Effects of embryo thermal manipulation on thermotolerance of broiler chicks between 28–40 days of rearing

This study examined the impact of a 37.5 °C temperature on chick embryos during the hatching period (18–21 days of incubation) and its subsequent effect on hatchery results and the thermotolerance of broiler chicks from 28–40 days of rearing. For hatchery results, the study involved 16 trays per treatment. For performance, the study involved 360 broiler chicks from two distinct hatching temperature conditions: a control group (36.5 °C and 65% relative humidity (RH)) and a thermal manipulation group (37.5 °C/6 h/d from 18 to 21 days of incubation with 65% RH). The chicks were reared in a thermoneutral temperature until day 28. Subsequently, on day 28 post-hatch, the chicks were randomly assigned to a 2 × 2 arrangement to assess the differences in thermotolerance acquisition. The primary factors were embryo thermal manipulation in the hatcher and the thermal environmental rearing from day 28 until day 40 (thermoneutrality (at a constant 23.0 °C) or thermal environmental challenge (30.0 °C/6 h/d)). No effect was observed on hatchability, residual analysis of unhatched eggs, and chick quality. No interaction was observed between treatments for performance or cloacal temperature from day 28 to day 40. However, birds reared in a thermoneutral environment exhibited higher feed intake and body weight gain from day 28 to day 40 and a lower feed conversion ratio than the birds reared in a cyclic heat temperature environment. An increase of 1 °C/6 h/d in the hatcher from day 18–21 does not affect hatchery results or enhance the adaptability of broilers to a heat stress environment during the final rearing period