Association between a polymorphism in the IGF2 gene and finishing weight in a commercial rabbit population.

Insulin-like growth factor 2 (IGF2) is a key regulator of skeletal myogenesis during developmental stages and is involved in many other growth related processes and several diseases. We re-sequenced the three coding exons of the rabbit IGF2 gene, including part of untranslated and intronic regions, for a total of 1037 bp in 8 rabbits of different breeds and lines and identified an indel of 1 bp in the intron after the first coding exon (EMBL accession numbers: HE608866 and HE608867; c.156+61delA). This indel has been genotyped by PCR-RFLP in 66 rabbits of different breeds to evaluate its allele frequency distribution in a population of 304 performance tested rabbits of a commercial line reared in the test station of Gruppo Martini (Italy) to evaluate association with finishing weight. Association analysis between the c.156+61delA indel and weight at 70 days of age was carried out using the procedure MIXED of SAS. The marker was associated with finishing weight (P<0.05). Least square means  standard errors of the three genotypes were: genotype A/A = 2644.7235.18 g (no. of animals = 101); A/del = 2681.9431.85 g (154); del/del = 2735.6539.60 (49); with estimated additive genetic effect (45.4718.13 g, P=0.013). The frequency of the favourable allele (del) in this commercial population was much higher (41.5%) compared to what we observed in all fancy breeds that are not selected for growth efficiency. However it was not fixed probably as a result of recurrent crossbreeding with several other blood lines or as a result of possible unfavourable effects of this allele on other production/fitness traits. This question should be answered before applying this IGF2 polymorphism in marker assisted selection to improve growth rate in meat rabbits.