IODINE IN THE HORSE - SOURCE, Inc.

IODINE IN THE HORSE
TOO MUCH OR TOO LITTLE - page 2 of 2

... England four foals were born with greatly enlarged thyroids and leg weakness. One mare also had an enlarged thyroid. Feed analysis showed that the mares had received 83 mg I/day from a proprietary feed during pregnancy. The year before the introduction of this proprietary feed, the mares received a vitamin / mineral supplement which supplied about 12 mg I/day and there was no problem with goiter on the farm. The results of these studies are summarized in Figure 1. It appears from these reports, that around 50 mg of dietary iodine is required in the daily rations of mares to produce any incidence of goiters in their foals. One other study (Driscoll et al, 1978) reported goitrous foals from mares receiving 35 mg I/day. There is some question, however, about what levels of iodine the mares in this study actually received. The authors reported that the mares were given 12 ounces per day of a supplement which was reported to contain 58 PPM iodine. The guaranteed analysis on the product's label stated that it contained 340 PPM iodine and independent analyses of the same product revealed that it contained at least 580 PPM iodine, a level 10 fold higher than reported in the paper. Using the manufacturer's guarantee, the mares would have received a total of 131 mg I/day and according to the independent analyses, a total of 212 mg I/day. These levels are within the ranges reported to produce goitrous foals in other studies.

Dietary Iodine
Toxic dietary iodine concentrations may result from adding excessive supplemental iodine, such as from ethylenediamindihydroiodide (EDDI), to concentrates or from using feedstuffs high in iodine. A common feedstuff that may contain excess iodine is kelp (Laminariales), a specific family of seaweeds that may contain as much as 1,850 PPM iodine (NRC,1989). Unfortunately, people have a tendency to classify all seaweeds as kelp just as the layman might consider every breed of horse a Thoroughbred. There are numerous other specific seaweeds that contain considerably less iodine than kelp. SOURCEŽ, a dietary micronutrient supplement for horses, CONTAINS NO KELP. It is made from a blend of certain other dehydrated seaweeds including Fucaceae, Palmariaceae, Gigartinaceae, Bangiaceae, and
Ulvaceae. The seaweeds of these Families which are utilized in SOURCE contain considerably less iodine than kelp. In addition, all components used in SOURCE are analyzed for iodine, as is the final product blend. SOURCE, at the recommended feeding level of 1/2 ounce per 1,000 lbs. body weight, provides approximately 9 mg of iodine. This amount of iodine is well below the levels reported to cause problems in horses. In fact, many of the "control" farms reported in the literature fed this level of iodine to their horses with no suggestion of iodine toxicity in either the mares or foals.

Conclusions
Goiters in horses can be cause by either too much or too little dietary iodine. It is of paramount importance that the actual dietary intake of iodine and the possible presence of goitrogenic substances be established before treatment is administered. All too often, additional iodine is given to goitrous horses when the diet already contains excessive iodine. The mare's ration should be evaluated in instances of foal goiter since iodine can be concentrated in the fetus and in milk. A common culprit in many cases of iodine toxicity in horses is kelp. SOURCE contains no kelp and at its recommended level of intake provides a safe and effective amount of dietary iodine which will safeguard against iodine deficiencies in horses.

References

Baker, H.J. and J.R. Lindsey. 1968. Equine goiter due to excess dietary iodine. J. Am. Vet. Med. Assoc. 153:1618.

Drew, B., W.P. Barber, and D.G. Williams. 1975. The effect of excess iodine on pregnant mares and foals. Vet Rec. 97:93

Driscoll, J. et al. 1978. Goiter in foals caused by excess iodine. J. Am. Vet., Med. Assoc. 173:858

Kruzkova, E. 1968. Mikroelementy i vos proizvoditel-'naja funkeija kobyl. Tr. Vses. Inst. Konevod-stvo. 2:28 (as cited in Nutr. Abst. Rev. 39:807, 1968).

National Research Council. 1989. Nutrient Require-ments of Horses. Washington D.C.: National Academy Press.

National Research Council. 1980. Mineral Tolerance of Domestic Animals. Washington D.C.: National Academy Press.

Sipple, W.L. 1969. A Veterinarian's Approach to Stud Farm Nutrition. Eq. Vet. J. 1:203

"IODINE IN THE HORSE
TOO MUCH OR TOO LITTLE"

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