Environmental risk factors for infectious causes of lameness
1. Foot rot is caused by specific pathogenic strains of Fusobacterium necrophorum and Bacteriodes melaninogenicus that gain entry through the interdigital skin. These bacteria can persist in wet soil or slurry for very long periods. They
are also routinely present in the rumen and colon of cattle, although not necessarily pathogenic strains. Intact dry skin
is resistant to penetration of these organisms. Thus, conditions that produce breaks in the interdigital skin such as coarse
sand or small stones becoming lodged in the interdigital space by walking through mud may predispose to foot rot. These conditions
might prevail in cattle laneways, around water sources, or in riparian zones. Traditional control methods have been to fence
cattle away from riparian zones and mudholes. A new approach for cattle laneways that is in use in the United Kingdom was
recently described by Dr. Roger Blowey from Gloucester. A 40 inch wide roadway is constructed by excavating to a depth of
12 inches. Eight inches of gravel or crushed stone is placed in the trench, covered with geotextile fabric and the remainder
of the excavation filled with shredded bark. The laneway remains dry on the surface, stands up very well to traffic, and cows
move quite comfortably along.
Foot rot in housed dairy cattle may be predisposed by the maceration of the interdigital skin which is continuously moist.
The severity of problems in housed dairy cattle is dependent on manure removal practices which may influence both the infection
pressure and the interdigital skin integrity. Footbathing with antibacterial compounds is a routine procedure to prevent new
cases of foot rot.
2. Interdigital dermatitis is a chronic superficial infection of the interdigital skin caused by Dichelobacter nodosus. It is very common in housed cattle with visible lesions present in the majority of cattle, whether housed in freestalls
or tiestalls. One reference indicates a lower incidence of lameness due to interdigital dermatitis on slatted floors than
solid floors. Pain and lameness are not present in the most obviously infected cattle. Exposure to manure and urine predispose
to infection and to the severity of problems. Most lameness due to interdigital dermatitis is secondary either to skin (and
possibly hoof sole) hypertrophy or to fissures in the heel horn caused by the bacterial elastases that are capable of cleaving
the beta-pleated keratin of the hoof. The main environmental risk factors seem to be manure contact with the skin and anaerobic
conditions between the manure layer and the skin. Control is as for foot rot.
3. Digital dermatitis is an infectious disease of the skin affecting cattle older than about 6 months of age anywhere from the
vicinity of the dewclaws distally. The causal organism(s) have not been conclusively identified but response to therapy with
antibacterial drugs and the consistent observation of spirochetes in affected tissues supports a bacterial etiology. Environmental
risk factors are the same as for interdigital dermatitis and the 2 diseases often occur together with some synergy apparent.
Infection with Dichelobacter nodosus may facilitate establishment of the agents of digital dermatitis. Dry conditions as might occur in dry lot or some pasture
conditions seem to prevent spread of the infection but do not influence the severity in already infected cattle. Control is
with footbathing or spraying with the antibiotics (oxy)tetracycline or lincomycin. These plus some antiseptic solutions including
formalin are used successfully in footbaths for control.