Inbreeding trends and pedigree analysis of Irish dairy and beef cattle populations

¹ Teagasc, Moorepark Dairy Production Research Centre, Fermoy, Co. Cork, Ireland; School of Agriculture, Food Science & Veterinary Medicine UCD, Belfield, Dublin 4, Ireland
² Irish Cattle Breeding Federation, Bandon, Co. Cork, Ireland
³ School of Agriculture, Food Science & Veterinary Medicine UCD, Belfield, Dublin 4, Ireland
⁴ Teagasc, Moorepark Dairy Production Research Centre, Fermoy, Co. Cork, Ireland

^* To whom correspondence should be addressed. E-mail: sinead.mcparland{at}teagasc.ie.

	Abstract

The objective of this study was to determine inbreeding levels and analyze the pedigree of Irish purebred populations of Charolais, Limousin, Hereford, Angus, and Simmental beef cattle, as well as the Holstein-Friesian dairy breed. Pedigree analyses included quantifying the depth of known pedigree, average generation intervals, effective population size, the effective number of founders, ancestors, and founder genomes, as well as identifying the most influential animals within the current population of each breed. The annual rate of increase in inbreeding over the past decade was 0.13% (P < 0.001) in the Hereford, 0.06% (P < 0.001) in the Simmental, and 0.10% (P < 0.001) in the Holstein-Friesian breeds. Inbreeding in the other breeds remained relatively constant over the past decade. Herefords had the highest mean inbreeding in 2004 at 2.19%, whereas Charolais had the lowest at 0.54%. Over half of each purebred population in 2004 was inbred to some degree; the population with the highest proportion of animals inbred was the Hereford breed (85%). All six breeds displayed a generation interval of approximately 6 yr in recent years. The three most influential animals contributed between 11% (Limousin) and 24% (Hereford) of the genes in the purebred females born in 2004. Effective population size was estimated for the Hereford, Simmental, and Holstein-Friesian only, as 64, 127, and 75, respectively. The effective number of founders varied from 55 (Simmental) to 357 (Charolais), whereas the effective number of ancestors varied from 35 (Simmental and Hereford) to 82 (Limousin). Thus, despite the majority of animals being inbred, the inbreeding level across breeds is low, although rising at a slow rate in the Hereford, Simmental, and Holstein-Friesian.

Key Words: beef cattle, dairy cattle, inbreeding, pedigree analysis

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