The chicken hatching egg is a self-contained life-supporting system for the developing embryo. However, the post-hatch performance of birds depends on several factors, including the breeder management and age, egg storage conditions and duration before incubation, and the incubation conditions. Studies have determined the effect of incubation factors on chick post-hatch growth potential. Therefore, chick physical quality at hatch is receiving increasing attention. Indeed, although incubation temperature, humidity, turning and ventilation are widely investigated, the effects of several variables such as exposure of the embryo to high or low levels, time of exposure, the amplitude of variations and stage exposures on embryo development and post-hatch performance remain poorly understood. This review paper focuses on chick quality and post-hatch performance as affected by incubation conditions. Also, chick physical quality parameters are discussed in the context of the parameters for determining chick quality and the factors that may affect it. These include incubation factors such as relative humidity, temperature, turning requirements, ventilation, in ovo feeding and delay in feed access. All these factors affect chick embryo physiology and development trajectory and consequently the quality of the hatched chicks and post-hatch performance. The potential application of adapted incubation conditions for improvement of post-hatch performance up to slaughter age is also discussed. It is concluded that incubation conditions affect embryo parameters and consequently post-hatch growth differentially according to exposure time and stage of exposure. Therefore, classical physical conditions are required to improve hatchability, chick quality and post-hatch growth.

Heat stress induces economics losses in poultry production. Several studies have shown that this negative effect can be reduced by heat treatments like thermal manipulation during incubation (TMI) and early age thermal conditioning (ETC). The aim of this study was to investigate the effects of TMI on embryo development and the effects of TMI and ETC on productive performances of broilers under a tropical climate. The study involved 1000 Ross 308 broiler hatching eggs incubated at standard incubation conditions (37.8°C at 60% relative humidity = RH) until embryonic day (E) 7. Then the eggs were divided into two groups: a control group (Ci) incubated at standard conditions until hatch and a treatment group (Ti) subjected to TMI (39.5°C at 65% RH) for 12 h/d from E7 to 16. Chicks were assigned to one of two treatments at 3 days of age: chicks from the Ci group were assigned to CiP0 (chicks from eggs incubated normally and reared without ETC) and CiP1 (chicks from eggs incubated normally but exposed to ETC). Chicks from the Ti group were allocated to TiP0 (chicks from incubation with TMI and reared without ETC) and TiP1 (chicks from incubation with TMI and exposed to ETC). Microclimatic data (temperature 22 -34°C and 58-70% RH) were recorded. Results indicated higher (p˂0.001, p = 0.002) hatchability and chick quality in the Ci group. Final body weight was influenced by TMI and ETC. Feed conversion and feed intake were reduced by TMI, but not by ETC, which had an effect on mortality rate. A significant effect of TMI × ETC was observed on daily weight gain and mortality rate. In conclusion, ETC had a good and lasting impact on growth and survival and TMI improved FCR of broilers under a chronic hot environment. ETC plus TMI adversely impacted growth but improved survivability of broiler chickens.

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