Although spring calving is as good as wrapped up on a lot of farms, farmers are being advised to watch out for goitre before turning late calvers out to grass.

Goitre, which is an enlargement of the thyroid gland in unborn calves and typically related to iodine deficiencies, was listed in the top 10 abortion diagnoses recorded by the Animal and Plant Health Agency (APHA) between April and June last year.

Therefore, farmers are being urged to check trace element balances in dry cows before turning them out to grass.

Cows that slipped through the cracks in the breeding season last year, but were got by the bull at a later date will be at the highest risk, as the calves’ demand for trace elements coincides with the cow moving out to pasture.

More than likely, the herd will have had dry cow minerals supplemented into their diet while housed, but the feeding of these minerals may be overlooked if the dry cows do get out, which further ups the risk factor.

Iodine deficiency

Veterinary surgeon at Shepton Vets in Somerset, England, Paddy Gordon explained that iodine deficiency is most often seen in grazed cattle late in gestation.

“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, Gordon advises farmers calving from May onwards should also be aware of the risk if dry cows are being grazed earlier in the year.

He added that the risk will depend on individual farms, grazing and forage quality.

“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,” Gordon said.

He advises that dry cows can be blood tested to check for trace element deficiencies.

In cases where stillbirth or abortions happen, post-mortem examinations may also help determine the cause, an enlarged thyroid gland being the obvious sign of iodine deficiency.

Gordon stressed 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.”

Selenium levels are also important, such 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.

Gordon highlighted research from Ireland involving 44 dairy farms which found that pasture-only diets provided only around 50% of iodine requirements.

This study also reported that 87% of forage samples contained less than 0.5mg iodine per kg of dry matter.

This supporting the case for iodine supplementation in dry cows grazing grass alone.

He said: “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.”