A wet winter, coupled with early spring rains and warm weather have set up ideal conditions for sheep producers to deal with the menacing challenges of foot problems. The two most common of these are foot rot and foot scald. While similar in the fact that both are contagious and cause lameness and decreased production, there are some distinct differences between the two diseases. Foot rot is caused by an interaction of two anaerobic (without oxygen) bacteria, Bacteroides nodosus and Fusobacterium necrophorum. Fusobacterium necrophorum is a normal inhabitant of the ruminant digestive tract and in wet weather may interact with another bacteria, Corynebacterium pyogenes, to produce foot scald, an infection of the skin between the toes. This infection sets up the foot for invasion by Bacteroides nodosus, which, working in conjunction with the Fusobacterium, produces the condition known as foot rot. Since Bacteroides can only live in the hoof of an infected animal or in the soil for no more than 10-14 days, it is possible through careful management procedures, to keep from introducing foot rot into a flock and to successfully control and/or eliminate the disease if the flock is infected.
Lameness is usually the major sign of an infected animal, although sheep with an early infection may not exhibit lameness. The area between the toes first becomes moist and reddened. Then the infection invades the sole of the hoof, undermining and causing separation of the horny tissues. The infection causes a characteristic foul odor and may infect one or more feet at the same time. Foot scald is confined to the skin surface between the toes, which becomes moist and irritated.
The bacteria that causes foot rot is spread from infected sheep to the ground, manure, bedding, etc. where it is then picked up by non-infected sheep. Foot rot is typically introduced by purchase of an infected animal. Favorable environmental conditions (warm temperature, moisture) facilitate the spread of the infective organisms. Since the organism doesn't survive long in the environment (< 2 wks), carriers in the flock will continue to reinfect the flock unless the animal is either culled or the organism is eliminated by proper treatment. Warm, wet weather, irritation to the skin between the hooves, and overgrown hooves are predisposing factors. These factors, in combination with the presence of infective bacteria, lead to foot rot in sheep.
The control of foot rot is based on several management practices that decrease predisposing factors, and on the treatment and immunization of infected and susceptible sheep. The best results are obtained when several of the following methods are combined.
Using combinations of these procedures, foot rot can be eradicated. However, the best strategy is to practice good flock biosecurity and prevent introduction. Studies have shown eradication is possible using combinations of treatment programs. While no single treatment is highly effective alone, treatment protocols that include foot trimming along with foot bath regiment and vaccination are most effective.
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Issued in furtherance of Cooperative Extension work, Virginia Polytechnic Institute and State University, Virginia State University, and the U.S. Department of Agriculture cooperating. Alan L. Grant, Dean, College of Agriculture and Life Sciences; Edwin J. Jones, Director, Virginia Cooperative Extension, Virginia Tech, Blacksburg; Jewel E. Hairston, Administrator, 1890 Extension Program, Virginia State, Petersburg.
March 29, 2010