Polymorphisms in GH, GHR, PRL, and IGF-1 genes and their associations with growth, carcass, and reproductive traits in chickens: a systematic review

Background Growth, carcass composition and reproductive performance are economically important traits in chickens. Polymorphisms in the genes encoding growth hormone ( GH ), its receptor ( GHR ) and insulin-like growth factor-1 ( IGF-1 ), and prolactin ( PRL ), which regulates incubation behaviour and egg laying, have been associated with these traits, with inconsistent findings across breeds. This review evaluated the consistency of these associations and their potential use in genetic improvement. Methods Scopus and Web of Science were searched for studies published between January 2013 and August 2026. Studies reporting associations between polymorphisms in the four genes and growth, carcass or reproductive traits in chickens were included. Data were extracted in a standardised form, reporting completeness was assessed against eight core data elements, and associations were synthesised by vote-counting, distinguishing replication within a study from replication across independent studies. Study characteristics were examined with a co-occurrence network analysis using the Louvain community-detection algorithm. Results Thirty-eight English-language studies were included, most from Asia, Africa and the Middle East, and more than half examined indigenous breeds. Polymerase chain reaction–restriction fragment length polymorphism genotyping was used in 22 studies. The co-occurrence analysis grouped the literature into a growth-oriented community ( GH , GHR and IGF-1 ) and a reproduction-oriented community ( PRL ). Reporting completeness of the core data required for synthesis was high, although Hardy–Weinberg equilibrium testing, covariate adjustment and effect sizes were reported less consistently. The PRL promoter 24-bp insertion/deletion and the g.2402 C > T polymorphism were most often significant for reproductive traits, and IGF-1 variants in the 5′ untranslated region were associated with growth in three of the four studies that tested them, and promoter variants less consistently. Only two locus–trait combinations were significant in more than one independent study. Evidence for GH was spread across many loci and traits, and evidence for GHR was limited. Conclusions Several PRL and IGF-1 regulatory variants were the most frequently significant candidates and warrant further study, but few studies reported the effect sizes, baseline performance or independent validation needed to support marker-assisted selection. Once validated, these variants may be most useful as prior biological information in genomic selection models, particularly for indigenous breeds.