Meta-analysis of Genetic Parameters for Productive and Reproductive Traits in Laying Hens

Background: In poultry breeding, reliable genetic parameters for economic traits are necessary to develop breeding programs.However, estimated genetic parameters in studies with small sample sizes are associated with large standard errors.Therefore, it is recommended to combine the obtained estimates from different studies to increase the reliability of genetic parameters.A meta-analysis is a statistical analysis that combines the results of several scientific studies.The advantages of meta-analysis studies in poultry breeding are high statistical power, ability to extract more information about poultry population, evaluation of the effects in different subgroups of poultry population, and overcoming on limitations of small sample size.Proper use of metaanalysis method in studies related to livestock and poultry prevents the repetition of unnecessary work and it saves time and reduces costs.Considering the importance of estimation of genetic parameters for productive and reproductive traits in laying hens and the fact that no comprehensive systematic review and meta-analysis has been performed to investigate the genetic parameters in this species, the goal of this study is to use meta-analysis for estimation of weighted mean of genetic parameters for desired traits through combining the results of different studies.Methods In this study, data collection was performed from international and Persian databases including Google scholar, Scopus, Web of Science, PubMed, Science direct, Magiran, Irandoc, SID.The search process in the mentioned databases was performed using the keywords including genetics, phenotype, heritability, correlation, reproductive traits, sexual maturity, egg number, egg weight, laying hen and their possible combination.At first, the studies that were repeated in different databases were deleted from study.Then, the titles list of all remaining articles was prepared.In the first stage, i.e. screening, the title and abstract of remaining articles were carefully studied and unrelated articles were deleted.In the second stage, i.e. evaluation of studies, the full text of related articles remaining from the screening stage were investigated.From search of different databases, 152 articles were obtained and finally 33 articles between 1984 and 2022 were used in analysis and 119 articles were excluded.Meta-analysis of genetic parameters for egg production and maturation traits in laying hens was performed by agregating the results of 33 articles.The I 2 index showed that the heterogeneity in all investigated traits for heritability and genetic and phenotypic correlations was more than 70%, so random effects model was used for data analysis.The software package Comprehensive Meta-Analysis (version 2) was used to perform statistical analysis and estimation of weighted means of heritability and genetic and phenotypic correlations for sexual maturity age, sexual maturity weight, egg number and egg weight, standard error and 95% confidence interval.Results: Based on results, the highest weighted mean of heritability is for egg weight (0.49), and then for the sexual maturity weight (0.31), and the lowest heritability was for egg number (0.29).The highest positive weighted mean of genetic correlations was between sexual maturity weight and egg weight (0.53) and then between sexual maturity age and sexual maturity weight (0.31), also the highest negative genetic correlation was between egg number and egg weight (-0.36) and then between sexual maturity age and egg number (-0.25).The highest positive weighted mean of phenotypic correlations was between sexual maturity weight and egg weight traits (0.24) and then between sexual maturity age and sexual maturity weight traits (0.19).As well as the highest negative phenotypic correlations was between egg number and egg weight (-0.18) and then between sexual maturity age and egg number (-0.16).Comparing of obtained 95% confidence