Beware iodine over-supply to pregnant ewes or cows

Livestock farmers are being advised that it’s possible to over-supplement pregnant ewes and cows with iodine, risking poor absorption of colostrum antibodies and ill health or death in new born lambs and calves.

An investigation reported by The Vet Record journal of 100 ewes, from which 40 live lambs died within a few days of birth, concluded that “probably some ewes ingested sufficient iodine to cause a reduction in colostrum absorption by their lambs” [ref 1]. The ewes were being fed daily with mineralised compound feed, and had access to mineral licks too.

In readiness for main crop lambing and onset of the spring calving peak, this alert comes from vet Dr Elizabeth Berry of Animax. “Once the daily supply of iodine is in the target zone, more is certainly not better,” she explains.

This alert to farmers is prompted by another supplier’s advertising claim of “50% more iodine than competing boluses” [ref 2]. If this is a comparison with her company’s Tracesure range, in which iodine (along with selenium and cobalt) is formulated to supply daily requirements, she says farmers using a ‘50% more’ product risk unintended over-supplementation.

In the same Vet Record report, another investigation of multiple lamb deaths at two to three days old found that hygiene and colostrum quality were good. Lamb post mortems identified normal milk clotting in the abomasum (stomach), but low levels of immunoglobulins in blood plasma, indicating “failure of maternal colostral antibody transfer.” The report suggested this was due to high levels of iodine supplementation in the ewes’ feed.

Maximum iodine levels to aim for are 9.9mg/kg of dry matter feed intake for ewes, and 4.4mg/kg DM for cows. For guidance on hitting these targets, farmers should contact their own vet or a livestock specialist at Animax.

Leaching bolus technology was developed and patented by Animax for slow release of trace elements at a regulated rate.

Animax offer a range of bolus products (copper optional) visit Animax Products or contact your local representative.

1. Veterinary Record, 9 July 2016, p42.
2. Available on request from author.

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