Mapping and association of GAD2 and GIP gene variants with feed intake and carcass traits in beef cattle (short communication)

Glutamate decarboxylase 2 (GAD2) is a major autoantigen in insulin-dependent diabetes, while glucose-dependent insulinotropic polypeptide (GIP) is a gastrointestinal hormone. Both genes are involved in insulin secretion and play a role in the regulation of feed intake and metabolic rate in animals. In the present study, we assigned the bovine GAD2 and GIP by RH mapping to BTA 13 and BTA 19, respectively. We discovered SNPs from these genes by a PCR-sequencing approach. We identified one SNP (T/C transition) from the 14^th intron of the bovine GAD2 gene and another SNP (A/C transversion) from the 4^th intron of the bovine GIP gene. Genotyping over 300 animals from five different beef populations revealed that the average allelic frequency for the GAD2 allele A was 0.48 and allele B 0.52, while for the GIP allele A 0.80 and allele B 0.20, respectively. There were significant associations observed between the GAD2 and GIP gene variants and Average Daily Feed Intake (ADFI) (p<0.05) in beef cattle. In addition, the GAD2 SNP was also associated with Meat Percent (MP) (p<0.05), whereas the GIP SNP was also significantly associated with Backfat Thickness (BF) (p<0.05) and Ratio of Feed-to-Meat (RFM) (p<0.05). There were no significant effects found for other traits. Although both SNPs could be used as candidate markers for MAS to improve feed intake and carcass traits, further investigations in large populations and in other breeds are recommended in order to understand the effect of the GAD2 and GIP polymorphisms on these quantitative traits in beef cattle.