Polymorphisms in the Growth Hormone Gene and Their Association with Pre-pullet Body Weight in Kuttanad Ducks of Kerala, India

Background: Kuttanad ducks are dual purpose native ducks found in Kerala state of India. Identification of single nucleotide variations in candidate genes like growth hormone gene and exploring their association with body weight at grower and pre-pullet stages is essential for the marker assisted selection of breeder ducks for genetic improvement. Methods: Genomic DNA was extracted from blood samples collected from 101 Kuttanad ducks. PCR-amplification of two duck growth hormone gene (dGH) loci viz, exon 3 and partial intron 3 (227 bp), exon 5 and partial intron 4 (366 bp) were undertaken using custom-synthesised primers. The 366 bp region was genotyped using Single Strand Conformation Polymorphism. The 227 bp region was genotyped using DNA pooling assay to yield a 139 bp product for subsequent High-Resolution Melting analysis. The association of dGH genotypic variants for these loci with fortnightly body weight at pre-pullet stages up to 16 weeks of age was analysed. Result: In the 366 bp fragment, GG and GA genotypes were revealed with one novel SNP (g 74G greater than A). The GG homozygotes had significantly higher body weight at all stages from two to 14 weeks of age (p≤0.01). A novel SNP (g 71A greater than G) was revealed at the 139 bp locus within the 227 bp region with three genotypes viz., AA, AG and GG. The GG homozygotes had significantly higher body weight at six, 14 and 16 weeks of age (p≤0.05). The study revealed that dGH polymorphic loci have jointly contributed to the variation in growth and hence can be used as markers for the primary selection of growers at sixth week of age followed by their secondary selection at 14-16 weeks of age during the multi-stage selection programmes for breeder ducks.