Iodine Supplements for Livestock

Phil Rogers MRCVS <philrogers@eircom.net>
Grange Research Centre, Dunsany, Co. Meath, Ireland
21-Aug-2001

IODINE (I) DEFICIENCY IN IRISH CATTLE AND SHEEP

I-deficiency is endemic in cattle and sheep in Ireland. The prevalence of low I-status in unsupplemented animals at pasture is >80%. The body recycles I poorly. In supplemented animals in I-deficient groups, PII falls within 5-15 days of removal of I-supplement.

Confirmation of low I status: A blood test for plasma inorganic I (PII) is the most reliable way to confirm a low I-status in a problem group. Ideally one should test 10 animals individually. Low to very low I-status is confirmed if the group mean PII is <50 ug/L, or >50% of the group are <45 ug/L. Plasma T₃ and/or T₄ tests are unreliable in assessing I status. Bulk milk I tests are unreliable unless they are low - "normal" milk I values may arise in I-deficient herds if iodine-based disinfectants contaminate the bulk tank.

Clinical and subclinical signs of I-deficiency have been confirmed in herds and flocks throughout the state. In cattle, the signs include various combinations of low fertility (inactive ovaries, delayed puberty, anoestrus, repeat breeding, embryo loss); low calf survival (abortion, stillbirth/weak calves, small calves, goitre); high incidence of calving problems (placental retention, lazy/prolonged calving); low immunity to infection (scour, pneumonia, joint-ill, mastitis, metritis etc); low milk yield and growth rate; disturbances of general metabolism. Similar problems occur in sheep.

Non-clinical I-deficiency is common: Most low I-status animals are clinically healthy; they show no signs of I-deficiency, or apparent depression of health or productivity. I-supplementation of such animals usually does not improve their health, productivity or profitability.

Daily target for I-supplementation: The target suggested for I-supplementation is 10 mg I/100 kg LW/d, or about 60 mg I/d for cows, 6 mg I/d for ewes. Pro rata supplements are suggested for other ruminants. As long as the animals get this level of I-supplement during the critical times of the year, it does not matter whether the supplement is given in the feed, on the feed, or via the water supply.

Breeding animals: Critical times for I supplementation are late pregnancy (especially in the last month), at peak lactation and before/during the breeding season, until pregnancy is confirmed by veterinary examination (rectal or ultrasound). In herds with non-infectious abortions, I-supplement may be needed throughout pregnancy

Young and growing animals: Signs of I-deficiency include low immunity to infection, low growth rate, poor coats. Similar signs may be due to other factors (inadequate quality/ quantity of feed, parasitism, chronic infections, other mineral deficiencies etc. Differential diagnosis is important. Young and growing animals may need I-supplements if they show signs of I-deficiency and if blood tests show low PII.

A. IODISED FEEDS OR MINERAL MIXTURES

Assuming that cows need a supplement of 60 mg I/d, one must assess their supplements on two criteria: (a) the level of supplementary feeding (kg/cow/d) and (b) the level of I in the supplement (mg/kg). In all cases, (a) X (b) must = 60. For example, iodised concentrates, to be fed at 8 to 0.5 kg/cow/d, or mineral mixtures to be fed at 150, 125 or 100 g/cow/d (0.150, 0.125 or 0.100 kg/cow/d), must contain the following I-levels:

Assuming that ewes need a supplement of 6 mg I/d in a concentrate allowance of 2 to 0.25 kg/ewe/d, or in iodised mineral mixes fed at 30 to 15 g/ewe/d (0.030 to 0.015 kg/ewe/d), a similar table for ewes is:

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B. 4% KI-MIXTURE AS A SIMPLE I-SUPPLEMENT

If animals need an I-supplement (and other I-supplements are not being provided), trough water can be medicated by 4% potassium iodide (KI) mixture cheaply and effectively. Vets or pharmacists can make a 4% KI-mixture in bulk for use as an I-supplement in I-deficient animals:

SHAKE the mixture until the KI is fully dissolved

For supplies of KI try: Foran Chemicals (Tallaght, Dublin); Galavans Feed Supplements (Clonroche); Griffin's Pharmacy (Tullow, Co. Carlow); Kennedy's Pharmacy (Hacketstown, Co. Carlow); NutriBio Ltd (Cork City); Taylor's Feeds (Collinstown, Co. Westmeath).

LABEL THE 4% KI-MIXTURE CLEARLY, AS FOLLOWS:

• KI-MIXTURE: Contains 40 mg KI (= 30 mg I)/ml. POISON. For animal treatment only. Keep away from children. For use as an I-supplement for animals. Use ONLY in ANIMALS and ONLY as DIRECTED.
• USAGE OF KI-MIXTURE: I-deficient animals need I-supplements at frequent and regular intervals during the times of greatest risk.
• DOSE :

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• DO NOT EXCEED THE DOSE, EXCEPT ON VETERINARY ADVICE
• Do not use together with other high-I sources (such as high-I mineral mixes, compound feeds supplying high I etc). Alternatively, if animals are getting only part of their daily I target from other sources, reduce the KI-dose accordingly to make up the deficit. For example, if cows are getting 20 mg I/d from another source and the target dose is 60 mg I/d, top up by giving another 40 mg I (1.33 ml of 4% KI-mixture)/d.
• SHAKE CONTAINER well before removing the daily group dose. Trace-element mixtures may precipitate on storage. Failure to shake the container frequently during use may cause sedimentation. The upper layer of the mixture may contain low levels of trace-elements and the lower layer may contain toxic levels. Animals dosed from the upper layer may get too little supplement. Those dosed from the lower layer can die of acute poisoning within a few days.

