Search for genes associated with the age at first egg in laying hens (Gallus gallus L.)

The age of onset egg laying is an important selection trait that is considered when breeding poultry, especially when obtaining highly productive egg crosses. The homogeneity in this parameter of commercial laying hen populations becomes relevant due to synchronization of hens’ productive use and an increase in the overall egg production of the herd. The beginning of egg laying depends on several factors and primarily on the onset of females’ puberty. In poultry, a number of studies, including genome-wide analysis have shown the genetic determination of this trait and identified genetic markers for the time of puberty and the onset of egg production in laying hens. However, this issue still requires further elucidation with regard to peculiarities of species, breeds. crosses, and populations. The aim of the research was to search for single nucleotide polymorphisms (SNPs) and to identify genes associated with the onset of egg production in laying hens (Gallus gallus L.). The studies were conducted on F2 model resource population (n = 95) created by crossing two breeds, the Russian White and White Cornish contrasting in egg productivity (Ernst Federal Research Center for Animal Husbandry, 2023-2024). The poultry of F2 resource population were genotyped using medium density chips Illumina Chicken 60K SNP iSelect BeadChip (Illumina, Inc., USA). To estimate the age of laying onset, the 12-week-old birds were transferred to individual cages to record the laying of the first full-fledged egg. Based on the obtained genotypic and phenotypic data, a GWAS analysis was carried out using PLINK 1.9 software (https://www.cog-genomics.org/plink/). It was found that the laying hens of the resource population were highly variable in the age ar egg laying initiation, the intrapopulation differences reached 58.2 %. Based on the GWAS analysis, eight significant (p -4) SNPs associated with the trait and located on chromosome GGA3 and 60 genes in the regions of the detected SNPs were identified, including four genes, the AIDA , NKAIN2 , LIN9 , and MAP4K3 which coincide with the positions of the revealed SNPs. Our findings can be used in genomic selection for increasing egg productive potential.