Digital dermatitis in dairy cattle cannot be eliminated. It can only be controlled. And that control ought to start with dairy heifers. That was the gist of the message from University of Wisconsin-Madison veterinarian and foot health specialist Nigel Cook to attendees at the Extension Service’s 2015 dairy cattle hoof care seminar.
Cook credited two years of research by UW-Madison doctoral student Arturo Gomez for leading to “a change of focus” on when digital dermatitis and other foot diseases should be diagnosed and treated. That study, which tracked 640 dairy heifers from just after breeding age to the end of their first lactation, found a 20-30 percent infection rate before calving — a rate that carried over into the lactation.
Too late to treat
The findings by Gomez prompted Nigel to declare that “it’s too late” to start noticing this problem and treating it only with cattle that are already in the milking herd. “It’s a massive problem,” he stated. “It can be controlled but not eliminated.” Digital dermatitis, which is commonly referred to as hairy warts, along with white line disease and sole ulcers, are responsible for having an average of 25 percent of dairy cows being lame at any given time, Cook pointed out. Cook stressed that it is crucial to detect and treat digital dermatitis at its M2 or acute stage with at least weekly observations of the cows that exhibit any sign of lameness. Providing treatment at the M4 or chronic stage of infection “is a waste,” he remarked.
First specifically identified by the University of California-Davis, digital dermatitis has spread across the world, Cook noted. “There are very few feet that are pure now.” Digital dermatitis has become common in facilities with concrete floors where cattle are confined, Cook observed. How virulent it becomes on a particular farm depends on which of the many types of bacteria in the treponemes family are present there, he explained. Those bacteria or pathogens, which come from the rumen and are always present in manure, have several life cycle stages, Cook indicated. They thrive in wet manure, less so in dry manure, he noted.
The infectious bacteria enter a cow’s foot or hoof through breaks in the skin, Cook pointed out. From there, the severity of the case of infection depends on how deep the bacteria move into the adjacent tissue. What the infection ultimately does is to disrupt the normal natural pattern of cell growth, resulting in the physical breakdowns that cause lameness, Cook explained. He pointed out that there are trace minerals that help cows to cope with the early stages of the infection and to reduce the likelihood of an acute or chronic case of digital dermatitis. “Cure rates are very poor at the M4 stage,” Cook emphasized. “M4s are a ticking time bomb. They could cycle back to become M2s (acute). That’s why it is so difficult to eliminate digital dermatitis. An M1 can naturally cure but an M2 will not.”
Although Europe has sprays that are licensed for the treatment of digital dermatitis, there are no labeled therapies (antibiotic products) in the United States for that purpose, Cook reported. This restricts the treatment to extra label use approved by a veterinarian, he explained. Among the many possible products, Cook likes oxytetracycline and notes that it will be the only choice after January 1, 2017 under the Veterinary Feed Directive from the federal Food and Drug Administration. As part of that protocol, the extra label treatment will be available only in conjunction with a valid client patient relationship (VCPR) between the farm and veterinarian, he emphasized. Cook mentioned dosage treatments of 2,000 milligrams of oxytetracycline powder or 10 centimeters of LA-200 (Liquamycin from Zoetis) as topical applications. For the treatment, he suggests at least a single wrap bandage so the product application will be somewhat protected. The bandage should not be left on for more than two days, he indicated.
A restriction will also be in place with all anti-microbial products that are also used to treat humans, Cook reported. He said the limitations on use with dairy cows arise from a concern about residues in milk, especially with any milk that would be used to dairy products going into the export market. Based on recent tests that Cook described, milk should be withheld for 24 hours after such a treatment in order to avoid the possibility of violating the residue limits. On that point, he said the risks are highest with treating a few cows in a relatively small herd because of the relevance of the dilution factor. He said no research data is available on any potential residue risk in meat from such treatments. Another restriction with tetracycline will be that veterinarians will not be allowed to carry it in their vehicles, Cook indicated. This means that any supply would have to be available on the farm, he said.
In the wake of the restrictions, it would not be surprising if the commercial sector offers a number of alternatives, Cook predicted. Before using any of them, insist on having research that backs their efficacy, he advised. Be sure to avoid the acids that might be included in a new group of products, Cook continued. He explained that they could easily cause more damage on infection sites where the skin is gone and there is likely to be bleeding. One exception that Cook mentioned is the possibility of a solicylic acid for treatment of M4 but not M2 stage infections. Another possible product, for which records need to be kept, is the Intra Hoof-Sol gel, he said. No effective vaccine is available for deterring digital dermatitis, he noted.
Foot bath considerations
A foot bath could well be helpful in keeping M4 chronic infections from reverting to the acute M2 cases but the use of acids in the solution is very risky, Cook stated. For that reason, he prefers copper sulfate as the solution ingredient and strongly suggests that the pH of the solution not be much lower than 3.5.
Cook is concerned about an apparent increase of the use of acids in foot baths. Instead of changing ingredients, lengthen the distance of the foot bath, have it available three to four days a week, and try to limit the use of a batch of solution to about 150 cows because of the potential buildup of bacteria in it, he advised. Compared to the actual number of having 15-25 percent of a herd’s cow having an M2 infection at some time, Cook sets a goal of keeping that percentage to less than 10. On a related point, he fears that genetic selections (Type III cows) to increase milk production might, unfortunately, be linked to inherited traits making those cows more vulnerable to digital dermatitis infections.
Cook acknowledged that a weekly rather than monthly check of one’s dairy cattle is “another job” that requires time and labor on the farm. He believes, however, that it is justified by such research numbers as an average loss of 740 pounds of milk production due to an infection during the first lactation in addition to dire effects on the number of open days and the reproduction timetable. Hoof trimmers can play a very beneficial role in coping with digital dermatitis, depending on the quality of records they compile and on what kind of treatments they give, Cook commented. He pointed out that digital dermatitis causes hoof formation changes, which enable the infected lesions to survive longer and become more severe. Trimming, which addresses the hoof changes induced by the disease, will be very beneficial, Cook suggested. Beyond that, he said the best way to cope with digital dermatitis is to improve the cleanliness of the environment in which the infectious bacteria survive and thrive.
By: Ray Mueller