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Part 5. Biochemical function of deficient minerals in Harrison County, Indiana hay/pasture.
We now have a balanced mineral diet and know what minerals must be supplemented. A fair question to ask at this point is “How important are these supplements to horse health?” There is an extensive amount of literature on the role of minerals in equine diets. You can refer to several of the links provided above for more details, or link to Dr. Eleanor Kellon's blog. Rather than present a comprehensive literature review, we have attempted to summarize this information in Table 1. Table 1 is not all-inclusive but illustrates some of the primary functions of minerals deficient in Harrison County, Indiana hay and pasture, and symptoms associated with deficiencies. Manganese (Mn) has been omitted because of the limited nature of our database on pasture grass. None of the hays tested were Mn-deficient.
Part 6. Iodine deficiency and supplement analysis
Table 1 includes one additional mineral in our list of deficient minerals in Harrison County, Indiana hay and pasture. The mineral iodine, which is critical to thyroid function, is not included in the nutrient profile provided by forage labs because the analysis is difficult and expensive. However, most soils are deficient in iodine, which is the reason why iodized salt is recommended in human diets. Iodine levels can be determined indirectly with a full thyroid panel, which includes blood T4 (levothyroxine) and T3 (triiodothyronine) hormone levels.
Table 1 includes one additional mineral in our list of deficient minerals in Harrison County, Indiana hay and pasture. The mineral iodine, which is critical to thyroid function, is not included in the nutrient profile provided by forage labs because the analysis is difficult and expensive. However, most soils are deficient in iodine, which is the reason why iodized salt is recommended in human diets. Iodine levels can be determined indirectly with a full thyroid panel, which includes blood T4 (levothyroxine) and T3 (triiodothyronine) hormone levels.
The major contribution to iodine in soils is from the volatilization of iodine from the ocean surface, e.g., vapor emissions from algae (Iodine and Inorganic Iodides: Human Health Aspects, Risher, JF and Keith, S, ed., World Health Organization, 2009). In general, there is a good correlation between iodine concentration versus distance from the ocean. Because soils form by weathering (physical and chemical decomposition) of underlying rocks, the chemical composition of parent rock can also affect the concentration of iodine in soils. For example, soils formed from igneous and metamorphic rocks (e.g., granite, volcanic rock and gneiss) are generally lower in iodine than those formed from sedimentary rocks (e.g., limestones and sandstones). This accounts for the lower iodine concentrations in the Upper Midwest and Great Lakes region (“Goiter Belt”), and the Northeast and Northwest U.S. (Fig. 1).
Fig. 1. Iodine deficient soils (hachured) in the U.S. The Upper Midwest and Great Lakes region form what is known as "The Goiter Belt". Source: Salt Institute
Possible iodine supplements include iodized (with potassium iodide spray) table salt (e.g., grocery store salt), calcium iodate, organic iodine (as opposed to inorganic forms, such as potassium iodide) in the form of ethylenediamine hydroiodide (EDDI), ocean kelp and naturally occurring ancient sea salts, such as Redmond salt.
Let’s take a closer look at each of these supplements.
Iodized Salt
1. The average iodine content for all U.S. brands of iodized salt is 47.5 mg/kg +/- 18.5 mg/kg, i.e., iodine content ranges between 66 and 29 mg/kg, or 66 and 29 ppm. The ppm values correspond to 1.84 mg/ounce salt (66 mg/kg x 0.028 kg = 1.84 mg/ounce) and 0.81 mg/ounce salt (29 mg/kg x 0.028 kg = 0.81 mg/ounce) (Dasgupta et al. 2008).
2. About 2.5-3 ounces of iodized salt at the average concentration (47.5 mg/kg x 0.028 kg = 1.3 mg/ounce) would be needed to satisfy the minimum NRC requirement for iodine in our grass hay example (3.5 mg per day, Nutrient Requirements of Horses, 2007). The minimum NRC requirement for sodium at average maintenance is 10 grams (Table 2, Part 2), or 26 grams (about 1 ounce), supplemented as sodium chloride (remember that sodium chloride consists of 39% sodium and 61% chloride). In other words, using iodized salt for our sodium supplement will not satisfy the iodine requirement.
3. Commercial mineral/vitamin supplements formulated for this part of the U.S. contain about 1.5 mg iodine per ounce, e.g., VMAX, McCauley's Bros., Versailles, Kentucky). Horse feeds, such as Tribute Kalm ‘N EZ®, provide about 2-4 mg iodine per day for the average idle horse, depending on amount fed.
