Strain-specific responses to heat stress: egg quality and oviductal gene expression in laying hens

This study investigated the impact of chronic intermittent heat stress (35 ± 1 °C, 55 ± 5% relative humidity) applied for six hours daily, three days a week, over two months on the external and internal egg quality traits of four-layer hen strains. 176 laying 30–week old hens were utilised, with 44 hens from each of the following breeds: Lohmann Brown (LB), Golden Sabahia (GS), Fayoumi (FY), and White Leghorn (WL). The study also examined the regulation and expression of the GDF9, ovalbumin, HSP70, and OC-17 genes in the magnum, isthmus, and uterus regions of the oviduct. Among the four strains, LB hens exhibited the highest egg weight, length, width, and shape, highlighting the significant influence of genotype (p < 0.05). FY hens demonstrated resistance to heat stress, showing minimal effects from temperature fluctuations. Heat stress significantly impaired eggshell characteristics, resulting in reductions in eggshell weight and thickness by 5.88% and 10%, respectively, and a significant interaction was observed between genotype and heat stress on egg weight, length, and surface area. GDF9 expression was upregulated in the magnum and uterus tissues of LB hens, while HSP70 expression was significantly downregulated in the magnum by 5.34%, likely due to recovery during recess periods, implying a tissue-specific recovery. These findings suggest that heat stress negatively impacts egg quality traits, but its effects on oviductal gene expression vary depending on strain and tissue region.