Ferulic acid supplementation in embryonic eggs improves heat resistance of broilers by optimizing thermal...

Embryonic thermal manipulation (TM) enhances heat tolerance in broilers but often reduces hatchability and impairs chick quality. This study investigated the effects of TM combined with soaking embryonic eggs in ferulic acid (FA) solution on the growth performance and heat resistance of broilers. The objective was to optimize the TM regime and clarify the mechanisms by which FA-pretreated TM affects the heat tolerance in growing broilers exposed to heat stress. A total of 1000 fertilized eggs (57 ± 4 g) were randomly divided into three groups: control, TM and TM+FA (soaked in 120 mg/L FA solution from embryonic days 6 to 8). Broilers in the TM and TM + FA groups underwent thermal manipulation from embryonic day 7 to day 16 (10 days) at 39.5 °C and 65% relative humidity for 18 h daily. After hatching, the chicks were reared under standard conditions until 28 days of age, followed by a 2-week chronic cyclic heat stress challenge (35 ± 2 °C, 8 h/d). The results showed that TM+FA improved the hatchability, decreased serum corticosterone levels and feed-to-gain ratio of 28-day-old broilers, and downregulated the gene expression of thyrotropin-releasing hormone (TRH) in the hypothalamus, decreased body temperature of broilers under heat stress (P < 0.05). Both TM and TM+FA alleviated heat-stress-induced liver injury, as evidenced by enhancing antioxidant capacity and decreasing serum alanine aminotransferase activity, and inhibited cardiomyocyte apoptosis via lowering the Bax/Bcl-2 ratio and decreasing HSP90 gene expression (P < 0.05). In conclusion, soaking TM-treated embryonic eggs in FA solution effectively improves the hatchability and heat tolerance of broilers during the post-hatch growth period. Thus, the TM + FA treatment provides a more reliable approach than the single TM treatment to combating heat stress in poultry production.