Effects of Thermal Stimulation Duration During Incubation on Organ Development and Tona Scores of Chicken Hatchlings

Global warming and rising ambient temperatures pose a significant threat to poultry production, underscoring the urgent need for adaptive strategies. Thermal stimulation during incubation has been proposed as a method to enhance thermotolerance in chickens. However, the safe duration of thermal stimulation that maintains normal embryonic development and chick quality remains uncertain. This study evaluated the effects of different durations of thermal stimulation on organ development and Tona scores in chicken hatchlings. A total of 200 fertile eggs were randomly assigned to four treatments with five replicates of 10 eggs each. Treatments consisted of standard incubation for 21 days (T0, control) or daily thermal stimulation from embryonic day 10 to 18 for 2 hours (T1), 4 hours (T2), or 6 hours (T3). Chicks were removed from the incubator at 516 hours of incubation, and organ development and Tona scores were assessed. Results indicated that organ weight and relative percentages of the heart, liver, and gizzard were not significantly influenced by any treatment. Thermal stimulation up to 4 hours/day did not significantly affect down and appearance, retracted yolk, eyes, legs, navel area, remaining membrane, remaining yolk, or overall Tona scores. However, thermal stimulation for 6 hours/day significantly reduced the activity score. In conclusion, thermal stimulation for up to 4 hours/day during embryonic days 10 to 18 can be considered a safe threshold, whereas longer exposure may compromise chick activity. These findings provide practical insights for managing incubation practices as a potential adaptation strategy for poultry production under changing climatic conditions.