METHODS OF GIVING THE 4% KI-MIXTURE

The KI-mixture can be given to animals: (a) individually, daily via water/milk/feed containers, or (b) to groups, daily via the trough water, or (c) to groups, daily via the feed (silage / hay / concentrate), or (d) individually, by drench at intervals of 2-3 weeks.

a. 4% KI-MIXTURE VIA INDIVIDUAL WATER/MILK/FEED BOWLS

If animals (horses, veal calves etc) are watered or fed individually, the KI-mixture can be added once/d to the feed or drinking container.

0. Check the daily dose for each animal, according to the stated dose rates. For example, a mare would get 1 ml/d; a veal calf (50 kg) would get 0.33 ml/d.
1. SHAKE CONTAINER well before removing the daily dose.
2. Remove the daily dose into a 1 ml syringe.
3. Add the daily dose (once/d) to the feed or drinking bowl/bucket.

b. 4% KI-MIXTURE VIA THE WATER SUPPLY

If there is a controlled trough-water supply, and the animals have no other source of drinking water (streams, ponds etc), it is most convenient to add this mixture to the trough water for prophylactic medication of I-deficient groups of animals.

Note: Young lambs and calves (especially those suckling their dams) may drink little or no water. Hence, this method of I-supplementation may not be relied upon in those animals.

0. Calculate the daily dose for the group, according to the stated dose rates. For example, 50 cows would get 50 X 2 (= 100 ml)/d; 48 store cattle would get 48 X 1 (= 48 ml)/d; 350 ewes would get 350 X 0.20 (= 70 ml)/d.
1. SHAKE CONTAINER well before removing the daily group dose.
2. Remove the daily dose for the group  into a calibrated flask or container.
3. Split the dose over the day: If the whole dose is added once/d to small troughs, the early drinkers may take too much, leaving too little for the others. Therefore, add 50% of the daily group dose twice/d ( or, preferably, 33.3% three times/d) to the trough water. On the last addition of each day, rinse the calibrated container in the trough water to ensure that no sediment remains in the calibrated container.
4. Stir the water in the trough thoroughly after each addition of KI-mixture.

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c. 4% KI-MIXTURE VIA THE FEED (SILAGE/HAY/CONCENTRATE)

If animals are fed forage (silage or hay) or concentrate, it is convenient to squirt this mixture evenly over the forage for prophylactic medication of I-deficient groups.

0. Calculate and remove the total daily dose for the group, as in (b 1, 2 and 3) above.
1. Spray 50% of the day's dose over the feed on two occasions daily, in a fine jet from syringe and fine needle, or a suitable spray-gun (such as a "Windowlele" or "Dettol" spray-dispenser).

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d. 4% KI-MIXTURE BY DRENCH AT INTERVALS OF 2-3 WEEKS

Drenching at intervals of 2-3 weeks may be the only realistic option if methods (a to c) above are impractical, for example in suckler calves, or in flocks of sheep. In that case, suggested doses for drenching are:

DOSE (ml/head) for use at intervals of 2 or 3 weeks:

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• DO NOT EXCEED THE DOSE, EXCEPT ON VETERINARY ADVICE

HORSES need less iodine (mg/kg body weight) than ruminants. In particular, avoid the use of excessive I-supplement in mares in late pregnancy, or young foals. Toxic goitre can arise if those animals ingest excessive amounts. I supplements for mares in late pregnancy should not exceed 30 mg/d. 

C. AQUADYNE TABLETS VIA TROUGH WATER

Mayo Healthcare (Westport) supplies Aquadyne "slow-release" tablets (420 mg I/tablet). To medicate the trough water for a herd of cattle, the dose (D) of tablets is calculated as follows:

1. Estimate the total liveweight of the cattle to be dosed (TLW, in kg).
2. Decide on the dosing interval (DI, in days). DI should be every 1 to 7 days, say twice/week, or at an interval of 3.5 days.
3. D = (TLW * DI/4200). Thus, a herd of Friesian cows (or other Friesian cattle), with a total estimated liveweight of about 34500 kg, would need 34500 * 1/4200 = 8.2 (say 8-9) tablets at intervals of 1 d, or 34500 * 3.5/4200 = 28.75 (say 29) tablets twice/week.

Add fresh tablets at the predetermined dose interval to the simple dispenser (supplied by the company). Immerse the dispenser in the water trough. Remove the spent tablets, as needed, from the opposite end of the dispenser.

D. IONOX BOLUSES FOR CATTLE

These are slow-release ruminal boluses, made by Animax UK, and distributed by Bayer (UK and Ireland). They contain I, Co and Se. An oral dose of 2-3 boluses/cow would provide sufficient I, Co and Se to protect herds which would otherwise be severely deficient in those minerals for a period of 5-7 months. In my opinion, the main role for slow-release bolus-technology is in beef cows, beef cattle, or young dairy-replacements at pasture, when water medication, or provision of carrier feeds high in trace-element supplements may not be a practical option.