Malheiros, R. D.Moraes, V. M. B.Furlan, R. L.Bruggeman, V.Buyse, J.Decuypere, E.Macari, Marcos [UNESP]2014-05-202014-05-202002-01-01Acta Veterinaria Hungarica. Budapest: Akademiai Kiado, v. 50, n. 4, p. 425-434, 2002.0236-6290http://hdl.handle.net/11449/2655Somatotrophic and thyroid hormones were determined around the onset of reproduction in broiler breeders reared in two different housing systems [dark, close-sided house (CH) and conventional, open-sided house (OH)]. In both groups age-related changes were obvious for thyroxine (T-4), growth hormone (GH) and insulin-like growth factor (IGF-1); levels of T-4 decreased, especially between 24 and 28 weeks in both groups; concomitantly GH sharply increased over the same period. A transient peak in triiodothyronine (T-3) occurred between 25 and 27 weeks. The effect of housing was only present after the onset of lay. Between weeks 27-28 and the end of the period studied, the CH group showed higher levels of GH and T-3 but lower T-4 levels as compared to the OH group. A significant increase in GH after onset of lay, without any significant rise in T-3 or in IGF-I, could point to a relative insensitivity to high plasma GH levels. Changes at GH receptor level, together with an increased pituitary GH secretion and/or decreased GH turnover may be expected. This may indicate that hypothalamo-pituitary changes at the onset of lay not only imply changes of gonadotrophic cell function, but also other hormonal axes. The relatively decrease in T-4 without changes in T-3, may point to a decrease in the activity of the thyrotropic axis.425-434engHormonesbroiler breedersreproductionEnvironmentGrowth hormonethyroid hormonesArtigo10.1556/AVet.50.2002.4.5WOS:000179714100005Acesso restrito571355857292666908064094841596420000-0001-9549-0329