Background: Sudden death syndrome (SDS) is a metabolic and cardiovascular disorder of fast-growing broilers, associated with rapid growth, physiological stress and cardiac dysfunction. Ryanodine receptor 2 (RYR2) regulates calcium release during cardiac contraction and is therefore a relevant candidate gene for SDS-related cardiovascular risk. This study detected sequence variation in selected RYR2 regions and examined its association with growth and cardiovascular risk indicators in chickens raised in Nigeria. 
 
Methods: One hundred and fifty chickens comprising ross 308, arbor acres and noiler were evaluated for growth traits, body mass index and selected blood-based cardiovascular indicators. Fifteen representative samples, five per breed, were used for DNA extraction, PCR amplification and Sanger sequencing of selected RYR2 exons and flanking regions. Sequences were aligned with the reference chicken RYR2 sequence to identify polymorphisms. 
 
Result: Sequence analysis identified an A/G single nucleotide polymorphism in the flanking region of RYR2 exon 40 at chicken genome position 3:36968262. Arbor Acres and Noiler chickens carried the G allele, while ross 308 chickens carried the A allele. No polymorphism was detected in exon 23, while exon 44 was not successfully sequenced. Ross 308 chickens showed higher body mass index from weeks 1 to 6, whereas most blood-based cardiovascular risk indicators were not significantly different between breed-associated haplotype groups, except high-density lipoprotein. The detected RYR2 flanking-region SNP may serve as a preliminary breed-associated molecular marker, but further validation using larger populations and individual genotyping is required.

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Comparative Sequencing and Detection of Polymorphism in Targeted Regions of Ryanodine Receptor 2 Gene in Fast and Slow Growing Chickens