A small beef producer in Floyd County produces organically-certified grass-fed beef for the local health food stores and co-ops and for restaurants in the DC metropolitan area. Steer #221, a 14-month-old black Angus, shows up lame one morning; the lameness progressively worsens throughout the day. He's seen standing in the pasture, not grazing. He has a swelling in his right hindquarter and by the time the vet arrives #221 is found dead. A second steer, #216, also about 14 months old, dies 36 hours later with similar symptoms.
Postmortem examination of the dead animals reveals extensive necrosis of the leg musculature with a blackish-red discoloration with a "bubbly" appearance (left); microscopic examination of this tissue shows damage to muscle cells including extensive vacuole formation; a Gram stain is positive for a rod-like organism (right, arrows). Serum values for creatine kinase (CK) and aspartate aminotransferase (AST) enzymes are twice normal.
A discussion with the farmer reveals that a new well had recently been dug on the property to increase the water supply for his cattle, since the Spring and early Summer had been extremely dry. He also mentions that the two dead steers were "the best ones I had." A fluorescence antibody test is positive for Clostridium chauvoei. The diagnosis is acute clostridial myositis, colloquially known as "blackleg."
Points to ponder:
1. The extensive necrosis in the muscles of the trunk are caused by bacterial toxins; what accounts for the black discoloration of the affected areas? Why are CK and AST levels extremely high?
2. These were "the best animals in the herd," thrifty and rapidly gaining weight. The farmer is going to sustain a substantial loss, since they were almost at market weight and needed only a little while longer. Why would this condition likely affect rapidly-growing, healthy animals rather than older cattle?
3. The fact that a well was drilled not long before the outbreak is significant. Why?
4. What should the farmer be advised to do? If he doesn't do it, what's likely to happen?