title: Thyroid function and dysfunction in term and premature equine neonates.
abstract: BACKGROUND
  This study was performed to compare thyroid function of premature foals to term foals.
  
  
  OBJECTIVE
  Premature foals are more markedly hypothyroxinemic than expected for their severity of illness alone.
  
  
  METHODS
  Twenty clinically normal term foals; 28 sick, hospitalized term foals; 24 sick, hospitalized premature foals.
  
  
  METHODS
  Thyroid hormones (TH) and thyrotropin (TSH) were measured, both at rest and in response to thyrotropin-releasing hormone (TRH), in the 3 groups of foals. Clinical and clinicopathologic data were recorded.
  
  
  RESULTS
  Normal foals had high TH at birth, which decreased over the first month into the normal reference range for adult horses. TSH was within the normal adult reference range soon after birth, and did not change over time. At 24-36 hours of age, triiodothyronine (T3) was significantly lower in both premature and term hospitalized foals compared to normal foals; premature foals were not different from term hospitalized foals. Thyroxine (T4) was not different between normal and term hospitalized foals, but was significantly lower than in premature foals of both of these groups. TSH was not different among the 3 groups. TRH stimulation tests identified significant differences in T4 among all 3 groups of foals, whereas T3 was similar in premature and term hospitalized foals and different from normal foals. TSH response to TRH was significantly higher in premature foals compared to normal foals.
  
  
  CONCLUSIONS
  The hypothalamic-pituitary-thyroid axis is different in foals compared to adult horses. Sick foals exhibit nonthyroidal illness syndrome. Premature foals are more markedly hypothyroxinemic than can be accounted for by their severity of illness alone.
authors.affiliation: Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, NC.
authors.forename: B A
authors.initials: BA
authors.lastname: Breuhaus
mesh_terms: D000818:Animals; D000831:Animals, Newborn / Q000097:blood / Q000502:physiology*; D006734:Horse Diseases / Q000097:blood / Q000503:physiopathology*; D006736:Horses; D047928:Premature Birth / Q000662:veterinary*; D013959:Thyroid Diseases / Q000097:blood / Q000503:physiopathology / Q000662:veterinary; D013961:Thyroid Gland / Q000502:physiology; D013963:Thyroid Hormones / Q000097:blood* / Q000502:physiology; D013972:Thyrotropin / Q000097:blood / Q000502:physiology; D013974:Thyroxine / Q000097:blood / Q000502:physiology; D014284:Triiodothyronine / Q000097:blood / Q000502:physiology
chemical_list: D013963:Thyroid Hormones; D014284:Triiodothyronine; D013972:Thyrotropin; D013974:Thyroxine
keywords: Foal; Hypothyroidism of prematurity; Nonthyroidal illness syndrome; Thyroid hormone