Controlling Inbreeding by Constraining the Average Relationship Between Parents of Young Bulls Entering AI Progeny Test Programs

Abstract

In breeding is known to impair the health, fertility, and productivity of dairy cattle and other livestock species. Mating programs can address inbreeding concerns on the farm, at least in the short term, but long-term control of inbreeding in a dairy population requires consideration of relationships between young bulls entering AI progeny test programs. The present study discusses an application of optimal contribution methodology to selection of young AI bulls in the five major US dairy breeds. Elite cows and active AI sires from the Ayrshire, Brown Swiss, Guernsey, Holstein, and Jersey breeds were considered as potential bull parents. Genetic merit of selected sires and dams was maximized subject to various constraints on the mean additive genetic relationship within the selected group. Relationships between selected parents can be reduced substantially relative to current levels, but the corresponding reduction in genetic merit may be large. This loss in genetic merit occurs due to lower selection intensity, although it is mainly a reflection of a larger number of bull parents (with progeny more evenly distributed among these parents), rather than selection of genetically inferior "outcross" parents that wouldn't otherwise have been considered. Selected parents were generally older and slightly less inbred than those that would have been chosen had inbreeding been ignored. Although severe restrictions on relationships can be costly, in terms of lost genetic progress, it appears that moderate constraints can keep relationships at a manageable level without a significant loss in genetic merit. Cooperation between breed associations and several competing AI companies may be required to facilitate implementation of this methodology in dispersed populations, but if this can be accomplished, prospects for achieving a balance between inbreeding and selection seem positive.

Approaches to the management of inbreeding and relationship in the German Holstein dairy cattle population

“…The main relationship between selected bulls decreased from 0.393 to 0.308, but selection response was slightly lower (1.098 vs. 1.054). Weigel and Lin (2002) used the method of Meuwissen (1997) and constrained the level of inbreeding in the next generation and found that the optimal number of bull sires and bull dams decreased as the inbreeding constraint increased, particularly at low levels of inbreeding. Weigel and Lin (2000) compared the weighted mean lifetime net merit and the weighted mean adjusted lifetime net merit of the selected group.…”

“…Further on, Sonesson and Meuwissen (2000) developed an algorithm to combine OGC results with specific mating strategies. In dairy cattle, OGC was applied in the United Kingdom Holstein population (Kearney et al, 2004) and in different breeds in the United States (Weigel and Lin, 2002) for matings between bull sires and bull dams. They found increased genetic gain at the same rate of inbreeding compared to traditional selection schemes.…”

Management of genetic diversity in small farm animal populations

“…In research on non-endangered commercial cattle breeds (Ayrshire, Brown Swiss, Guernsey, Holstein and Jersey), Weigel and Lin (2002) address the use of restrictions on the increase of inbreeding in the selection of AI bulls. They find that the reduction in genetic gain is mainly due to the reduction in the selection intensity through the use of more parents, not because of the selection of genetically inferior animals.…”

Population structure of Brazilian Gyr dairy cattle

“…(Nomura et al, 2001;Weigel & Lin, 2002;Gutiérrez et al, 2003;Chikhi et al, 2004;Hagger, 2005). Unfavorable effects of inbreeding on milk yield and lactation length , and on weaning and yearling weights (Queiroz et al, 2000) were reported for Gyr cattle.…”