Causes of Foot Rot
Foot rot is caused by bacteria invading damaged soft tissue of the interdigital space (between the toes). Damage to the soft tissue between the toes can occur from abrasions from rocks, stubble, or frozen/dried mud or continuous exposure to wet conditions (wet manure and mud) which will cause softening and thinning of the interdigital skin. Damage to the tissues of the feet will cause susceptibility to the bacteria that causes foot rot.
Fusobacterium necrophorum, a common bacteria, is the causative organism of foot rot but other bacteria also have been implicated to work synergistically with F. necrophorum. The majority of F. necrophorum isolated belong to one of two types (types A or B) which produce toxins that cause necrosis (death) or decay of the infected tissues. It is important to remember though the organism cannot penetrate intact, healthy skin.
Interestingly, F. necrophorum is also isolated from liver abscesses in feeder cattle, necrotic stomatitis in calves, and calf diphtheria. F. necrophorum appears to act cooperatively with other bacteria, such as Bacillus melaninogenicus, Staphylococcus aureus, Escherichia coli, and Actinomyces pyogenes, thereby decreasing the infective amount of F. necrophorum necessary to cause disease.
Course of the Disease
Regardless of the source once loss of skin integrity occurs, bacteria gain entrance into subcutaneous tissues and begin rapid multiplication and production of toxins that stimulate further continued bacterial multiplication and penetration of infection into the deeper structures of the foot.
Symptoms of Foot Rot
The first signs of foot rot, following a growth and development period of the organism for a period of five to seven days, are lameness, acute swelling of interdigital tissues, and swelling evenly distributed around the hairline of both hooves. Eventually the interdigital skin cracks open, revealing a foul-smelling, necrotic, core-like material. Untreated, the swelling may progress up the foot to the fetlock or higher. More importantly, the swelling may invade the deeper structures of the foot such as the navicular bone, coffin joint, coffin bone, and tendons.
Diagnosis of Foot Rot
Diagnosis of foot rot can normally be made by examining the foot, looking at the characteristic signs of sudden onset of lameness (usually one foot), elevated body temperature, swelling between the digits (toes), and separation of the interdigital skin (skin between the toes).
A potential problem is that there are other conditions that can cause lameness in cattle and can be mistaken for foot rot and would require different treatment. These include: interdigital dermatitis, sole ulcers, sole abscesses, sole abrasions, infected corns, fractures, septic arthritis, and inflammation or infection of tendons and tendon sheaths, all of which generally only involve one claw of the foot and not the areas of skin or soft tissues between the toes or claws.
- Digital dermatitis (hairy heel warts) is often confused with foot rot because of foot swelling and severity of lameness. Digital dermatitis affects only the skin, beginning in the area of the heel bulbs and progressing up to the area of the dewclaws; whereas, foot rot lesions occur in the interdigital area and invade the subcutaneous tissues.
- Cattle grazing endophyte infected fescue pastures that develop fescue toxicity, causing loss of blood circulation to the feet and subsequent lameness, are sometimes mistaken as having foot rot.
Treatment of Foot Rot
Treatment of foot rot is usually successful, especially when caught and started early in the disease course. Treatment should always begin with cleaning and examining the foot to establish that lameness is actually due to foot rot and not one of the other conditions discussed. At this point, a topical treatment of your choice should be applied. Some very mild cases will respond to topical therapy only. Most cases require the use of systemic (injectable) antimicrobial therapy.
The disease can become chronic, with a poorer likelihood of recovery if treatment is delayed, resulting in deeper structures of the toe becoming affected. Weight gain is significantly reduced when grazing cattle contract the disease. Foot rot is usually sporadic in occurrence, but the disease incidence has been reported as high as 25% in high-intensity beef or dairy production units. Approximately 20% of all diagnosed lameness in cattle is actually foot rot.
If at all possible, affected animals should be kept in dry areas until healed. If improvement is not evident within three to four days, it may mean the infection has invaded the deeper tissues. Infections that do not respond to initial treatments need to be re-evaluated by your veterinarian soon rather than later.
When cattle are moderately to severely deficient in dietary zinc, supplemental zinc may reduce the incidence of foot rot. Improvements have been seen in foot health even when zinc is not deficient in the diet when organic sources are included and overall zinc concentrations in supplements are increased. Zinc is important in maintaining skin and hoof integrity; therefore, adequate dietary zinc should be provided to help minimize foot rot and other types of lameness.
This article also appeared in Mid-America Farmer Grower, December 8, 2014