4. Iodized salt is highly refined and contains small amounts of dextrose (sugar) as a stabilizer to prevent iodine loss. If iodized salt is exposed to moist air during storage (no light), iodide in the form of potassium iodide is converted (oxidized) to iodine, which is subsequently lost to sublimation (direct transition from solid to gaseous state, e.g., snow to water vapor). Based on the study by Dasgupta et al. (2008), iodized salt will loose about 50%-60% of iodine content after 10 days for relative humidity (RH) levels between about 80% and 43 +/- 5% (ambient laboratory RH).
5. Because of its chemical instability, potassium iodide is not commonly used in animal feed. A good inorganic alternative is calcium iodate, which is very stable and contains about the same iodine percent as potassium iodide (64% versus 68% iodine).
Organic iodine (EDDI) (VEDCO)
1. Common iodine supplement for livestock. Contains a minimum of 3.65% iodine, or 37 g/kg = 37,000 mg/kg = 37,000 ppm. No maximum concentration given. Sold in 1 lb bags.
2. About 3 ounces EDDI mixed in 50 lb bag of loose white salt, or Redmond salt, provides ~4 mg iodine per ounce based on minimum concentration (3.65%), satisfying both the minimum sodium and iodine requirements.
3. Requires mixing at feed mill (400 lbs minimum at local mills), or nutrition company (smaller custom batches), to achieve homogeneous composition.
Ocean-K (dried kelp) (Uckele Health and Nutrition)
1. Minimum and maximum iodine levels are 0.05% and 0.08% (guaranteed analysis). Recommended feeding directions 0.5 to 2 scoops (1 scoop = 10 grams kelp).
2. Iodine in the form of dried kelp with other ingredients, such as sea salt (4.5% maximum), calcium, phosphorous, and potassium.
3. At maximum iodine concentration (0.08%), 1 scoop kelp (10 grams) provides
0.08% = 0.8 g /kg = 0.8 g/kg x 0.010 kg = 0.008 g = 8 mg.
At minimum concentration (0.05%),
0.05% = 0.5 g/kg = 0.5 g/kg x 0.010 kg = 0.005 g = 5 mg.
4. If you are concerned about supplementing iodine at levels slightly above the minimum NRC requirement (3.5 mg per day), supplement with smaller amounts assuming maximum concentration.
For example,
At maximum iodine concentration for 0.5 scoop (5 grams),
0.08% = 0.8 g/kg = 0.8 g/kg x 0.005 kg = 0.004 g = 4 mg.
This scoop amount will also provide 4.5% salt (sodium chloride, maximum), equivalent to 45 g/kg x 0.005 kg = 0.225 g NaCl (21 g NaCl required to meet minimum NRC requirement in our hay forage example in Table 2, Part 3).
Dried Kelp (HorseTech)
1. Minimum iodine concentration is 300 ppm (300 mg/kg = 0.3 mg/gram). Guaranteed analysis. No maximum concentration given.
2. Iodine in the form of dried kelp with potassium and sodium chloride.
3. 1 scoop holds ~5 grams dried kelp containing 1.5 mg iodine (0.3 mg/g x 5 g = 1.5 mg) at the minimum concentration. About 2.5 scoops required to satisfy minimum NRC requirement.
Redmond salt
1. Minimum and average iodine concentrations are 10 and 12 ppm, respectively. No maximum concentration given (refer to trace element analysis of Redmond salt in Part 3).
2. Supplementing with 1 ounce (28 grams) per day at the average concentration, 12 ppm iodine = 12 mg/kg x 0.028 kg = 0.34 mg, an order of magnitude (10x) less than the minimum NRC requirement for iodine (3.5 mg per day).
Take-home message
1. Minerals deficient in Harrison County, Indiana hay and pasture are extremely important to horse health.
2. Iodine is deficient in most soils and must be supplemented.
3. Iodine concentrations in hay are not determined by forage labs because the analytical methods required are difficult and expensive.
4. Iodine levels can be determined indirectly with a blood test (full thyroid panel).
4. Three possible iodine supplements are iodized salt, ethylenediamine hydroiodide (EDDI), and ocean kelp. Each of these supplements has advantages and disadvantages in terms of chemical stability, amount required, specific information on maximum iodine content and preparation.
5. Redmond salt does not provide the NRC minimum iodine requirement for adult horses at maintenance level.
1. Minerals deficient in Harrison County, Indiana hay and pasture are extremely important to horse health.
2. Iodine is deficient in most soils and must be supplemented.
3. Iodine concentrations in hay are not determined by forage labs because the analytical methods required are difficult and expensive.
4. Iodine levels can be determined indirectly with a blood test (full thyroid panel).
4. Three possible iodine supplements are iodized salt, ethylenediamine hydroiodide (EDDI), and ocean kelp. Each of these supplements has advantages and disadvantages in terms of chemical stability, amount required, specific information on maximum iodine content and preparation.
5. Redmond salt does not provide the NRC minimum iodine requirement for adult horses at maintenance level.
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