Has the intensive genetic selection of commercial layer chickens impacted the control of the reproductive axis

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Over the last 10 years, the research program of Dr. Bedecarrats focused on elucidating the molecular mechanisms controlling reproduction in poultry. More specifically, recent advances resulted in the characterisation of the dual control (stimulatory/inhibitory) of the reproductive axis in chickens. This included identifying the receptors involved in the hypothalamic control of the anterior pituitary gland along with their signaling pathways and intracellular interactions, and characterizing the dynamic changes occurring at the level of the pituitary gonadotropes during a reproductive cycle (switch from a primarily inhibitory to a stimulatory input). More recently, the team of Dr. Bedecarrats has characterized the effect of light wavelength on the activation of the reproductive axis in chickens, and these results have led to the design, development and validation of a spectrum lighting LED bulb for the egg-laying industry. However, while translating basic research into practical applications, we noticed that modern commercial strains of laying hens no longer fully fit the accepted neuroendocrine models describing the activation and regression of the reproductive axis. Thus, it is likely that in an effort to double the number of eggs laid per hen, the intensive genetic selection performed over the last 50 years has altered the normal physiological control of reproduction. This raises a number of questions such as, why do commercial layers tend to mature without proper photostimulation? Why do they display such extended laying persistency? Is there a desynchronization between the circadian rhythm and the ovulatory process? The research highlighted in this proposal will aim at answering these questions by comparing an unselected experimental strain of Leghorn (Smoky Joe) with a Canadian heritage pure lines (Dr. Donald McQueen Shaver, White Leghorn pure line) and modern commercial strains. The approach is to first compare production parameters and relate these to molecular events occurring within the reproductive axis. By identifying the differences between these strains, results will first help us understand the actual mechanisms responsible for the synchronization of ovulation and the persistency of lay, and will show us how and at what level of the axis the intensive genetic selection impacted reproduction. Finally, understanding the shift in physiological processes will help adjust and refine on-farm management procedures to best accommodate these new commercial lines, possibly by further refining lighting systems and body weight management.