Pre-lamb treatment of ewes with iodine
In New Zealand, most occurrences of goitre seem to be associated with goitrogens in the feed which block the uptake of inorganic iodide by the thyroid gland. Plants of the Brassica species i.e. kales (also low in iodine), cabbages, Brussel sprouts, and broccoli may contain high levels of goitrogens. Certain NZ cultivars of clover also contain high levels of goitrogens.
Iodine deficiency tends to occur in high rainfall areas such as the Manawatu. Within each type of feed, considerable variation occurs from year to year which is reflected in the incidence and severity of goitre in newborn lambs born to ewes grazing such feed.
Interestingly, the ingestion of soil in years of drought or high stocking rates is said to reduce the incidence of goitre.
A characteristic sign of iodine deficiency is an enlarged thyroid gland in the newborn lamb (goitre), while subclinical iodine deficiency in the ewe leads to a decreased twinning rate, an increased neonatal mortality, low birth weights and poorer wool production.
It is recommended to drench ewes with potassium iodide 8 and 4 weeks pre-lambing for the prevention of iodine deficiency. However, experience in the field suggests that if you are wishing to dose the ewes once only, then treating around mid-pregnancy (i.e. at scanning) is best rather than closer to lambing.
This is because severe iodine deficiency in ewes causes reduction in foetal brain development and body weight from as early as 70 days gestation (i.e. mid-pregnancy) to lambing.
Another option, particularly if feeding a winter Brassica crop is Flexidine. Flexidine is an oily injection containing organically bound iodine providing a long-term depot of iodine. It is recommended to treat ewes 1 month before mating (at least 2 months prior to feeding crop), or not less than 2 months before lambing.
If you would like advice or information on treating your ewes pre-lamb with iodine, please contact the Feilding branch of Totally Vets.
