Lameness is one of the most common conditions in adult dairy cows. Many types of lameness are not contagious but digital dermatitis is caused by bacteria and is contagious. Because lame cows are also more likely to have their feet trimmed, there has been concern that foot trimming might inadvertently spread digital dermatitis.
There is research evidence that hoof knives can become contaminated with some of the bacteria that cause digital dermatitis. There is also research to show that some common disinfectants should be able to kill the bacteria that cause digital dermatitis even if they are used when the disinfectant is contaminated to a certain extent with manure.
Since research already showed that disinfectants can kill the digital dermatitis bacteria in a laboratory, a logical next step is to figure out if disinfectants would work when they are used on the hoof knives themselves. That is what researchers in the United Kingdom did.
They contaminated the surfaces of hoof knives with two of the bacteria that are known to cause digital dermatitis. Then they checked to find out if the bacteria were still on the knives for up to 18 hours later. They also checked to see if 20 seconds of exposure to any of five different disinfectants killed the bacteria on the knives.
They found that the bacteria survived on the surface of the hoof knives at 10 minutes, 1 hour and 2 hours but, when they checked at any of the later times (4 and 18 hours), they could not find bacteria. So bacteria can survive on actual knife surfaces for long enough that they can spread that bacteria to other cows. To know for sure, you’d need to actually test the risk of spread using contaminated knives.
They also found that 20 seconds of exposure to 3 of the 5 disinfectants they tested was effective in eliminating the infection from the surface of the hoof knives. One of the disinfectants that they found to work was Virkon. They mixed it at 2 % weight of Virkon to the appropriate volume of water. Virkon is readily available in Canada.
Another disinfectant they found to be effective was an iodine-based product that does not appear to be available in Canada.
The third disinfectant that they found was able to eliminate the bacteria from the surface of the hoof knives was a 2 % solution of sodium hypochlorite. Sodium hypochlorite is the compound that is commonly called ‘bleach’ — you’d need to make sure that the strength of the bleach matches the strength that was tested (2 %).
Two of the 5 disinfectants were not effective in completely neutralizing the bacteria on the hoof knives. One was a 5 % solution of copper sulphate. The other was a 2 % solution of glutaraldehyde. There are several veterinary products sold in Canada that contain copper sulphate and glutaraldehyde, although not necessarily at the same concentrations as the disinfectants tested in the research trial.
You can only rely on disinfectants to work if they are used properly. There are a few points to note about this research that would likely affect how well the disinfectants would work in ‘the real world.’ All the knives were clean when they were disinfected; manure on the knife could weaken the disinfectant. Disinfectants take time to work. The researchers left each of disinfectants on the knives for 20 seconds — that may not seem like much time but it can seem like an eternity if you’re doing that between feet and between cows. Lastly, pretty much every disinfectant is also corrosive to metal and represents some sort of human health hazard so take appropriate care of the equipment, the cows and the people involved.
Dr. Rob Tremblay is a veterinarian for Boehringer-Ingelheim and lives near Guelph. Follow his blog at http://bovinehealth.ca.