Effects of commercial genetic selection on gene expression in the developing neuroendocrine system of broilers.

Selective breeding of broilers has significantly improved growth rates, muscle mass, and feed efficiency and may have influenced the neuroendocrine systems that regulate growth and metabolism. Embryonic development represents one-third of the life of a modern broiler. To assess the impact of genetic selection on the neuroendocrine regulation of growth and metabolism during embryonic development, we examined mRNA expression of growth-related genes in the hypothalamus and anterior pituitary of two chicken breeds: the modern Ross 708 broiler and the Athens Canadian Random Bred (ACRB) line, the oldest established strain for meat-type chickens. Hypothalami and pituitary glands were dissected from embryos at days 10, 12, 14, 16, and 18 of incubation (n = 4 for each combination of breed, age, and gender). Levels of mRNA for each target gene were quantified using reverse transcription-quantitative PCR. In the adrenocorticotropic axis, pituitary corticotropin-releasing hormone receptor 1 mRNA levels were influenced by the interaction of breed, age, and gender (P < 0.05). In the thyrotropic axis, pituitary thyroid-stimulating hormone β-subunit mRNA levels were affected by the interaction of breed, age, and gender (P < 0.05). In the somatotropic axis, mRNA levels of hypothalamic somatostatin were higher in ACRB than Ross, whereas overall pituitary growth hormone mRNA levels were greater in Ross than ACRB (P < 0.05). Pituitary growth hormone-releasing hormone receptor 2 and pituitary adenylate cyclase-activating polypeptide receptor 1 were influenced by the interaction between breed and age (P < 0.05). In the gonadotropic axis, hypothalamic gonadotropin-releasing hormone 1 and gonadotropin-inhibiting hormone were influenced by breed, age, and gender, while mRNA levels of pituitary follicle-stimulating hormone β-subunit were affected by the interaction between breed and age (P < 0.05). Hypothalamic agouti-related peptide, neuropeptide Y, and proopiomelanocortin mRNA levels were higher in ACRB than Ross in females (P < 0.05). These findings indicate that genetic selection of broilers has altered the adrenocorticotropic, somatotropic, thyrotropic, and gonadotropic axes, as well as hypothalamic control of appetite and metabolism during embryonic development.