Developmental programming in chickens including transgenerational nutrition, chemosensory mechanisms and in ovo essential oils, organic acids, and pre- pro- syn-biotics; role of epigenetic modifications

The post-hatching period in chickens is marked by the transition in nutrient source from the endogenous liquid yolk to exogenous solid feed, and the vulnerability to environmental pathogens underscoring the importance of an early development of the digestive and immune systems. This review explores innovative strategies to address these challenges, including developmental programming through broiler breeder interventions, and in ovo applications. Developmental programming mechanisms evolved as evolutionary strategies to optimize the survival of future generations in anticipation of environmental challenges including nutritional scarcity. These may involve chemosensory pathways influenced by dietary volatile compounds (VOCs) becoming one of the main factors determining feeding behaviour and appetite immediately after hatch. Dietary VOCs are transferred from the breeder diet to the fertile egg, shaping innate food preferences in the next generation. Other plant functional compounds include essential oils (EO) which are also partially transferable to the developing embryo with functional activities relevant to gut health in chickens. Carvacrol (the main active compound in oregano EO) can be supplemented through breeder diets to influence embryonic development. A systematic study on in ovo applications of EO identified compounds enhancing embryonic growth and the development of the digestive and immune systems. Changes in the pH of egg compartments (particularly albumen and yolk) respond to the metabolism of the developing embryo. These compartments show a high buffering capacity required for a tight control of the pH. The in ovo application of organic acids has the potential of changing compartmental pH and modulate enzymatic activities. Thus, it is possible to control nutrient release by controlling pH dynamics. Several of the environmental effects on developmental biology involve epigenetic mechanisms. A review of current epigenetic modifications relevant to chicken embryonic and post-hatch development has been outlined. In summary, this review highlights trans- or inter-generational mechanisms and novel in ovo strategies that have the potential to improve post-hatch robustness in chickens.