PD Poll Question
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|Wednesday, 09 May 2007 08:45|
Lameness is an economically important problem in dairy cattle worldwide. Economic losses resulting from lameness arise not only from the cost to treat clinical cases but also from decreased milk production, decreased reproductive efficiency and premature culling. New York researchers estimate the average cost of lameness per 100 cows per year to be nearly $9,000.
The average incidence was 30 cases per 100 cows per year with a case fatality rate of 2 percent, involuntary culling rate of 20 percent and increase in average days open of 29 days. The National Animal Health Monitoring System (NAHMS) Dairy 1996 study revealed that 15 percent of dairy cows were culled due to lameness or injury.
The lameness caused by wartlike growths on the feet of dairy cattle has been given many names. Most commonly the condition is called hairy heel warts (HHW) while other names include, hairy foot warts, digital warts, strawberry foot, raspberry heel, interdigital papillomatosis or most accurately papillomatous digital dermatitis (PDD).
Hairy heel warts have existed for many years and were first described in Europe in the mid-1970s and then in the U.S. in the mid-1980s. By the early 1990s, many dairy operations in the continental U.S. and Canada had one or more cows afflicted with hairy heel warts.
The origin of hairy heel warts in the U.S. and factors that contributed to the rapid spread of this disease are unknown. The sale and purchase of cattle, dairy shows, hoof trimmers, nutritionists, veterinarians and any other farm visitors have been implicated in contributing to the transmission across the country. The disease is found primarily in adult dairy cattle housed in confinement facilities. The incidence is lower in dairy cattle on pasture and is rarely diagnosed in beef cattle. Hairy heel warts have been diagnosed in cattle as young as 6 months old.
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Hairy heel warts have been recognized as a significant disease, producing lameness on 40 percent of dairy operations in the Midwest. The NAHMS Dairy 1996 study also showed that 82 percent of mature cows and 86 percent of bred heifers affected by hairy heel warts displayed clinical signs of lameness. It was estimated 57 percent of all cows reported as lame were affected with hairy heel warts. This emerging disease has had a major impact on the dairy industry, resulting in a loss of productivity in lame cows.
Hairy heel warts is a superficial skin disease of the bovine. Cattle often stand on their toes and are reluctant to bear weight on their affected heels. The lesions occur most commonly on the area just above the heels on the rear feet. They are also frequently observed on the front side of the foot in the interdigital cleft extending into the interdigital space between the claws. Lesions develop fine fingerlike projections and are extremely painful to the cow. In naive cattle, even the smallest lesion can produce severe pain so that the animal is nonweight bearing in the affected limb.
Most [affected] cows prefer to lie in their stalls, rising only when necessary. This results in reduced feed intake and weight loss which calculates to a significant reduction in milk yield. One study reported a decrease in milk production by 20 to 50 percent in affected animals.
Hairy heel warts are extremely contagious. From results of tissue cultures and the evidence provided by a favorable response to antibiotic therapy, most researchers agree hairy heel warts are caused by invasion of the hoof skin with one or more bacteria, and most likely one is a spirochete organism. A major risk factor is the moisture level in the areas where cows stand.
Although lesions respond well to antibiotics initially, foot warts will frequently reoccur in animals previously treated. In a field trial performed at the University of Illinois dairy farm, a distinct breed predilection was demonstrated. While performing a topical spray trial, the rear feet of all cows were scored for severity of pain, lesion size and color. Lesion scores were more prevalent in the larger breeds.
Ninety percent of Holsteins and Brown Swiss showed evidence of foot warts, while only 19 percent of Jerseys and 45 percent of Ayrshires had lesions. Half of the Holstein cows had heel warts larger than 2.5 centimeters which produced varying degrees of pain, while 40 percent had smaller, less painful lesions. There was no difference between cows with and without foot warts when days since calving or lactation number were evaluated.
A California study surveyed dairy operations to determine the prevalence of hairy heel warts and risk factors related to the disease. Herds with more than 500 cows were more likely to have hairy heel warts than smaller herds. Herds with greater than 50 percent Holsteins had more hairy heel warts, again suggesting a possible breed predilection. Foot trimmers and foot baths were used on 87 percent of the operations with hairy heel warts.
