In-ovo feeding was examined in-depth to understand how exogenous nutrients could affect embryonic growth and hatching. As a result, the relationship between the initial feeding and post-hatch chick performance is particularly intriguing. It is widely known that the first feeding stimulates a variety of molecular and cellular targets, including enzymes and hormones, which affect general growth and a variety of physiological processes, including the yolk utilization, metabolic level, and gastrointestinal development ( Decuypere and Bruggeman, 2007). It is well known that denying 1-day-old chicks access to nutrition decreases post-hatch growth. The link between the initial feeding and post-hatch chick performance is crucial. In literature, the relationships between physiological parameters and incubation conditions with embryonic development in time are scarce, and a better understanding of these parameters that affect chick quality and post-hatch growth is highly desired. This could have an impact on embryo general growth trajectory and, as a result, flock uniformity. Furthermore, incubation conditions such as temperature, hypoxia (low oxygen), hyperoxia (high oxygen), and hypercapnia (high CO 2) can alter these physiological parameters and influence embryonic development in various ways. The relationship between several physiological parameters such as corticosterone and thyroid hormones balances, heat production and metabolism, and gas exchange (O 2, CO 2) is crucial for the development of embryos and their survival under the incubation process ( Decuypere et al., 1990 Tona et al., 2004). As a result, the endocrine system is absolutely necessary for appropriate embryonic development and hatching success. Physiological changes occur during embryonic development and the hatched day-old chick results in 21 days of development ( Decuypere and Bruggeman, 2007). To reach this goal, it is vital to determine the sources of variable factors as well as the repercussions of these factors for optimal embryonic development and hatching outcomes.

The major goal of farmers is to develop a chick with good hatchability, viability, and post-hatch performance. The growth and metabolism of a 1-day-old chick are mostly determined by processes that occur during embryonic development.

Therefore, classical physical conditions are required to improve hatchability, chick quality and post-hatch growth. It is concluded that incubation conditions affect embryo parameters and consequently post-hatch growth differentially according to exposure time and stage of exposure. The potential application of adapted incubation conditions for improvement of post-hatch performance up to slaughter age is also discussed. All these factors affect chick embryo physiology and development trajectory and consequently the quality of the hatched chicks and post-hatch performance. These include incubation factors such as relative humidity, temperature, turning requirements, ventilation, in ovo feeding and delay in feed access. Also, chick physical quality parameters are discussed in the context of the parameters for determining chick quality and the factors that may affect it. This review paper focuses on chick quality and post-hatch performance as affected by incubation conditions. 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. Therefore, chick physical quality at hatch is receiving increasing attention. Studies have determined the effect of incubation factors on chick post-hatch growth potential. 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. The chicken hatching egg is a self-contained life-supporting system for the developing embryo. 3Department of Animal Physiology, Federal University of Agriculture, Abeokuta, Nigeria.2Institut Togolais de Recherche Agronomique, Lome, Togo.1Centre d’Excellence Régional sur les Sciences Aviaires, University of Lome, Lome, Togo.

Chicken incubator temperature humidity