Solving mysteries of multiple deaths
Every once in a while, a large animal veterinarian gets one of those calls that we dread. It is the call that there are multiple dead animals to an unexplained cause. Such situations can result in disaster for the farmer if the cause of death isn't soon discovered.
Fortunately, these situations are pretty uncommon, but when they come in, prompt action is of utmost importance. Earlier this year, we took a call from a client who said he had a heifer die suddenly and wanted a necropsy performed on her. A necropsy is analogous to an autopsy on a person, except that the term autopsy is reserved for humans.
So, after the call came in earlier this year to necropsy a heifer, it was put to the end of the line. After all of the sick animals had been taken care of and as I was preparing to drive to the farm to perform the necropsy, the farmer called again to tell us to be prepared for two of the procedures.
My anxiety level immediately rose about tenfold. Now there are two dead heifers that were apparently normal yesterday. It would be a rare coincidence to have two dead animals in the same day from different causes. This must be an outbreak, I thought.
There are a handful of common conditions that will cause sudden death in cattle and whenever I'm called to investigate the cause, I like to review them in my head. Bloat, electrocution, grass tetany, blackleg and hardware disease are probably the most common in this area. As I was thinking, I recalled that one of my partners had looked at a heifer at the same farm earlier in the day that couldn't stand up. I had assumed that she was the animal to have died first, but she wasn't. She was actually the second. Immediately, I was concerned about blackleg, but I tried to be careful not to bias myself before doing a thorough investigation.
Blackleg is a disease caused by a group of bacteria called Clostridia. For reference, the bacteria that cause both tetanus and botulism belong to the Clostridium genus. These Clostridia bacteria are abundant in the environment as their function is to break down and decay dead tissue and organic matter. These bacteria can live inside the digestive tract of mammals and rarely cause harm. Under certain conditions, however, they produce potent toxins which are responsible for the diseases they produce.
Blackleg is not exactly rare, but it tends to affect only young stock. Our practice sees a few cases a year, both in beef and dairy cattle. There is a commercial vaccine for the disease and is almost always effective at preventing the disease. This herd, unfortunately, was not vaccinated.
When I arrived at the farm, both heifers were readied for the necropsy. A full necropsy requires a complete examination of both the chest and abdominal cavities. In this case, however, a complete necropsy exam wasn't necessary as the diagnosis was obvious by examining just the leg muscles. Even before I made my initial cut with my knife into the first animal, I felt the characteristic air under the skin over the animal's back.
Clostridia bacteria have a tendency to produce gas whenever and wherever they are growing. When this happens in an animal, either alive or dead, it results in the tissues feeling like bubble wrap when pressed on. One can easily feel the gas through the skin. As I prepared to make my initial cut for the necropsy, it seemed as though this was going to be a straightforward case of blackleg. What followed that night was far from typical.
(To be continued next Tuesday)