Enayat Rahmatnejad

This study evaluates the effects of early post-hatch thermal manipulation (TM; exposure to 36-38°C for 24 hours on day 3 post-hatch) and dietary fat supplementation on broiler chickens subjected to chronic heat stress (CHS; 34 ± 2°C, 6 hours/day) during the finisher phase (days 28 to 42). A total of 240 one-day-old male Ross 308 chicks were randomly assigned to control or TM groups, receiving the same diet until day 28. At finisher phase, chicks were divided into four treatments: control (basal diet), dietary fat supplementation (4% blend of poultry fat and soybean oil, DF), TM with basal diet (TM), and TM with fat supplementation (TMDF). All groups were exposed to CHS during finisher period. Before CHS, no significant differences in performance or mortality were observed. During the first week of CHS, all treatments showed numerical improvements in body weight gain (BWG) and feed conversion ratio (FCR) compared to the control, with TMDF showing a significant effect. TMDF maintained significantly higher BWG and lower FCR over the entire CHS period (days 29–42). The TM and TMDF groups showed significantly better European production efficiency index (EPEI) and lower mortality compared to the control group. The relative weights of abdominal fat and heart, along with plasma T3 and T4 levels, were significantly lower in the TM and TMDF groups compared to the others. These results suggest that early post-hatch TM combined with dietary fat supplementation effectively alleviates the adverse impacts CHS on broiler performance during the finisher period.