Heritability of Productive, Reproductive and Carcass Traits in Pure-Bred and Cross-Bred Pigs: A Systematic Review and Meta-Analysis.

Heritability (h2) is a key parameter in animal breeding, but its magnitude and consistency across pure-bred (PB) and cross-bred (CB) pig populations remain poorly understood. This study aimed to compare heritability estimates between PB and CB populations for economically relevant traits through a systematic review and meta-analysis. A total of 28 studies (75 independent h2 estimates) were identified through searches in PubMed, Mendeley, Springer, ScienceDirect and Google Scholar (2000-2024). Multilevel random-effects models with logit transformation were applied. Traits were grouped into reproductive, growth, conformation and carcass categories. Reproductive traits showed low heritability (e.g., litter size: 0.06 in PB and 0.20 in CB; number born alive [NBA]: 0.07 in CB), whereas growth and carcass traits exhibited moderate values (e.g., average daily gain: 0.21 in PB and 0.31 in CB; intramuscular fat: 0.31 in PB and 0.29 in CB; pH: 0.23-0.26). Meta-regression did not detect a significant effect of population type (β = 0.124, p = 0.630), whereas studies accounting for non-additive genetic effects showed significantly different heritability estimates (QM = 4.35, p = 0.037), and high heterogeneity was observed across traits (I2 > 90%). These results indicate that cross-breeding does not systematically increase additive heritability. Instead, differences depend on trait type, likely reflecting differences in genetic architecture and the relative contribution of additive and non-additive genetic effects. Overall, these findings highlight the importance of population-specific genetic evaluations and context-dependent breeding strategies in pig production, supporting the complementary interpretation of heritability and pure-bred-cross-bred genetic correlation (rPC) within Combined Cross-bred and Pure-bred Selection (CCPS) programmes.