CROSSBREEDING EFFECTS AND POLYMORPHIC ASSOCIATIONS OF GENOTYPES OF GH GENE WITH GROWTH TRAITS IN RABBITS

A simple crossbreeding experiment between two new synthetic rabbit lines (APRI and Moshtohor) was conducted to estimate the crossbreeding effects (direct additive, maternal additive and heterosis) on post-weaning body weights (BW) at 4, 6, 8, 10 and 12 weeks of age and daily weight gains (DG) during the intervals from 4 to 6, 6 to 8, 8 to 10 and 10 to 12 weeks, and to detect the polymorphic associations of the genotypes of GH gene with post-weaning body weight and daily gain traits. Four genetic groups of APRI (A-line), Moshtohor (M-line) and their simple F1 cross (½A½M) in addition to V-line rabbits (as a reference population) were used in this study.PCR-RFLP technique was applied using BstUI restriction enzyme SNP for genotyping the growth hormone gene (GH) (TT, TC and CC) genotypes. Heritabilities estimated by VCE program for body weights and daily weight gains were mostly low or moderate and ranging from 0.05 to 0.18. The percentages of direct additive effects on body weights were significantly (P<0.01) in favour of Moshtohor line by 2.7, 4.3, 1.4, 2.6 and 2.9 % at 4, 6, 8, 10 and 12 weeks and by 8.7, 15.9 and 18.6 % in daily weight gains at DG4-6, DG6-8 and DG8-10, respectively. The percentages of maternal effects on body weights at 4, 6, 8, 10 and 12 weeks were also significantly in favour of Moshtohor line by 2.8, 5.4, 3.5, 3.5 and 3.1%, respectively and ranged from 1.8 to 15% for daily weight gains in weight. The percentages of direct heterosis were significantly positive by 3.1, 8.1, 8.2, 5.2 and 3.8 % for body weights at 4, 6, 8, 10 and 12 weeks and by 13.0, 7.8 and 9.6% for daily weight gains at DG6-8, DG8-10 and DG10-12, respectively. The associations of the genotypes of GH gene were polymorphic and had significant effects on most growth traits (P<0.05). There were significant differences (P<0.05) between the generalized least square means of the different genotypes (TT, CC and TC) of GH gene for body weights at 4, 6, 8, 10 and 12 weeks of age in V-line, M-line, A-line and ½A½M cross rabbits. The TC genotype was positively associated with an increase in body weights of V-line, M-line and A-line rabbits, while the TT genotype indicated an increase in body weights of ½A½M rabbits. The significant associations between GH gene and growth traits confirmed that this gene could be a candidate gene and may be used in Marker-assisted selection (MAS) to improve growth performance in rabbits.Conclusively, GH gene could be used as a candidate gene in genetic improvement programs to improve growth performance in rabbits.