Optimizing embryo growth and broiler chick performance under thermal stress: The role of thyme and peppermint extracts in enhancing health and survival.

This study investigated the effects of thyme and peppermint extract sprays on eggs, emphasizing their antioxidant properties and impact on poultry embryo growth. Key evaluated traits included embryonic quality, hatchling metrics, yolk sac residue, intestinal morphology, and broiler performance during the first week, alongside blood stress indicators. A 5 × 2 factorial experiment was conducted on 1500 eggs treated with ascorbic acid, peppermint extract, thyme extract, distilled water, or no spray, under both normal and heat stress conditions. The results revealed that thyme and peppermint sprays significantly increased egg weight and reduced water loss. Peppermint extract increased yolk sac weight on day 18 (P < 0.05), while thyme extract decreased embryonic mortality under normal temperatures. However, peppermint extract and ascorbic acid negatively affected mortality and incubation time, respectively (P < 0.05). Thyme extract reduced the yolk sac-to-chick weight ratio in hatched chicks under normal conditions. Under heat stress, untreated chicks had higher body surface temperatures compared to those treated with ascorbic acid (P < 0.05). Thyme extract reduced cortisol levels and white blood cell counts under heat stress compared to peppermint extract (P < 0.05). Thyme extract also improved intestinal morphology in heat-stressed chicks, increasing villus height and the villus-to-crypt depth ratio. Peppermint under heat stress and ascorbic acid under normal conditions increased crypt depth, while ascorbic acid under heat stress improved villus width. Thyme extract additionally increased goblet cell numbers compared to distilled water (P < 0.05). Forty-eight hours post-hatch, heat stress elevated chicks' body temperatures, while thyme extract sprays significantly reduced them (P < 0.05). Chicks sprayed with distilled water under heat stress showed the highest weight gain. In conclusion, thyme extract spray is an effective intervention for improving hatchability, yolk sac absorption, intestinal morphology, and reducing cortisol levels under heat stress, offering practical applications for enhancing poultry production efficiency and health.