Submitted to: Turkey Technical Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: October 15, 1996
Publication Date: N/A
Interpretive Summary: Because of its short developmental period and accessibility of the embryo, the incubated egg has been the object of numerous embryological studies. Yet, despite the possible huge economic benefits which would result from improving the number of eggs hatching, almost nothing is known about the relationships between embryo development and egg handling and storage procedures on the commercial farm or hatchery. This review provides an overview of the events which may impact on the successful development of the embryo. This information is useful to scientists as well as hatchery technicians attempting to identify whether the embryo is dead, viable, or the egg was not fertilized.
Technical Abstract: Neural pathways within the avian brain responsible for initiating gonadal development are not fully understood. A key environmental manipulation utilized to examine altered hypothalamo-pituitary function during sexual maturation is the photoperiod. Another manipulation that will help elucidate neuroendocrine systems involved in puberty is the use of sulfamethazine (SMZ). Both SMZ feeding and photostimulation appear to involve the central nervous system. Within two days of consuming SMZ mixed in a standard starter ration, broiler males show significantly elevated plasma luteinizing hormone levels (p </= 0.05) that remain higher than controls for several weeks. Plasma T3 levels, in contrast, are slightly but significantly lower only during the first six days following SMZ intake. Within two weeks of chronic feeding of SMZ, gonads are significantly larger compared to controls. However, the progonadal effect can be blocked by adding 0.5ppm T3 to the diet. Within the brain, two significant changes occur to thyroid releasing hormone (TRH) and neuropeptide Y (NPY) containing neurons. TRH-like ir within the median eminence (ME) is greater in experimentals. NPY-like neurons within the inferior hypothalamic nucleus (IHn), infundibular n. (IN) and internal zone of the ME are significantly more numerous and show a greater number of darker ir neurons in SMZ-fed chicks versus controls. Results suggest that early sexual maturation in chicks may be characterized by a transient reduction in plasma T3 and an activation of NPY-like neurons in the IH, IN and ME.