Since the 1960's, iodine topical germicides have been used as teat dips for the prevention of mastitis in dairy cows. These products are typically iodophor solutions with the iodine complexed or solubilized by a nonionic surfactant. Early products typically contained 0.5% or 1% available iodine because lower level iodine products were not adequately stable. Products with lower levels of iodine were made available in the early 1980's when technology to provide proper stability was developed. Iodine is the active ingredient in 65-70% of the teat dips sold in the United States and 55-65% of teat dips sold globally.
Iodine is the preferred germicide for a teat dip because of its desirable properties: broad spectrum of kill, excellent stability, mildness to skin, and no residue concern. A variety of iodine products have been demonstrated to be effective as shown by the NMC Teat Dip Bibliography (1). However, Pankey, et al, have shown that there is a wide range of efficacy for iodine teat dips (2). In that study, germicidal efficacy ranged from 1.93-3.53 log reduction for Staph. aureus and 1.83-4.24 for E. coli. The efficacy was not correlated with the titratable iodine level. In addition to titratable iodine level, a variety of formulation variables affect the efficacy of iodophor teat dips. These include: free iodine, pH, wetting ability, viscosity, solvent, emollient content, and type or amount of iodine complexing agent.
Of the variables affecting the efficiency of iodine based teat dips, free iodine is probably the most critical. Free iodine is defined as the uncomplexed iodine. Iodine is soluble in water up to 300 ppm (0.03%). To achieve a higher solubility, iodine must be complexed or solubilized by iodide, a nonionic surfactant, polyvinylpyrrolidone, or a solvent such as alcohol. Only iodine that is uncomplexed is considered to be free iodine. Free iodine exists in equilibrium with complexed iodine. The concentration of free iodine in iodophors is controlled by a variety of variables including: iodine to iodide ratio; surfactant to iodine ratio; type of surfactant; concentrations of iodine, iodide and surfactant; pH; temperature; and the age of the product. Over the life of a product, the free iodine content will typically decrease due to: reaction with surfactants or emollients, decomposition to iodide and iodate, and migration through plastic containers. The effect of free iodine on efficacy of iodine germicides was shown by Wyss in 1944 (6). He demonstrated that the time to achieve 99% kill of B. metiens spores was directly related to the free iodine concentration of the germicide (Table 1).
Table 1 The effect of free iodine on killing time for B. metiens spores
| Titratable Iodine (ppm) |
Free Iodine (ppm) |
99% Killing Time (minutes)B. metiens Spores, pH 7.0, 25°C |
|
40 |
0.2 |
220 |
|
40 |
2.3 |
39 |
|
40 |
15.1 |
9.5 |
|
40 |
36.8 |
4.3 |
|
10 |
5.4 |
20.5 |
Gottardi(7) has similarly shown the impact of free iodine on S. aureus inactivation (Table 2) for iodine products with varying titratable and free iodine levels. In this study, a germicide with as little as 102 ppm of titratable iodine and elevated free iodine was more effective than one with 10,000 ppm titratable iodine (Betadine).
Table 2 Inactivation of S. aureus suspended in 10% porcine serum at 20°C
| Titratable Iodine (ppm) |
Free Molecular Iodine )
(ppm) |
Time to Achieve 6-Log Reduction of S. aureus (seconds |
|
280 |
175 |
15 |
|
216 |
128 |
60 |
|
152 |
85 |
60 |
|
102 |
47 |
90 |
|
45 |
20 |
240 |
|
10,000 |
4.6 |
240 |
The effect of free iodine on teat dip performance has been demonstrated in both lab microbiological experiments and NMC Challenge protocols. In the laboratory, the A.O.A.C. Germicidal Detergent Sanitizing Action Test(8) has been used to show the importance of free iodine. In one test, a 0.05% available iodine teat dip with 75 ppm free iodine was shown to be more effective than 0.25-1.0% iodine products with free iodine levels between 2-3 ppm (Table 3). These teat dip products were iodophors that contained nonylphenol ethoxylates as the complexing agents.
Table 3 A.O.A.C. germicidal detergent sanitizing action test1
|
|
|
Products |
|
|
|
|
A |
B |
C |
D |
| Free Iodine |
Ppm |
75 |
2.5 |
2.0 |
2.0 |
| Available Iodine |
% |
0.005 |
0.5 |
1.0 |
0.25 |
| % Reduction |
5 sec. |
99.999 |
94.500
|
83.750 |
31.724
|
| Staph. aureus |
15 sec. |
99.999
|
99.890 |
97.675
|
92.413 |
| 10% Milk Challenge |
30 sec. |
99.999 |
99.995 |
99.999 |
99.172
|
1Testing was completed at 25°C with a 10 minute challenge with 10% milk prior to inoculation of the teat dips with the bacteria.
This study shows that products with elevated free iodine are more effective than products with low free iodine, even when the available iodine level is 10 to 20 times greater.
In vitro studies were conducted on two 0.1% iodine teat dip compositions with free iodine levels of 5.5 and 3.0 ppm. The formulations were based on ethyleneoxide-propylene oxide copolymer nonionic surfactant iodine complexors. Log reductions were determined for E. coli and Staph aureus at 25°C (Table 4). Product samples were neutralized after 15 to 120 seconds to determine efficacy. The higher free iodine formulation showed better efficacy against both organisms. The difference in efficacy between the higher and lower free iodine compositions was larger at the lower temperature.
