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.

Diagnosis

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.

Transmission

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.

Treatment

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.

1. Foot trimming: This reduces the number of cracks and crevices where bacteria can hide, removes infected hoof, and exposes the organism to air and various medications.  All affected tissue should be trimmed away.  Many times, this involves removing a large portion of the hoof wall as well as the overgrown portion.  This is necessary if the topical treatment and oxygen are to reach the bacteria and eliminate them.  Foot trimming should be done at least one to two times per year as a part of normal management practices, and more often in conjunction with footbaths in the control of foot rot.
2. Footbaths: The most common solution commonly used in foot baths is zinc sulfate.  For treatment, foot baths should be used 1-2 times per week for several weeks.  They may also be used routinely after foot trimming and as a preventative.  Zinc sulfate (10% solution = 16 pounds in 20 gallons of water) is perhaps the most effective and least toxic bath solution.  A surfactant or wetting agent (detergent) can be added to the baths to increase their penetration into the cracks and crevices of the hoof.  Use of zinc sulfate increases their efficacy in a treatment program. When designing the foot bath area, it is important that length of contact with the solution be kept in mind.  Sufficient sized baths/soaks are necessary to handle the flock and allow sufficient contact time with the solution.  In many cases, footbath treatment effectively eliminates foot scald conditions when used in combination with practices which eliminate wet conditions/sources of the infective bacteria.
3. Dry chemicals: Zinc sulfate (dry) can be placed in a box in an area sheep must walk through. This will not treat infected animals but will help decrease the spread of the disease.  Lime, disinfectants, or drying agents may be used around feed or water troughs to reduce moisture and decrease the spread of the disease.
4. Antibiotics: Penicillin and streptomycin combinations used either as a one-shot treatment or every day up to ten days has been proven to be effective in treating foot rot.  Procaine Penicillin G or long-acting penicillin products at the same dosage may also be effective.  Single injections of long-acting tetracycline have also been successful in some cases.  Use of any of these should be after consultation with or by a veterinarian and should never be used on animals that are intended for slaughter before an adequate withdrawal time.
5. Topical medications: There are several different medications that can be applied to the hoof immediately after paring that are helpful in controlling foot rot.  Direct application of zinc sulfate solution is an option.  Other commercially available topical medications may also be applied.
6. Vaccination: Vaccines for Bacteroides nodosus are approved for use in the U.S.  The vaccine has been shown to work not only as a preventative but as a treatment as well.  Vaccination before the start of the wet season is recommended, followed by a booster each year prior to the wet season if eradication efforts have not been successful.  Abscesses are common at the injection site and therefore vaccination of show animals or animals that may be going to slaughter soon may not be practical.  As always, follow label directions carefully.  In the eradication protocol, the first vaccination may be given upon initiation of the program, followed by a second dose 4-6 weeks later.  Discuss this process thoroughly with a veterinarian to determine the best approach.

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.

Parent resources:

• Livestock Update - April 2010

Other resources in:

• Sheep & Goats

Other resources by:

• Scott P. Greiner

Other resources from:

• Animal and Poultry Sciences