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This Article Full Text (PDF) All Versions of this Article: jas.2008-0897v1 87/1/72    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Casellas, J. Articles by Varona, L. Search for Related Content PubMed PubMed Citation Articles by Casellas, J. Articles by Varona, L.

Analysis of founder-specific inbreeding depression on birth weight in Ripollesa lambs

J. Casellas^*, J. Piedrafita, G. Caja and L. Varona^*,

^* Genètica i Millora Animal, IRTA-Lleida, 25198 Lleida, Spain , Grup de Recerca en Remugants, Departament de Ciència Animal i dels Aliments, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain Departamento de Anatomía, Embriología y Genética Animal, Universidad de Zaragoza, 50013 Zaragoza, Spain

joaquim.casellas{at}irta.es

Abstract

Although inbreeding (F) is a topic of major concern in animal breeding, estimates of inbreeding depression are usually obtained by modeling the overall F coefficient of each individual, without considering that the recessive (deleterious) genetic load of a given population may be unevenly distributed amongst the founder genomes. The founder-specific partial F coefficient is calculated as the identity-by-descent probability at any given autosomal locus related to a particular founder and allows a more detailed analysis of inbreeding depression on productive traits. Within this context, birth BW data from 2,459 Ripollesa lambs were analyzed under a hierarchical animal model without F-related covariates (Model 0), with inbreeding depression modeled by the overall F coefficient (Model F1), or by the partial F coefficient of 9 founders that made a relevant contribution to the population inbreeding (Model F2). A straightforward empirical Bayes factor (BF) was developed for testing statistical relevance of each F-related covariate, in which greater-than-1 values favored the model including the covariate. The deviance information criterion (DIC) clearly supported Model F1 (5,767.8) rather than Model 0 (5,771.2), suggesting that inbreeding depression had a relevant influence on birth BW data. The linear effect of inbreeding depression was statistically relevant in Model F1 (BF = 2.52 x 10³⁵), with lamb birth BW declining by -13.6 g with each 1% F increase. The quadratic effect of inbreeding depression was almost null in Model F1 (BF = 0.02), as suggested by the reduction in DIC (5,766.9) when this effect was removed from Model F1. On the other hand, Model F2 provided a similar DIC (5,767.9) value, with this parameter falling to 5,764.7 when non-relevant founder-specific inbreeding depression effects were removed. Substantial heterogeneity in founder-specific inbreeding depression was reported by Model F2, where estimates for 4 of the 9 founders did not differ from zero (BF between 0.05 and 0.42), whereas 5 founders originated moderate (-8.2 g for each 1% F increase; BF = 1.42) to high inbreeding depression (-96.2 g for each 1% F increase; BF = 8.80 x 10¹⁹). The substantial variability between founder estimates suggested that inbreeding depression effects may mainly be due to a few alleles with major deleterious effects. These results contribute valuable information that should help to achieve more accurate management of inbreeding in the Ripollesa breed.

Key Words: empirical Bayes factor • birth weight • founder • inbreeding depression • Ripollesa sheep