• Iodine plays a key role in dairy cattle energy metabolism and immunity.
• Iodine"s ability to enhance immunity has been shown to be effective in controlling foot rot.
• Goitrogenic compounds found in some common feedstuffs – such as canola, raw soybeans, turnips and nitrates – reduce iodine uptake.
• Milk with iodine levels exceeding 500 ppb is considered adulterated and is unsalable.
When thinking about the trace minerals needed in a dairy herd"s diet, the focus is often on zinc, manganese, copper, cobalt or selenium. Meanwhile, an important mineral – iodine – goes relatively overlooked. Iodine plays a key role in dairy cattle energy metabolism and immunity, impacting overall performance. It"s also important to recognize that iodine has potential to be either under or over fortified in diets.
Functions of iodine
We know iodine is necessary in human diets – so necessary that iodized table salt is found on kitchen tables everywhere. In cows, iodine is necessary for the production of thyroid-produced hormones essential for metabolic rate regulation, as well as cell differentiation, growth and development in growing animals.
Iodine also plays a role in various immune system functions, including movement of immune cells to the site of injury or attack, consumption of bacteria by immune cells and bacteria killing ability. Historically, iodine has been effective in controlling foot rot in feedlot cattle, and it may also have a role in controlling digital dermatitis in both dairy and beef cattle. Foot rot and digital dermatitis are two common infectious claw lesions.
Common signs of subclinical iodine deficiency in breeding females include suppressed estrus, reproductive failure, abortion, stillbirth, increased incidence of retained placenta and longer gestation periods.
Requirements and legal limits
The NRC (2001) guideline is an iodine dietary concentration of 0.5 ppm [dry matter (DM) basis], or about 12 mg/ head/day for a 1,500-lb. cow, milking 77 lbs./day and eating approximately 52 lbs. DM/day.
This guideline was established to achieve normal animal performance levels when consuming diets low in antagonists and under minimal stress.
In addition, goitrogenic compounds found in some common feedstuffs – such as canola, raw soybeans, turnips and nitrates – reduce iodine uptake.
Thus, the amount of iodine recommended by the NRC (2001) may be insufficient to achieve optimal enzyme functions and animal growth, immunity and performance. Depending on dairy herd stressors and rations, supplementing dairy cattle diets with 0.7 to 1.1 ppm (DM basis) iodine, depending on lactation stage, is frequently recommended.
Milk iodine levels
It is important to note that the National Dairy Council has an established maximum milk iodine level of 500 ppb. If milk iodine levels exceed this limit, the milk is considered adulterated and is unsalable.
Iodine transfer from blood into milk is very efficient, especially when supplemented in the form of ethylenediamine dihydroiodide (EDDI). The U.S. Food & Drug Administration has established a maximum limit of 49.9 mg of EDDI/day due to its high transfer efficiency into both tissue and milk compared to inorganic iodine sources.
Providing more than 1.3 ppm (DM basis) supplemental iodine in lactating dairy diets, especially when combined with improper use of iodine teat dips, sprays or backwash systems, may result in excess levels of iodine in milk (> 500 ppb). Other factors that may impact milk iodine levels include milk yield (dilution), total iodine intake and the presence of goitrogenic compounds.
With this in mind, it is recommended that producers perform periodic testing of iodine levels in milk tank samples, especially when feeding a significant amount (> 10% DM basis) of canola meal, using iodine-based teat dips or feeding diets to lactating cows containing more than 1.3 ppm iodine. This will aid in evaluating optimal iodine fortification for an individual herd.
Daryl Kleinschmit, Ph.D., is a research nutritionist with Zinpro Corporation. Contact him via e-mail at firstname.lastname@example.org.
For more information on iodine and its impact on dairy herd health, go to www.zinpro.com or talk with your nutritionist.