Iodine (i) is one of the seven essential trace elements for grazing animals.
It is unique among minerals because a deficiency can lead to a specific, and easily recognisable, thyroid gland enlargement.
The other six trace elements are cobalt, copper, iron, manganese, selenium and zinc.
Symptoms
Iodine is important in the synthesis of the thyroid hormones, thyroxine and triiodothyronine, which regulate energy metabolism in animals.
i deficiency is usually first detected in calves within a herd. Calves can be born with a goiter (enlarged thyroid gland), but deficiency may also present itself as hairless, weak or dead calves.
Symptoms in older cattle include irregular oestrous cycle, poor conception rates, abortions and retained placenta.
Iodine supplementation
In Ireland, grazed grass is the cheapest feed and is used to fuel our national dairy herd, but in most cases it provides inadequate i to meet lactating cow requirements.
Because of this, i supplementation is required. The recommended rate is 12mg/day, unless iodine deficiency has been diagnosed on your farm.
If this is the case, consultation with your vet and/or nutritionist is advised.
Research
Teagasc research found that, on average, a pasture-only diet provided 0.25mg i/kg/DM. So for a cow eating 17kg DM, this means an intake of 4.25mg i/day on grass only.
Additional i should be offered so that the cow receives the recommended supplementation of 12mg/day.
This means if 2kg concentrate is offered to cows, it should be formulated to the 12mg/day i total feeding rate.
If higher feeding rates or alternative sources of i are used on farm, the inclusion rate in the concentrates fed should be reduced accordingly.
It is also important to note that i can easily be leached during wet weather in winter and spring. Cattle requirements for i increases during unsettled, cold weather.