The term toe necrosis syndrome covers three different etiologies for a condition having a similar appearance. The three different etiopathologies are not completely understood. However, Treponema-like organisms have been isolated from all of these lesions.
Etiology and Pathogenesis:
Lesion 1–As subclinical laminitis progresses, in some cases the distal phalanx will rotate. Movement of the apex of the pedal bone will cause tearing of tissues, with resultant hemorrhage. In extreme instances, the tip of the bone will prolapse through the apex of the sole. Many cows with a rotated digit also have a ridge (the reaction ridge) running around the wall. The ridge is similar in location to a hardship groove and is displaced distally in a similar manner. Osteomyelitis of the distal phalanx can be seen in complicated cases.
Lesion 2–Many cases have been reported anecdotally in which the anterior half of the sole has been worn down almost paper thin. Hemorrhage from bruising is seen through the thin horn at the apex. Breakdown of the horn and formation of an abscess have been reported. One probable cause is a painful lesion in the heel, which forces the cow to throw most of its weight onto the anterior part of the sole.
Lesion 3–The incidence of apical necrosis can be quite high in young feedlot cattle, many of which become recumbent and die of pneumonia. The condition is sporadically reported in mature cows.
The main blood supply to the digit is the very large axial digital artery, which is vulnerable to pressure from the sharp proximal edge of the axial wall. This artery connects with the terminal arch that penetrates across the bone. Necropsy reveals that necrosis occurs distal to this artery, and radiographs tend to suggest the same thing. The terminal artery marks the margin at which pathologic fractures of the distal digit can be seen.
Necrosis of the apex of the pedal bone is extremely common in yearling beef calves after transportation over long distances. In either case, it is suspected that standing for long periods is the cause. Current laws in North America require that cattle be unloaded and watered every 40–52 hr. It is thought that long periods of standing without exercise allow the blood to pool in the feet and damage the tissues. During locomotion, the coronary cushion with the aid of venous valvules functions as a pump to return blood to the general circulation.
Treatment and Control:
Treatment is cost effective only in animals with no obvious complication. The cavity should be cleansed, dried, and packed with an antibiotic powder. If no changes occur after a few days, the lesion may be covered with methyl methacrylate. If the bottom of the lesion is black, a probe should be inserted; if necrotic tissue can be detected, 1–2 cm of the apex of the toe should be removed under regional anesthesia with hoof cutters. The condition of the pedal bone should be visible. If necrosis of the bone is confirmed, a further 1–2 cm of toe should be removed. If the wound bleeds profusely, it is likely that necrosis is not extensive. When hemorrhage is minimal, it is probable that necrosis of the bone is extensive or a physiologic fracture is present. There are several reports of the toe (not the claw) having been amputated with satisfactory recovery. Systemic antibiotics and application of a lift to the sound claw is advised. If the wound is obviously contaminated, the lesion should be packed with a hygroscopic mixture (50% magnesium sulfate and 50% glycerin) and bandaged for a maximum of 24 hr, after which the lesion should be thoroughly dried, dressed with antibiotic powder, and closed with methyl methacrylate.