Nia Williams, Technical Manager at Nettex
Farmers Urged To Check Iodine Status As Goitre Linked To Late Abortions
1 week ago 
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Farmers turning cows out to grass are being urged to check trace element balance in dry cows, after goitre was listed among the top 10 abortion diagnoses recorded by the Animal and Plant Health Agency (APHA) between April and June last year (2025)1.
Paddy Gordon, veterinary surgeon at Shepton Vets, says farmers should be aware of iodine deficiency when turning dry cows out to grass, as it can cause goitre, an enlargement of the thyroid gland in unborn calves.
“Iodine deficiency is most often seen in grazed cattle in late gestation,” he explains. “If grass is deficient and as foetal demand for trace elements increases in late pregnancy, there can be a risk of deficiency, which may lead to late abortions, stillbirths or weak calves.”
While iodine deficiency is often associated with late summer when dry cows are out grazing, Mr Gordon says farmers calving from May onwards should also be aware of the risk if dry cows are being grazed earlier in the year.
“The risk will depend very much on individual farms, grazing and forage quality,” he adds. “Iodine is a vital trace element for metabolism, being essential for the production of the thyroid hormones, so it’s important to consider it and plan accordingly.”
Mr Gordon advises that dry cows can be blood tested to check for trace element deficiencies. In cases where stillbirths or abortions occur, post-mortem examinations may also help determine the cause, with an enlarged thyroid gland the obvious sign of iodine deficiency.
He stresses that trace element monitoring should form part of a herd’s overall health plan
“Trace element status and assessment should form part of the herd health plan with a vet,” he says.
Selenium levels are also important, as a deficiency can contribute to iodine and thyroid issues. Selenium plays a key role in activating thyroid hormones and is also essential for immune function in both cows and unborn calves.
Mr Gordon highlighted research from Ireland involving 44 dairy farms which found that pasture-only diets provided only around 50% of iodine requirements. The study also reported that 87% of forage samples contained less than 0.5 mg iodine per kg of dry matter, supporting the case for iodine supplementation in dry cows grazing grass alone2.
“The broad message is to know the issues on your farm,” he says. “Test your forage, look out for challenges, and consider whether trace elements could be contributing. Work with your vet to develop a plan, because every season is different.”
Practical supplementation
When iodine deficiency is considered a risk, farmers can use boluses to help ensure the cow and unborn calf receive adequate supplementation.
According to Nia Williams, Technical Manager at Nettex, boluses can be particularly useful when animals at risk of deficiency are turned out to graze or managed away from the farm.
“In cases where animals are known to be low in iodine, administering a high-iodine bolus, such as EnduraBol High Iodine at drying off, can provide a slow, controlled release of iodine throughout the dry period, lasting up to 180 days.
“This approach ensures every cow receives the correct level of supplementation,” she explains.
Iodine supplementation during the dry period supports foetal development and can help prevent issues such as weak calves and the risk of goitre. Maintaining adequate iodine levels can also help to support subsequent fertility and immune system function in cows.
Ms Williams advises farmers consult their vet or nutritionist before introducing supplementation and confirm the herd’s trace element status.
“Using an iodine bolus for dry cows is a proactive management tool,” she says. “It helps prevent iodine deficiency during critical non-lactating periods and supports the health of both the cow and the developing calf.”
References:
- Great Britain cattle quarterly report, disease, surveillance and emerging threats. Volume 29: Quarter 2 (April to June) 2025.
https://assets.publishing.service.gov.uk/media/692085b925317fc65a5cfdc9/2025_Q2Cattle_Emerging_Threats_Report.pdf - Nutrition in cattle – essential trace elements. Vet Times. 25th Aug 2022.
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