ABSTRACT Due to its central position in the production chain, in-ovo development is influenced by pre-incubation factors that affect the quality of embryonated eggs and incubation conditions themselves, and both may influence egg hatchability and chick quality, as well as bird survival, growth performance, and phenotype in the field. The evolution of the incubation process over the years is characterized by significant scientific and technological development. Presently, the main current focuses of research are the manipulation of thermal incubation conditions, eggshell temperature, and the integrated effects of factors that influence incubation. In this context, one of the questions that needs to be asked is how effective are the current physical conditions of incubation to promote greater hatchability and better quality chicks, and higher survival and better performance in the field under adverse conditions or not. What are the new and future prospects for incubation? The purpose of this paper was to review the role of the physical agents of incubation, such as temperature, relative humidity, O2 and CO2 concentration, and egg turning and position from an integrated perspective, considering egg incubation as the transitional link between egg and poultry production.

An experiment was carried out with 1200 23-week-old white Dekalb commercial laying hens to investigate production responses, egg quality, and energy utilization of laying hens fed different dietary energy levels at the beginning of lay. Birds were housed and divided in five groups of 240 birds according to dietary apparent metabolizable energy corrected for nitrogen (AMEn): 2700 kcal/kg; 2775 kcal/kg; 2850 kcal/kg; 2925 kcal/kg; and 3000 kcal/kg, with six replicates of 40 birds each. Birds were fed the experimental diets based on corn and soybean meal for 17 weeks. Diets were iso-nutritive, except for energy level. Increasing AMEn levels had a negative effect on egg production and egg mass (p≤0.05). AMEn levels did not influence body weight, egg weight, or livability (p>0.05). Increasing AMEn levels increased (p≤0.05) feed intake and AMEn conversion ratio and feed conversion ratio. AMEn intake remained constant, independently of dietary AMEn level (p>0.05). There were no differences in albumen height, yolk total solids content, or egg component percentages (p>0.05). Egg specific weight improved with increasing AMEn levels (p≤0.05). Therefore, the energy level of 2700 kcal/kg of feed may be fed to young laying hens.