Estimation of the variance due to parent-of-origin effects for productive and reproductive traits in Lori-Bakhtiari sheep

Parent-of-origin effects are often excluded from models used for estimating of additive and non-additive genetic variances. Omission of parentally-linked genetic factors, such as imprinting, from statistical models has potential to induce profound bias during the estimation. In this study, parent of origin variance for productive and reproductive traits in Lori-Bakhtiari sheep was estimated using a gametic relationship matrix approach. The data set were obtained from a total of 7568 animals, collected from 1994 to 2012 from the Lori-Bakhtiari research flock at Shooli station in Shahrekord, Iran. Growth traits were included birth weight (BWT), weaning weight (WWT), 6-month weight (WT6), 9-month weight (WT9), yearling weight (WT12), average daily gain from birth to weaning (ADGa), and from weaning to 6-month (ADGb). In addition, litter size at birth (LSB), litter size at weaning (LSW), litter mean weight per lamb born (LMWLB), and litter mean weight per lamb weaned (LMWLW) were analyzed as basic reproductive traits, and total litter weight at birth per ewe lambing (TLWB) and total litter weight at weaning per ewe lambing (TLWW) as composite reproductive traits. Models including or excluding maternal and paternal imprinting effects were compared using the ayesian information criterion (BIC). For all growth traits, except WT6 and WT12, adding maternal imprinting effects into the models decreased BIC, with estimates ranging from 10.5% (WWT) to 23.3% (BWT) of the total phenotypic variance. Paternal imprinting effects, in the other hand, was estimated as 6.9% of the total phenotypic variance for ADGb. For reproductive traits, maternal imprinting effects explained up to 6% of total phenotypic variance for TLWW. Adding paternal or maternal imprinting to the models decreased the direct additive genetic, maternal additive genetic and maternal permanent environmental variance for the growth traits.