (i.e., part of the classical inbreeding coefficient that is not accounted for by ancestral inbreeding) were computed for all animals. The effect of each coefficient on 305-day milk, fat and protein yield as well as calving interval, age at first calving and survival to second lactation was investigated. Ancestral inbreeding accounting for all common ancestors in the pedigree had a positive effect on 305-day milk and protein yield, increasing yields by 4.85 kg and 0.12 kg, respectively. However, ancestral inbreeding accounting only for those common ancestors, which contribute to the classical inbreeding coefficient had a negative effect on all milk production traits decreasing 305-day milk, fat and protein yields by -8.85 kg, -0.53 kg and -0.33 kg, respectively. Classical, ancestral and new inbreeding generally had a detrimental effect on fertility and survival traits. From this study, it appears that Irish Holstein-Friesians have purged some of their genetic load for milk production through many years of selection based on production alone, while fertility, which has been less intensely selected for in the population demonstrates no evidence of purging.