Table 4 Effect of free iodine and temperature on the reduction of Staph. aureus and E. coli
|
|
|
|
|
Log Reduction |
|
|
| Titratable Iodine |
Free Iodine |
Temperature (°C) |
Organism |
15
sec. |
30
sec. |
60 sec. |
120
sec. |
| 0.1 |
5.5 |
25 |
E.Coli |
7 |
7 |
7 |
|
| 0.1 |
3.0 |
25 |
E.Coli |
5.7 |
7 |
7 |
|
| 0.1 |
5.5 |
20 |
E.Coli |
5.9 |
7 |
7 |
|
| 0.1 |
3.0 |
20 |
E.Coli |
2.6 |
5.4 |
7 |
|
| 0.1 |
5.5 |
25 |
Staph.aureus |
|
7 |
7 |
7 |
| 0.1 |
3.0 |
25 |
Staph.aureus |
|
<2.3 |
4.2 |
7 |
| 0.1 |
5.5 |
20 |
Staph.aureus |
|
7 |
7 |
7 |
| 0.1 |
3.0 |
20 |
Staph.aureus |
|
<2.3 |
<2.3 |
5 |
The importance of free iodine level has also been demonstrated using NMC Challenge Protocols. In one study, an 0.05% available iodine, 70 ppm free iodine product (12) was compared with an 0.5% available iodine, 2 ppm free iodine product. A pre-dip challenge trial was run by dipping the teats with Strep. uberis one hour prior to milking. A post dip challenge protocol was run with Staph. aureus and Strep. agalactiae in accordance with the published procedure. Results for this trial support the importance of free iodine levels in teat dips for preventing mammary infections (see Table 5).
Table 5 NMC challenge protocol
|
|
Reduction |
|
|
Titratable |
Free |
Post Dip |
Pre-Dip |
|
Iodine |
Iodine |
Staph. aureus & Strep. agalactiae |
Strep. uberis
|
|
0.5% |
2 ppm |
67.5% |
60.3%
|
|
0.05% |
70 ppm |
75.0% |
67.9% |
In a second NMC challenge protocol trial, two products having 0.25% available iodine were tested using both pre- and post-dip challenge applications. The two formulations were both based on nonionic surfactant iodine complexes but differed in the free iodine level. See Table 6 below. The formulation with elevated free iodine (13) provided 57.6% reduction in new intramammary infections compared to the low free iodine formulation (9).
Table 6 NMC challenge protocol
|
TOTAL |
|
|
|
|
TREATMENT |
INFECTIONS |
QUARTERS |
REDUSTION |
|
|
NEGATIVE CONTROL |
74 |
61.6% |
-- |
-- |
|
CONVETIONAL YECHNOLOGY IODINE |
38 |
31.6% |
48.6 % |
-- |
|
ELEVATED FREE IODINE |
70 ppm |
15.0% |
75.6% |
57.6% |
Teat condition studies have been conducted on a variety of products with elevated free iodine (10)(11). These studies have shown that when properly formulated, products with high levels of free iodine do not cause skin irritation problems.
References:
Summary of Peer-Reviewed Publications of Efficacy of Pre-milking and Postmilking Teat Disinfectants (Published Since 1980), NMC 37th Annual Meeting - 1998; 350-363
Pankey, J.W., P.A. Murdough, Evaluation of 57 Teat Sanitizers (1993); JDS, 76:2033-2038
Gottardi, W., Potentiometric Evaluation of the Equilibrium Concentrations of Free and Complex Bound Iodine in Aqueous Solutions of Polyvinylpyrrolidone-Iodine (Povidone-Iodine) (1983); Analytisch Chemie, 314:582-585
Allawala, N.A., S. Riegelman, The Properties of Iodine in Solutions of Surface-Active Agents (1953); JAPA, Vol. 42, No. 7, 396-401
Winicov, M., E.L.Winicov, Determination of Free Iodine and Its Significance in Povidone-Iodine Solution (1983), International Symposium on Povidone, Lexington, Kentucky
Wyss, O., F.B. Shandshov, The Germicidal Action of Iodine (1944)
Gottardi, W., et al., Control of the Amount of Free Molecular Iodine in Iodine Germicides (1997), J. Pharm. Pharmacol; 49:1195-1199
Helrich, K., ed., Official Methods of Analysis of the Association of Official Analytical Chemists (1990), 138-140; Published by the Association of Official Analytical Chemists, Inc., 2200 Wilson Boulevard, Suite 400, Arlington, VA, 22201, USA
Galton, D., personal communication
Hemling, T.C., M. McKinzie, Efficacy of Concentrated Powdered Teat Dip Giving Elevated Levels of Free Iodine (1995); poster, NMC
McKinzie, M., T.C. Hemling, Evaluation of a New Barrier Teat Dip Containing 1% Titratable Iodine (1996); poster, NMC Annual Meeting Proceeding
IodoZyme®, West Agro, Inc
Della Care®, DeLaval, Inc. |