Digital Dermatitis in Cattle
Digital dermatitis is the most common disease of the feet of mature dairy cattle and is endemic in intensively managed dairy operations worldwide. It tends to mask or overshadow other more painful lesions present concurrently. Incidence is low in pastoral settings such as in New Zealand and Chile. The presence of the disease in beef cattle appears to be minimal.
Two main types of lesions are seen. The erosive/reactive form is seen more commonly in Europe, whereas the proliferative or wart-like form is more prevalent in North America. Both forms cause varying degrees of discomfort and may give rise to severe lameness. Both forms can be seen in the same animal. The two forms likely represent different stages of the same disease process.
Explosive outbreaks can occur when affected cows are introduced to previously unaffected herds.
Treponema-like organisms can be observed in microscopic samples isolated from most lesions. However, the number of strains of Treponema affecting cattle can be as high as 80, some of which may be oral or rectal. It would be wise not to incriminate just one strain as the cause because of the numerous manifestations of digital dermatitis. Digital dermatitis is likely to be polytreponemal (eg, T phagedenis, T vincentii, and T denticola).
Digital dermatitis is much more prevalent if hygiene is poor and the feet are exposed frequently to slurry. It is widely believed that a number of predisposing bacteria are involved. It has been postulated that the once ubiquitous Dichelobacter nodosus may be an important synergizing agent; Campylobacter spp and Prevotella spp may also be involved in the etiology.
Skin maceration and the presence of a semi-anaerobic environment are important predisposing factors. Many treponemes are found in the deeper layers of the epidermis, some of which are believed to reach these layers of the epidermis via hair follicles.
A relatively weak immune response has been detected in naive cattle.
Lesions are most common in the region of the flexor commissure of the interdigital space. Less typically, lesions have been seen on the dorsal surface of the foot as well as around the dewclaws. One or both hind feet are most commonly involved, although forefeet can be affected. Lesions vary considerably in size and appearance both within a herd and in different parts of the world.
The following system has been developed to classify the stages of this disease: M0 = normal skin; M1 = early, small circumscribed red to gray epithelial defects of <2 cm in diameter preceding the acute stage, appearing between acute episodes or within the margins of a chronic M4 lesion; M2 = acute, active ulcerative (“strawberry-like”) or granulomatous (red-gray) lesions >2 cm in diameter and sometimes surrounded by white halo-like tissues, which may be slightly papillomatous; M3 = the healing stage occurring within 1–2 days after topical therapy, with the lesion covered with firm, scab-like material; M4 = the chronic stage in which the epithelium is thickened and/or proliferative (filamentous or scab-like) and several centimeters in diameter.
Acute lesions are initially treated topically. The lesion should be scrubbed clean with a stiff brush and soapy water, rinsed, and dried. An antibiotic powder such as oxytetracycline is applied and protected by a gauze pad or a small feminine hygiene pad held in place by a waterproof bandage or a reinforced nylon device (booties) that can be affixed with hook-and-loop-tape closures. Multiple treatments are usually necessary. Oxytetracycline treatment has not resulted in detectable residual levels of the antibiotic in blood or milk. Extremely high parenteral antibiotic dosages have been reported to help resolve severe lesions.
Once a lesion has started to heal, topical dressings may be sprayed on with a pressurized backpack spray unit. Soluble oxytetracycline or lincomycin-spectinomycin (66 g and 132 g/L of water, respectively) produces the best results. Contamination of the lesion must be avoided at this stage. Although apparent resolution can be achieved, recurrence seems almost inevitable, and farmers should be so advised.
There are no effective vaccines. The following methods are used in control: 1) Automatic power washing of the feet with soapy water before entering the milking parlor. 2) Passage through a medicated footbath after passing through the milking parlor with a 30-min drainage period. 3) Diligence in ensuring the environment is regularly freed from slurry and liquid contamination. 4) If digital dermatitis is not present, replacement animals should not be introduced and the herd should not be exposed to vectors such as unsterilized instruments or visitors’ dirty boots.