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.

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Manihot esculenta leaf meal in feed at post-hatch improves growth and egg production. One may question the efficacy of Manihot esculenta leaf extract for in ovo feeding. This study was conducted to determine the effects of in ovo injection of Manihot esculenta extract on hatchability, growth performance and biochemical parameters of Sasso broiler chickens. The hatching eggs from 38-week-old broiler breeders were set and at d 18 of incubation, 600 eggs with evidence of living embryos were assigned to 4 treatment groups of 150 eggs each. These groups were: (1) eggs without in ovo injection (negative control); (2) eggs perforated but no injection of any additive (positive control); (3) eggs perforated and injected with 0.1 ml of saline solution and (4) eggs perforated and injected with 0.1 ml of Manihot esculenta extract. Data were collected on hatching performance. During the post hatch growth phase, performance traits such as feed intake, weight gain, and feed conversion ratio were collected and at 84 days of age, blood samples were taken for determination of serum total proteins, triglycerides, aspartate aminotransferase (ASAT) and alanine amino transaminase (ALAT). The results showed that hatchability was similar in the negative control and Manihot esculenta extract groups but significantly higher (P < 0.05) than those of positive control and saline solution treatment groups. Chick quality was better in the groups with Manihot esculenta extract and saline solution application. Post-hatch, the body weight gain of birds from the Manihot esculenta extract group was higher than those in the groups with saline solution application and in the negative control and positive control groups.Manihot esculenta leaf extract increased significantly the triglyceride rate and reduced ALAT and ASAT concentration at hatch. It can be concluded that in ovo inoculation of 0.5 μg/ml Manihot esculenta leaf extract on d 18 of incubation into the eggs air chamber improved hatchability, chick quality and post-hatch growth of broilers.