Heterotic effects on litter traits in crossbreeding experiment involving Egyptian rabbit lines

A four-years crossbreeding experiment was performed involving two synthetic rabbit lines of APRI (A) and Moshtohor (M) where bucks of the APRI line were mated with does of the Moshtohor line to produce F₁ crossbred (½A½M), followed by inter-se mating to obtain F₂ crossbred (½A½M)². A total of 669 litters produced from 184 bucks and 394 does were used in analyzing litter size at birth (LSB) and weaning (LSW), litter weight at birth (LWB) and weaning (LWW) and pre-weaning mortality (PM). Heritability estimates for the targeted traits were low to moderate, ranging from 0.11 to 0.27. APRI line had the lowest range in predicted breeding values (PBVs) for all litter traits. The ranges in PBV for the four genetic groups were high and ranging from 0.59 to 1.0 kit for LSB, 2.4 to 3.0 kit for LSW, 26.5 to 33.9 g for LWB, 411.6 to 515.5 g for LWW and 20.9 to 24.8% for PM. The estimates of direct additive effects (G^I) and maternal effects (G^M) for litter traits were in favour of the Moshtohor line with percentages ranging from 1.2 to 16.3% for G^I and 1.4 to 20.5% for G^M. The estimates of direct heterosis (H^I) and maternal heterosis (H^M) were significantly positive for most litter traits with percentages ranging from 2.4 to 55.8% for H^I and 1.8 to 34.6% for H^M. In practice, it is recommended to use the APRI line as a sire group and Moshtohor line as a dam group in the crossbreeding program to synthesize new synthetic rabbit lines in Egypt.