Serum cortisol and thyroid hormone concentrations and survival in foals born from mares with experimentally induced ascending placentitis.

Abstract

BACKGROUND: There are few publications on occurrence of nonthyroidal illness syndrome in foals and on the prognostic value of cortisol and thyroid hormone (TH) concentrations in newborn foals. OBJECTIVES: To determine serum cortisol and TH concentrations (total and free thyroxine: TandT; total and free triiodothyronine: TandT) in foals born from mares with placentitis, to determine their association with survival, and their use as prognostic markers. ANIMALS: A cohort of 29 newborn foals comprising 5 Control, 14 Low-risk, and 10 Sick foals were evaluated over the first week of life. METHODS: In this prospective study foals born to mares with experimentally-induced placentitis were assigned to Low-risk or Sick groups while foals born to control mares were classified as Control based on clinical findings. Foals were also classified as Term (n&#x2009;=&#x2009;13), Dysmature (n&#x2009;=&#x2009;7), or Premature (n&#x2009;=&#x2009;9), and survival rate was recorded. Serum cortisol and TH hormone concentrations were measured at 0, 12, 24, 48, and 168 hours of life. RESULTS: Sick non-surviving foals had lower (P&#x2009;<&#x2009;.05) T: cortisol ratio at 12 (3.68&#x2009;&#xb1;&#x2009;1.06 versus 18.58&#x2009;&#xb1;&#x2009;2.78), 24 (5.47&#x2009;&#xb1;&#x2009;2.34 versus 23.40&#x2009;&#xb1;&#x2009;3.82), and 48 (10.47&#x2009;&#xb1;&#x2009;6.29 versus 26.6&#x2009;&#xb1;&#x2009;2.90) hours of life when compared to Sick surviving foals and lower (P&#x2009;<&#x2009;.05) T: cortisol ratio at 12 (75.12&#x2009;&#xb1;&#x2009;21.71 versus 414.47&#x2009;&#xb1;&#x2009;58.47) and 24 hours (127.83&#x2009;&#xb1;&#x2009;55.21 versus 430.87&#x2009;&#xb1;&#x2009;80.31) after birth than Sick surviving foals. CONCLUSION AND CLINICAL IMPORTANCE: Placental infections can impair fetal thyroid function. Low T: cortisol and T: cortisol ratios seem to be good prognostic markers in newborn foals.