With around 42% of outwintered heifers being grazed on kale, producers are being alerted to the potential risk of iodine deficiency.
“Outwintering cattle on brassica crops is becoming an increasingly popular option, particularly for replacement dairy heifers, offering a good way to reduce costs over the winter period,” says Tom Butler, technical manager at the Denis Brinicombe Group.
“However, additional supplementation with minerals is crucial to maintain key targets for growth, performance and fertility, especially when grazing on kale. This is due to it containing a high level of goitrogens, which negatively impact the bioavailability of iodine and can subsequently induce a host of problems.”
Mr Butler explains that goitrogens found in kale work antagonistically with iodine, influencing the metabolism of the mineral in the animal.
“Kale contains a type of goitrogen, thiocyanate, which originates in glucosinolates found in plant matter. This interferes with the uptake of iodine into the thyroid when consumed.”
The problem can be further compounded in areas with acidic soils. “Soil pH, which varies regionally, can also affect the uptake of iodine into the plant tissue itself. This, combined with a high level of goitrogens, significantly reduces the availability of iodine in kale-based diets.
“If cattle become deficient in iodine, their health, growth and performance can be compromised, and lethargy and poor eating habits may be noticed,” says Mr Butler.
Hormone production can also be affected with an iodine deficiency impacting thyroid function.
“Fertility can be significantly affected by reduced iodine availability during the winter because a hormone imbalance can cause stillbirths and pre-natal mortality.”
Mr Butler says bolusing outwintered heifers is a good way to supplement minerals as it can provide a sustained supply of micronutrients for six to eight months.
“Administering a bolus high in iodine, such as EnduraBol, will provide an accurate and consistent release of micronutrients and help avoid any issues related to an iodine deficiency when outwintering cattle on kale or other brassicas,” concludes Mr Butler.