Description    Myriad problems have been attributed to low thyroid function but hypothyroidism is poorly defined in horses. Excessive iodine intake can cause congenital or acquired goiter. Iodine deficiency has been associated with goiter in the newborn foal; signs vary from thyroid swelling only to systemic signs with weakness and neonatal death. Foals had a variety of congenital musculoskeletal deformities in conjunction with hyperplastic goiter of unknown cause. The thyroid glands of foals with histologic changes consistent with goiter may not be enlarged, so diagnosis requires histology of the gland and finding associated anomalies, such as rupture of the common digital extensor tendons, forelimb contractures, immature carpal and tarsal bones, and mandibular proganthism.
Species   Equine
Signs   Abnormal forelimb curvature, Abortion or weak newborns, Alopecia, Anorexia, Contracture fore limb, leg, Dryness of skin or hair, Dyspnea, Forelimb lameness, Forelimb swelling, Generalized weakness, Head, face, ears, jaw, nose, nasal, swelling, Hindlimb lameness, Hindlimb swelling, Hypothermia, Inability to stand, Increased respiratory rate, Kyphosis, Lack of growth or weight gain, Laryngeal, tracheal, pharyngeal swelling, Laxity or luxation of a hindlimb joint, Malformation of jaw, Neck swelling, Prolonged gestation, Scoliosis, Torticollis
References   Haywood L. Gestation length and racing performance in 115 Thoroughbred foals with incomplete tarsal ossification. Equine Vet J 2018;50:29 [Web Reference]
Coleman MC. Orthopedic Conditions of the Premature and Dysmature Foal. Vet Clin North Am Equine Pract 2017;33:289 [Web Reference]
Durham AE. Therapeutics for Equine Endocrine Disorders. Vet Clin North Am Equine Pract 2017;33:127 [Web Reference]
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