Função tireoidiana de potros nascidos de éguas com placentite ascendente induzida experimentalmente

Abstract

The aim of the manuscript 1 was to address the main clinical alterations related to the thyroid gland that affect equine neonates. There were addressed alterations in the thyroid function that occur either due to primary thyroid disease, such as congenital hypothyroidism and thyroid hyperplasia and musculoskeletal deformities (TH-MSD), or due to secundary diseases, such as nonthyroidal illnessess syndrome (NTIS), besides the diagnostic methods and treatment perspectives. The aim of the manuscript 2 was to determine cortisol and thyroid hormone concentrations (total thyroxine: T4; free thyroxine: FT4; total tri-iodothyronine: T3; and free tri- iodothyronine: FT3) in foals born from mares with experimentally-induced ascending placentitis and to determine their association with survival. We hypothesized that (i) foals born to mares with experimentally-induced ascending placentitis will have lower cortisol and thyroid hormone concentrations at birth, (ii) that these endocrine alterations will be associated with mortality, and (iii) that cortisol and thyroid hormone concentrations in the first hours of life will have prognostic value for survival. Twenty-nine pregnant mares and their foals were enrolled in this study. At 300 days of gestation, mares were assigned to a healthy control group (n=5) or were submitted to experimental induction of ascending placentitis (n=24) through intracervical inoculation of Streptococcus equi subsp. zooepidemicus. Medical treatment was initiated 48 h post bacterial inoculation. Foals born to inoculated mares were assigned to Low-risk (n=14) or Sick (n=10) groups based on adaptive behavior, clinical and hematological findings during the first week of life. Foals were also classified as Term (n=13), Dysmature (n=7) or Premature (n=9) according to gestation length and presence of signs of immaturity. Survival rate was recorded until day 60 post-foaling. Six (6/10) foals from the Sick group did not survived, while all foals from Low-risk and Control groups survived. Cortisol and thyroid hormone concentrations were measured immediately after birth (0 h) and at 12, 24, 48 and 168 h of life. Serum cortisol concentrations were lower in Sick compared to Low-risk and Control foals at 0 h. Serum T3 and FT3 concentrations were lower in Sick compared to Control and Lowrisk foals from 0h to 48 h. Serum FT4 concentrations were lower in Sick and Low-risk than in Control foals at 0 h, while Sick foals had lower concentrations than Control and Low-risk foals from 12 h to 168 h. Premature foals had lower serum cortisol (0 h), T3 (0 h to 48 h), FT3 (12 h to 48 h), and FT4 (0 h to 168 h) concentrations compared to Term and Dysmature foals. No differences were found in cortisol and thyroid hormone concentrations between sick survivor and sick non-survivor foals. In conclusion, sick foals delivered by mares with experimentally-induced ascending placentitis had decreased concentrations of T3, FT3 and FT4 that persist for 48 to 168h, which is consistent with euthyroid sick syndrome or nonthyroidal illness syndrome (NTIS). Cortisol and thyroid hormone concentrations were not associated with foal mortality in this study. Cortisol and thyroid hormones did not have prognostic value in the first hours of life.