Another California study characterized risk factors in herds with greater than 5 percent incidence compared with herds with less than 5 percent incidence. Herds with muddy corrals were 19 times more likely to have greater than 5 percent incidence compared with herds in a drier environment. Those herds that purchased replacement heifers were 4.7 times more likely to have an incidence rate of hairy heel warts greater than 5 percent compared with herds not purchasing replacements.
The therapeutic goal is to control the deep infection of the skin. Early therapeutic approaches included surgical removal with a multitude of topical salves, creams, solutions, crystals or granules. Compounds ranged from antibiotics, like tetracycline and lincomycin, to copper sulfate and iodine crystals, to more caustic substances, including muriatic acid and formaldehyde. Electrocautery and freezing were tried to remove the warts, but recurrence was commonplace.
Although labor-intensive, topical antibiotic treatment using foot wraps have been shown to provide better than 90 percent recovery rates. Bandages should be removed in three to five days. Cows should continue to be monitored since reinfection is common.
Antibacterial agents injected systemically require large doses to control the infection. Treatment with penicillin and ceftiofur at extra-label doses for three days has been highly successful but economically unrewarding when many cows in the herd are affected. In two different studies, 72 and 87 percent of cows recovered from hairy heel warts when high doses of ceftiofur were administered for three consecutive days. Injectable antibiotic therapy may be useful as an adjunct to topical treatment in selected refractory cases.
Daily, topical antibiotic or disinfectant sprays on the hairy heel wart lesions have been successful in eliminating the infection. To obtain penetration of the antibacterial agent, it is beneficial to remove the mud, manure and debris from the foot prior to any form of topical therapy.
In another study in California, cows were treated with topical Lincomycin/Spectinomycin (LS50) applied once a day for five days, followed by a two-day rest period, followed by a second five-day treatment period. Lesion scores were lowered significantly by LS50 compared with controls 90 days after treatment started.
Treatment schedules that work on one farm may not be effective on the next. Two of the most effective schedules use tetracycline or lincomycin. Mix one packet of Terramycin 343 (Pfizer) in 1 gallon of distilled or demineralized water (hard water will cause the tetracycline to precipitate).
Alternately, mix one packet of Lincomix soluble powder (Upjohn) in 2 quarts of distilled or demineralized water. Use these solutions as a topical spray at the rate of 10 to 20 cc per foot. Apply to the heels and between the toes while coating visible lesions.
This is an extra-label use of these products. Consult your local veterinarian for proper labeling and further instruction.
During the first week, treat all feet of all cows once daily for five to seven consecutive days. In subsequent weeks, continue daily topical treatment of all cows with visible lesions only.
Footbaths were originally developed to control foot rot in sheep. Zinc sulfate is a common chemical used for this purpose. When these footbaths are used effectively, sheep are paraded through one at a time. The sheep have little time to defecate in the foot bath and contaminate the solution. Some researchers have questioned the efficacy of footbaths for hairy heel wart control because they become manure slurries after multiple cow passages. Footbaths with 5 to 10 percent copper sulfate or 1 to 10 grams per liter tetracycline have been moderately successful in controlling the disease.
To achieve these concentrations add 5 to 10 pounds of copper sulfate in 8.5 gallons of water or one packet of Terramycin 343 (Pfizer) in 25 gallons of water (1 gram per liter). Footbath schedules range from daily soaks, to twice weekly, to each month for three to four days.
It is recommended the foot bath be placed in the return alleys, not in the parlor. Dirt and manure should be washed off the cows’ feet prior to walking through the footbath. The solution in the footbath should be changed when grossly contaminated or after no more than 150 cows have passed through it.
Dairy producers usually prefer to use footbaths to control hairy heel warts because they requires less labor. Assuming labor costs are $10 per hour, we can compare the cost to maintain two 50-gallon footbaths (one for each side of the parlor) to topical spray treatment program on a 150-cow dairy. Each footbath could be used for two milkings (75 cows each side, twice a day) before refreshing. It would require four packets of Terramycin (at $12 each) to charge both footbaths for one day.
Three consecutive daily footbaths with one hour of labor each day would cost $174 or $58 per day. Increasing the concentration in the footbath to 5 grams per liter would increase the cost to $750 or $250 per day. The same number of cows could be treated by topical spray at 25 grams per liter tetracycline for $42 per day (three hours of hired labor per day, $12 for tetracycline). PD
—From Louisiana Dairy Digest, December 2006