Genetic gain & Inbreeding

Quantifying genetic load through joint modeling of inbreeding depression and inbreeding load for litter size in rabbits

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Abstract

Genetic load is the reduction in population fitness caused by deleterious alleles. It comprises a realized component, expressed through homozygosity as inbreeding depression (bF), and a masked component - the individual inbreeding load (IL) -representing recessive deleterious alleles hidden in heterozygotes and reflecting each ancestor's potential to cause inbreeding depression. This study aimed to jointly estimate inbreeding depression (bF) and individual inbreeding load (IL) for the number of kits born alive (NBA) in Pannon White rabbits, accounting for both maternal (bFdoe, ILdoe) and litter (bFlit, ILlit) inbreeding effects within a single model. A total of 33,521 kindling records from 7,594 does and a pedigree of 43,858 animals were analyzed. The mean NBA was 7.02 ± 3.43, and mean inbreeding coefficients were 0.05 ± 0.04 for does and 0.06 ± 0.05 for litters. A Bayesian linear mixed model was applied, in which inbreeding was decomposed into partial coefficients, and ILdoe and ILlit were estimated as independent random effects. The Gibbs sampler was run for 10,000,000 iterations with a burn-in of 4,000,000 and thinning every 10th sample. Convergence was confirmed by Geweke diagnostics, and posterior means with 95% highest posterior density (HPD) intervals were used to assess parameter uncertainty. Both inbreeding depression estimates were negative, with posterior means (HPD95%) of -2.99 [-5.48, -0.49] and -5.17 [-6.89, -3.48] kits per 100% inbreeding for does and litters, respectively. Additive genetic variance was σ²a = 0.56 [0.40, 0.73]. The variance of maternal IL (σ²idoe = 118.47 [6.83, 261.55]), exceeded that of litter IL (σ²ilit = 72.24 [2.22, 179.99]), suggesting greater heterogeneity among maternal components contributing to IL. This variance values refers to a hypothetical individual that is 100% inbred, a situation that is practically impossible. After reescaling to an individual with an inbreeding coefficient of 0.1, which is more representative of realistic scenarios, the corresponding variance values are 1.18 and 0.72, respectively. Herd-year-season variance was σ²h = 0.25 [0.19, 0.32], permanent environmental variance σ²p = 0.98 [0.82, 1.15], and residual variance σ²e = 9.80 [9.64, 9.97]. These results demonstrate that both maternal and litter inbreeding contribute significantly to inbreeding depression in reproductive performance. Joint modelling of maternal and litter IL provides a robust framework for quantifying inbreeding load and emphasizes the importance of accounting for both components to mitigate inbreeding depression while maintaining genetic progress.

Keywords: 2026

How to Cite:

Hervás-Rivero, C., Nguyen, A., Kövér, G., Bokor, Á., Nagy, I., Curik, I. & Varona, L., (2026) “Quantifying genetic load through joint modeling of inbreeding depression and inbreeding load for litter size in rabbits”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2271065. doi: https://doi.org/10.31274/wcgalp.23406

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