Dr Rick Last – Specialist Veterinary Pathologist
During the winter months we experience an increase number of abortion submissions with enlarged thyroid glands and / or hypertrophic cardiomyopathy with hydropericardium, hydrothorax and ascites, lung oedema and nodular irregular livers (chronic cardiogenic congestion / cyanotic induration). Such pathology (in the absence of histological myocarditis), indicates that underlying micronutrient deficiencies / imbalances, mycotoxins and endocrine disrupting agents would need further investigated.
Enlarged thyroid glands (hyperplastic goiter) in late stage abortions, stillbirths, perinatal deaths or weak neonates in cattle, sheep and goats, should alert the investigator to possible underlying micronutrient deficiencies / imbalances (iodine, selenium, copper, manganese, iron) especially when accompanied by cardiomyopathy, ingestion of goitrogenic plants / anti-thyroid compounds by the dam, in-utero exposure to certain toxic agents (mycotoxins) or ingestion of endocrine disrupting agents by the dam. Similar pathology has also been observed in aborted fetuses of various antelope species.
Historically this condition has been linked to livestock being farmed in iodine deficient areas. Supplementation of iodine through the use of iodized salt (sea salt) in licks is used extensively in these areas to control this condition. Problems frequently arise when the sea salt source in the lick is replaced with pan salt (low iodine content). Selenium deficiency alone or in combination with iodine deficiency or other factors is now believed to be an important emerging factor in hyperplastic goitre in South Africa. Outbreaks of a heart failure syndrome in full term bovine fetuses associated with hyperplastic goiter, hypertrophic cardiomyopathy and chronic hepatic congestion (cyanotic induration), have been linked to low selenium levels in fetal liver tissue.
Goitrogenic compounds as found in Brassica spp and certain pharmacological agents (sulphonamides, thiouracil), can also induce congenital hyperplastic goiter in fetuses when dams are exposed. Iodine deficiency can also be induced by ingestion of anti-thyroid compounds present in animal feeds and particularly important in this regard is prolonged low level exposure to the cyanates / prussic acid containing plants (Trifolium spp, Cynodon spp, Linseed meal etc), which function via inhibiting iodine trapping.