InterdigitalNecrobacillosis (Footrot) of Cattle

Interdigitalnecrobacillosis, or footrotas it is more commonly known, is an infectious disease of cattle characterized by acute,   painful   inflammation   of  theinterdigital subcutaneous tissues of the foot. The primary bacterial agent is Fuso-bacteriumnecrophorum, which may act synergistically with Bacteroidesmelanino-genicus and other organisms, but others, such as Bacteriodesnodosus (the agent which causes ovine footrot) may also be involved.

Clinical signs are usually quite obvious and relate to the severe pain associated with the condition. The typical presentation is an acute onset of severe lameness in one or more limbs, with hind limbs being affected most frequently. The animal is usually reluctant to put any weight on the affected leg and usually holds it in a flexed position, with only the toe touching the ground. This is sometimes accompanied by a fever of 103-104T, a drop in milk production, and/or a decreased appetite. Usually the interdigital space and coronet is swollen, causing the toes to spread apart. The interdigital space often contains a fissure, with protruding, necrotic edges. Generally, there is little purulent exudatepresent, but the lesion has a very characteristic foul odor.

The organisms are thought to enter through abrasions in the epidermal layer of the foot. Uneven or stony ground and wet conditions, which soften the skin, predispose to the condition. F.necrophorum produces a leukocidalexotoxin which causes a suppurative necrosis of the subcutaneous tissue. If not treated promptly, the infection may spread to the adjacent joints or tendon sheaths and may cause septic arthritis or tenosynovitis.

This is a very commonly diagnosed foot condition, especially in damp fall and winter weather.   A recent study of the prevalence of various foot diseases in Great Britain found that footrot was the seventh most common foot condition in the summer and the fifth most common in the winter. Dairy breeds are more susceptible than beef breeds, possibly due to the more intensive condition under which they are reared. The Zebu breeds from India seem to be more resistant than other breeds of cattle. A zinc deficiency may influence susceptibility, although this connection has not been scientifically proven.

Diagnosis is usually straightforward and based on clinical signs and the characteristic gross lesions and odor. Bacterial culture of biopsy material may be helpful although lesions are often highly contaminated with fecal flora.   Although usually   not   required   for   diagnosis, histopathology reveals a dermatitis and necrosis of the skin and subcutaneous tissues.

Prompt treatment with parental antibiotics and local care for the lesion is generally very successful. The organisms are quite susceptible to most broad spectrum antibiotics.   Ceftiofur sodium (Naxcel®) was approved for treating footrot in the Fall of 1996 and is now the drug of choice, since it has no milk or meat withholding time. Procaine penicillin G,oxytetracycline, and sulfa drugs are also quite effective. Local treatment  is  beneficial   and  involves scrubbing the affected area.  All necrotic tissue should be curetted away and then the foot should be wrapped with a clean bandage. A local dressing of copper sulfate or an antibiotic ointment may be helpful. The bandage should be kept on for several days if possible.

As in most cases, prevention is the key. One mode of prevention is to smooth any rough or sharp areas in barnyards, pastures, or lanes, improve drainage of wet areas, and scrape barnyards frequently. Another preventive method is the use of a footbath. It should be of adequate size and depth to completely bathe each foot. It is recommended that it be 8' long, 2-2.5' wide, and at least 6" deep. The footbath can be placed at the exit to the milking parlor or the entrance to the pasture, so that the cows have to walk through it at least once weekly. It should be filled with a 10% copper or zinc sulfate or a 5% formalin solution. Copper and formalin solutions can be toxic if ingested. The footbath should be changed frequently to keep it clean. Alternatives to a traditional footbath (to decrease contami­nation problems), include placing a soft, thick rubber mat in the footbath, using a rinse footbath in front of the medicated one, or using a 10% mixture of copper sulfate in slaked lime. Feeding chlortetracycline to feedlot cattle also reduces the prevalence of footrot.   There are commercial vaccines available against Fusobacteriumnecro-phorum and Bacteriodesnodosus, but little information regarding their efficacy is available.

In the last several years, a much more serious condition, known as "super footrot," has been diagnosed on several occasions.   It seems to be caused by a multiple    drug-resistant    strain    of Fusobacteriumnecrophorum and causes a more rapidly progressive disease. It also seems to infect older cows more commonly. "Super footrot" is a problem to diagnose because it looks just like "regular" footrot initially.  Prompt, aggressive treatment is required to keep it from infecting the joint. Prevention of "super footrot" is also a problem, since it can occur on farms with good hygiene and regular footbathing. Using   Ceftiofur   systematically   and lincomycin or clindamycin topically is usually an effective treatment protocol.  While footrot is a common condition in cattle, most cases are highly treatable and moderately preventable. It usually will not lead to severe herd problems if treatment is prompt and effective. Delaying treatment could lead to joint involvement and create a very serious condition requiring surgical intervention.

- by: Kent L. Wolf, Class of 1998

- edited by: MelissaPopielarczyk,DVM