Involvement of the hypothalamic-pituitary-thyroid axis and its interaction with the hypothalamic-pituitary-adrenal axis in the ontogeny of avian thermoregulation: a review

The emergence of thermoregulation in avian species is a complex matter in which neural as well as hormonal processes are involved. In a previous paper, the neural aspects of primary avian thermoregulation were discussed. In this paper the role of the hypothalamus-pituitary-thyroid axis (HPT-axis) and the hypothalamus-pituitary-adrenal axis (HPA-axis) in the ontogeny of avian thermoregulation is evaluated. The regulatory mechanisms and different important hormones of both axes, which have stimulatory or inhibitory effects, are discussed. Because the onset of functionality of the thermoregulatory system is of great interest, the ontogeny and functionality of the hormonal axes are clarified. There is a great difference between precocial and altricial birds in hormonal events as well as in neural processes which are involved in the emergence of thermoregulation. In precocial avian species the HPT-axis becomes functional during the mid- to late embryonic period while the same axis only becomes fully functional during the first week post-hatch in altricial avian species. As early as the sixties, the emergence of homeothermy in chickens was investigated. It was concluded that the thyroid gland plays an important role in the thermoregulatory mechanisms of newly hatched chicks. More recent studies however were not able to show any direct effect of the thyroid hormones on the thermoregulation of day-old chicks, although blocking the conversion of T4 to T3 caused a decrease in body temperature in young chicks. Thyrotropin releasing hormone (TRH) is known to act in thermoregulation in mammals and several authors have found an effect of TRH on the metabolism of young and older chicks. However, the exact mechanism still remains unclear. Because the HPT- and the HPA-axis show close relationships, the role of the HPA-axis in the ontogeny of thermoregulation is also taken into consideration in this review. In mammals as well as in birds, corticotropin releasing hormone (CRH) is involved in the primary thermoregulation. We conclude that the HPT-axis has an important role in the ontogeny of avian thermoregulation. The exact role of the HPA-axis remains largely unclear although at least CRH is definitely of some importance

Effecten van temperatuur tijdens incubatie op postnatale groei

De voorwaarden voor en tijdens het incuberen in geventileerde broeikasten met homogene temperatuurverdeling liggen sinds geruime tijd vast en onveranderd en werden tot nog toe niet in vraag gesteld. Nochtans rezen er nieuwe vragen, nieuwe feiten en twijfel op

Physiological studies on the sex-linked dwarfism of the fowl: a review on the search for the gene's primary effect

International audienc

Niveaux hormonaux plasmatiques de poules albinos (sal-c) et non albinos (S)

Des poules albinos (mutation s al-c) et non-albinos (colorées) de même origine ont été comparées pour des niveaux plasmatiques hormonaux, triiodothyronine (T3), thyroxine (T4), hormone de croissance (GH) et corticostérone, avant l’entrée en ponte puis après 3 à 4 mois de ponte. Le rapport T3/T4 était plus élevé chez les poules albinos que chez les non-albinos aux 2 âges; cette différence s’approche de la signification après l’entrée en ponte. La variance intra-génotype de ce rapport est plus élevée pour les poules s al-c que pour les non-albinos (P < 0,01). D’autre part, le taux de l’hormone de croissance ne diffère pas entre génotypes avant l’entrée en ponte, mais en période de ponte il est significativement plus élevé chez les poules s al. Il existe donc certaines différences dans l’équilibre hormonal des 2 génotypes. On peut espérer que ceci aide à l’interprétation des effets trouvés associés au gène albinos sur la production d’oeufs.Albino (s al-c) and non-albino (colored) hens from the same origin were compared for several plasmatic hormonal levels (triiodothyronine (T3), thyroxine (T4), growth hormone (GH), and corticosterone) before the onset of laying and after 3-4 months of production. The T3/T4 ratio was higher among albino than among non-albino females at the 2 ages; this difference approached significance after sexuaL maturity. The within-genotype variance of this ratio was higher for s al-c hens than for non-albino ones (P<0.01). On the other hand, the GH level did not differ between the 2 genotypes before the onset of laying, but during laying it was significantly higher for the s al-c females. There are therefore some differences in the general hormonal balance of the 2 genotypes. It is hoped that this may help in an interpretation of the effects on egg production associated with the albino gene

Higher levels of CO2 during late incubation alter the hatch time of chicken embryos

status: publishe

Gas exchange during storage and incubation of Avian eggs: Effects on embryogenesis, hatchability, chick quality and post-hatch growth

Embryonic development is a dynamic process that requires a fine balance between several factors in order to achieve an optimum hatchability and chick quality. These factors include the background of the embryo, such as genetic line of the breeders, the age of the breeder, egg weight, and factors related to the environment in which the egg is stored and incubated, such as temperature, humidity, gas levels and altitude. Gas exchanges are of fundamental importance for embryonic development during incubation and may affect the livability of the embryo. This paper reviews the roles of the gaseous environment (i.e. O 2 and CO2) around hatching eggs during storage and during incubation and the effect it might have on the survival of the developing embryos and the chicks that hatch. The state of the art on the different attempts to establish the optimum requirements of different gases that promote the optimal developmental trajectories at different periods during incubation is presented. The roles and consequences of different levels of O2 and CO2 during storage and incubation on hatchability, incubation duration, hatching process, embryo growth, embryo mortality, organ development and morphology, metabolism, blood acid-base balance, chick quality and chick post-hatch growth are reviewed. © 2007 World's Poultry Science Association