Friday, March 29, 2024

Iodine deficiency perplexes

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Iodine is important to ewe fertility and lamb survivability but a recent North Island onfarm study shows large gaps in our understanding. The 2012 study was held on Taratahi Agricultural Training Centre’s Mangarata Farm, currently a FarmIQ focus farm. The 518ha hill-country Wairarapa property is geographically within an area where there has been evidence of iodine deficiency. Many parts of the country have been identified as being deficient in iodine, including the pumice soils in the North Island as well as localised areas of Waipukurau, Napier and Gisborne. Large pockets of the South Island are also considered deficient.
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Mangarata already had a policy to supplement ewes with iodine but as part of the study, 430 two-tooth ewes received iodine supplementation in February 2012 and a control group of 280 two-tooths did not. At the time of supplementation blood serum iodine levels were 20ug/l and by scanning, untreated ewes levels were 22ug/l but treated ewes had risen to 29ug/l.

In 2013, as a result of making significant inroads into iodine testing techniques, Gribbles Veterinary diagnostic laboratory reduced the reference margins of iodine deficiency for both sheep and cattle to serum iodine concentrations of 45+ ug/l (adequate), 20-45ug/l (marginal) and less than 20ug/l (deficient).

Scanning results on the farm were similar for both mobs – 185% treated versus 188% untreated – with the small variance considered statistically insignificant. Docking results were also not statistically significant – treated 152% versus untreated 155% – although there was evidence suggesting untreated ewes gave birth to lambs with slightly enlarged thyroids.

Masterton veterinarian Stuart Bruere said the outcome might, on the face of it, appear disappointing but he said it merely reflects how challenging the area of iodine is and highlights the need for more research.

He said uptake of iodine by stock can vary between years and this is why in a very dry or drought-ridden year animal iodine levels can be higher as more soil, which contains iodine, is ingested.

In a season of good growth, where animals might graze abundant pasture, less soil is ingested but iodine levels can be further decreased if the pasture is heavy in white clover as it contains goitrogens, albeit in lower levels than brassicas. Goitrogens reduce the uptake of iodine by the thyroid gland, hindering production of thyroid hormones.

Dr Bruere said much of the current thinking about iodine supplementation is taken from one-off research projects when it would benefit the industry greatly to replicate these, but there doesn’t seem to be a lot of enthusiasm to do this.

He is aware of more farmers reporting little to no difference in scanning rates after supplementing with iodine, but increased survivability in lambs born, and he considers much value can be gleaned by research to give farmers a better understanding as to why this is occurring, including more research into dose rates and timing of doses.

It is also important to get a better understanding why, in one year, animals can be deficient but not the next. It is essential to test over multiple years to build a more accurate picture of iodine status. If farmers just rely on one year’s results, they could be easily misled and potentially lose production or incur unnecessary expense.

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