The avian maternal environment: exploring the physiological mechanisms driving progeny performance

Environmental factors, both positive and negative, experienced by breeder hens during their reproductive life, can have significant influence on the productive efficiency and health of their progeny. This is particularly important considering that commercial chicken meat birds spend a significant proportion of their life in ovo, and alteration to the in ovo environment can permanently 'program' progeny endocrine pathways. The maternal environment is greatly influenced by factors such as nutrition and stress, both of which play a significant role in the chicken meat breeder industry due to feed restriction practices, ranging from 25% to 80% ad libitum intake. The effects of nutrition and stress and their influence on the maternal environment have been extensively investigated in mammalian literature, primarily focusing on the development and function of the hypothalamic-pituitary-adrenal axis (HPA) in offspring including the exposure of the stress hormone cortisol. Disruption of the HPA axis can inadvertently disrupt other important endocrine pathways, involved in growth and metabolism, including the growth hormone-insulin-like growth factor I axis (GH/IGF-I) and the hypothalamic-pituitary-thyroid axis (HPT). The disruption or 'reprogramming' of metabolic endocrine axes through maternal influences has been linked to variations in progeny performance, including growth rate and body composition; however, the underlying physiological mechanisms responsible for these phenotypic differences still remain unclear, especially in poultry. The aim of this review is to assess current industry practices that may influence the maternal (breeder hen) environment, whilst reviewing the concept of developmental programming, and its application to chicken meat production.