Quantifying parent-of-origin variation in growth and reproductive traits of Kermani sheep

Records on growth and reproductive characteristics collected from 1993 to 2013 at the Breeding Station of Kermani sheep, south-east of Iran, were used for estimating genetic parameters related to parent-of-origin effects. The studied growth traits were birth weight (BWT), weaning weight (WWT), six-month weight (6MW), average daily gain from birth to weaning (ADG1), and average daily gain from weaning to six months of age (ADG2). The reproductive traits were litter size at birth per ewe lambing (LSB), litter size at weaning per ewe lambing (LSW), the sum of litter weight at birth per ewe lambing (LWB), and the sum of litter weight at weaning per ewe lambing (LWW). Models with and without imprinting (maternal and paternal) effects were compared by applying Akaike's information criterion (AIC). Maternal imprinting effects explained 14, 7, 24 and 5% of the phenotypic variances for BWT, WWT, 6MW and ADG1, respectively and their inclusion in the model decreased direct heritability estimates for BWT (from 0.07 to 0.05), WWT (from 0.29 to 0.23), 6MW (from 0.26 to 0.12) and ADG1 (from 0.20 to 0.17). Imprinting effects did not affect ADG2 and studied reproductive traits. The results indicated that a considerable proportion of the maternal imprinting effects overlap with direct additive genetic and maternal effects. Therefore, imprinting effects may be crucial for the genetic assessment of BWT, WWT, 6MW and ADG1 in Kermani sheep.