Piglets’ birth weights are key to the survival and homogenous growth of litters and are, therefore, an important trait for an ethical, sustainable and cost-effective pork industry. This trait is influenced by parent-of–origin effects, such as maternal genetic effects and genomic imprinting. Maternal effects are already implemented into models used for genetic evaluations of birth weights in many different breeding programs. Moreover, previous studies have found significant imprinted loci associated with birth weights in pigs. However, none of these studies have accounted for maternal effects and genomic imprinting using only one model. Neglecting one epigenetic effect could result in an overestimation of this effect, where the effects are mistakenly confounded. Thus, the objective of this study was to estimate genomic imprinting effects and maternal effects in birth weights simultaneously. Birth weights of 42,367 Swiss Large White piglets with 49,734 individuals in the pedigree were collected between 2004 and 2022. Animal models including gametic effects as sire and as dam, as well as maternal genetic effects were implemented into Echidna MMS. A direct heritability of 0.13 and a maternal heritability of 0.03 was estimated. We found a negative genetic correlation between the gametic variance as sire and as dam of -0.61 and a small positive genetic correlation between gametic variance as dam and maternal genetic effects of 0.22. The share of the imprinting variance of the direct variance was 29.92%. Based on the assumption of previous studies that both effects exist in this polygenic trait, we separated genomic imprinting effects from maternal effects. This resulted in a shift in the values of the variance components. For the scenario when imprinting effects were not accounted for in the model, the maternal genetic variance was higher than the direct variance. When estimating a gametic variance as dam and as sire instead of one direct variance, the gametic variance as dam had the highest values, indicating that some amount of the variance accounted for genomic imprinting might be confounded in the maternal genetic effects if not accounted for in the statistical model. Here, we present preliminary evidence that genomic imprinting as well as maternal effects contribute to the birth weight in pigs. This is a first step towards better understanding epigenetic effects that influence birth weight expression for future selection decisions.
