Heritability estimates and predictive ability for pig meat quality traits using identity-by-state and identity-by-descent relationships in an F2 population

Abstract

Genomic relationships can be computed with dense genome-wide genotypes through different methods, either based on identity-by-state (IBS) or identity-by-descent (IBD). The latter has been shown to increase the accuracy of both estimated relationships and predicted breeding values. However, it is not clear whether an IBD approach would achieve greater heritability ( $h^2$ ) and predictive ability ( ${\hat{r}}_{y,\hat{y}}$ ) than its IBS counterpart for data with low-depth pedigrees. Here, we compare both approaches in terms of the estimated of $h^2$ and ${\hat{r}}_{y,\hat{y}}$ , using data on meat quality and carcass traits recorded in experimental crossbred pigs, with a pedigree constrained to only three generations. Three animal models were fitted which differed on the relationship matrix: an IBS model ( $G_{\mathrm{IBS}}$ ), an IBD (defined within the known pedigree) model ( $G_{\mathrm{IBD}}$ ), and a pedigree model ( $A_{22}$ ). In 9 of 20 traits, the range of increase for the estimates of ${\sigma }_u^2$ and $h^2$ was 1.2-2.9 times greater with $G_{\mathrm{IBS}}$ and $G_{\mathrm{IBD}}$ models than with $A_{22}$ . Whereas for all traits, both parameters were similar between genomic models. The ${\hat{r}}_{y,\hat{y}}$ of the genomic models was higher compared to $A_{22}$ . A scarce increment in ${\hat{r}}_{y,\hat{y}}$ was found with $G_{\mathrm{IBS}}$ when compared to $G_{\mathrm{IBD}}$ , most likely due to the former recovering sizeable relationships among founder F₀ animals.

Keywords: cross-validation; genomic prediction; heritability; identity by descent; pigs; predictive ability.