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PubMed2026

Research note: Genetic background influences the relationship between age at first egg and long-term egg production in layers.

Age at first egg (AFE) is a key selection criterion in layers breeding. With the laying cycle being extended to 100 weeks, the relationship between AFE and long-term productivity and egg quality should be evaluated to ensure that selection for AFE aligns with current breeding objectives. In this study, Beijing-You chickens and White Leghorns were used to generate purebreds and crossbreds. Egg-laying performance was recorded including AFE, egg number and cumulative egg number at different stages from onset till 100 weeks, and egg quality traits at 32, 54, 72, 86, and 100 weeks. Genetic correlations were estimated, both in the combined population of purebreds and crossbreds and within each genetic group. In the combined population, a positive genetic correlation was observed between AFE and cumulative egg number till 100 weeks. Age-dependent genetic correlations between egg number at different stages and AFE further revealed that extremely early-maturing hens showed initial production advantages, but these advantages diminished at later stages. Importantly, the genetic and phenotypic correlations between AFE and egg quality traits were weak, with correlation coefficients ranging from -0.18 to 0.35. Within each genetic group, the relationships between AFE and egg production also showed consistent age-dependent patterns. For the long-term production targets, optimal AFE seems to differ by genetic backgrounds. White Leghorns showed higher egg production with earlier maturity, whereas in Beijing-You chickens, maintaining AFE at approximately 140-189 days appeared to be more favorable. Overall, these findings demonstrated that earlier AFE does not ensure higher egg production at extended laying cycles and has negligible influence on egg quality, highlighting the importance of optimizing AFE according to genetic background.

Age at first egg↗

PubMed2026

Age-associated chromatin repression of Hippo-Yap signaling drives oogonial stem cell decline in chicken.

Oogonial stem cells (OSCs) are a type of reproductive germline stem cell present in the ovaries of adult animals after birth. They have been proposed to contribute to follicle renewal and could be associated with reproductive longevity, yet the molecular mechanism contribute to OSC malfunction during aging in chicken remain unclear. Here, we show that OSC number and proliferative capacity decline significantly from pre-laying to late-laying stages, accompanied by increased follicular atresia. RNA-seq analysis revealed a global reduction in transcriptional activity in aged OSCs. ChIP-seq demonstrated elevated H3K27me3 deposition, particularly at promoter regions, which correlated with repression of proliferation-related genes in the Hippo pathway including YAP1 and TEAD1. Pharmacological inhibition of H3K27me3 reduced repressive chromatin marks, restored Hippo pathway gene expression, and significantly enhanced OSC proliferation. Conversely, YAP1 knockdown attenuated proliferation-associated gene expression. These findings indicate that age-dependent H3K27me3 accumulation suppresses OSC proliferation through epigenetic repression of the Hippo-YAP axis, providing mechanistic insight into ovarian aging and a potential strategy to extend the laying cycle in poultry.

Animals↗

PubMed2026

The current and future perspective of ChickenGTEx project and its applications in precision breeding.

The Chicken Genotype-Tissue Expression (ChickenGTEx) project was established to systematically characterize the regulatory landscape of the chicken genome and to accelerate the translation of functional genomics into precision breeding. By integrating whole-genome sequencing with multi-tissue transcriptomic profiling, ChickenGTEx provides a comprehensive atlas of gene expression regulation across diverse tissues and physiological systems. Current findings demonstrate that complex production traits are governed by coordinated regulatory networks rather than isolated loci, with substantial contributions from tissue-specific gene expression, structural variation, and genotype-by-sex interactions. Sex-dependent regulatory effects further refine the genetic architecture of metabolic, immune, and reproductive traits, highlighting the importance of incorporating sex as a biological variable in genomic analyses. Application of integrative omics frameworks within elite layer populations has revealed multilayer regulatory mechanisms underlying extended laying performance, feed efficiency, metabolic health, and eggshell quality. By partitioning phenotypic variance into genetic, regulatory, and host-microbiome components, these approaches move beyond association-based mapping toward causal inference and biological interpretation. Importantly, validated regulatory loci identified through ChickenGTEx and related analyses provide actionable markers for genomic selection and rational targets for precision genome modification. Looking forward, continued expansion of regulatory atlases, incorporation of single-cell and longitudinal data in diverse environmental conditions, and integration of functional annotation into breeding pipelines will further enhance prediction accuracy and sustainable genetic improvement. The ChickenGTEx project thus represents a foundational platform bridging functional genomics and practical poultry breeding.

Animals↗

PubMed1976

Selection for body weight at eight weeks of age. 11. Ovulation and oviposition patterns.

Two experiments were conducted to study oviposition patterns and ovarian activity at various physiological ages in S15 and S16 generation pullets from lines selected bidirectionally for high (HWS) and low (LWS) juvenile body weight. The fixed periods of lay for random samples of pullets from the date of first egg were 20, 40, 60, and 80 days in the first experiment and 40, 80, 120, and 160 days in the second experiment. HWS pullets matured significantly earlier than LWS pullets in both generations. The frequency and the percentage hen-day production (%HDP) of defective eggs were significantly greater in the HWS than LWS line in both generations. Delayed sexual maturity did not significantly change the pattern of defective egg production for a fixed period of lay. In the HWS line the %HDP of defective eggs progressively increased until about 40 days of lay and tended to decline thereafter, while in the LWS line the percentage decreased from 20 to 40 days and then stabilized. The frequency of normal unbroken eggs to 80 days of production did not differ among lines either in the S15 or S16 generation. When measurements were extended to 160 days of lay in the S16 generation HWS pullets produced significantly more normal eggs than LWS pullets. Possible effects of ovarian activity on the egg production pattern during the laying cycle are discussed. There was a significantly higher incidence of internal laying and atrecia of the growing follicles in the HWS than in the LWS pullets. Ovarian activity, evidenced by the number of developing and ruptured follicles, was significantly greater in the HWS than the LWS line, as was the incidence of ova developing in pairs. Product moment correlations and multiple regressions among the measurements of ovarian activity were calculated within lines. In the HWS line, 62.5% of the variation in %HDP of defective eggs could be accounted for by the %HDP of normal eggs and the number of developing follicles while in the LWS line these variables accounted for only 7.29% of the variation in %HDP of defective eggs.

Age Factors↗