Context: It’s well-documented that most economic traits have a complex genetic structure
that is controlled by additive and non-additive gene actions. Hence, knowledge of the
underlying genetic architecture of such complex traits could aid in understanding how
these traits respond to the selection in breeding and mating programs. Computing and having estimates of the non-additive effect for economic traits in sheep using genome-wide
information can be important because; non-additive genes play an important role in the
prediction accuracy of genomic breeding values and the genetic response to the selection.
Aim: This study aimed to assess the impact of non-additive effects (dominance and epistasis) on the estimation of genetic parameters for body weight traits in sheep.
Methods: This study used phenotypic and genotypic belonging to 752 Scottish Blackface
lambs. Three live weight traits considered in this study were included in body weight at 16,
20, and 24 weeks). Three genetic models including additive (AM), additiveþ dominance
(ADM), and additive þ dominanceþ epistasis (ADEM), were used.
Key results: The narrow sense heritability for weight at 16 weeks of age (BW16) were 0.39,
0.35, and 0.23, for 20 weeks of age (BW20) were 0.55, 0.54, and 0.42, and finally for 24 weeks
of age (BW24) were 0.16, 0.12, and 0.02, using the AM, ADM, and ADEM models, respectively. The additive genetic model significantly outperformed the non-additive genetic model
(p < 0.01). The dominance variance of the BW16, BW20, and BW24 accounted for 38, 6, and
30% of the total phenotypic, respectively. Moreover, the epistatic variance accounted for 39,
0.39, and 47% of the total phenotypic variances of these traits, respectively. In addition, our
results indicated that the most important SNPs for live weight traits are on chromosomes 3
(three SNPS including s12606.1, OAR3_221188082.1, and OAR3_4106875.1), 8 (OAR8_
16468019.1, OAR8_18067475.1, and OAR8_18043643.1), and 19 (OAR19_18010247.1), according to the genome-wide association analysis using additive and non-additive genetic model.
Conclusions: The results emphasized that the non-additive genetic effects play an important role in controlling body weight variation at the age of 16–24 weeks in Scottish
Blackface lambs.
Implications: It is expected that using a high-density SNP panel and the joint modeling of
both additive and non-additive effects can lead to better estimation and prediction of genetic parameters.