Veterinarians are often asked to perform autopsies on sudden deaths when a perfectly healthy mature animal with no previous history of illness suddenly turns up dead. This often baffles the producer as well as the veterinarian. Thankfully they are generally sporadic, but a careful autopsy will provide the answer and some possible changes to management.
With many cows now being autopsied for BSE testing I believe we are finding this problem is and was more common than we thought.
In these autopsies, the veterinarian may notice the lungs seem over-inflated and there is some type of an interstitial reaction, but not typical of those seen in common respiratory conditions. Often the animals are in excellent to even too fat a body condition and that prior to death there has been almost no struggling. It would almost appear that the individual cow or bull collapsed or passed on in its sleep.
If a complete autopsy is performed the other consistent finding is abscessation on the liver. There is usually one large abscess involving a good proportion of the liver but in some cases multiple abscesses are present.
By careful dissection one can see a connection between the abscess and the large vessels running through the liver. The very large one is called the vena cava, which is returuing blood to the heart from the body. What happens easily explains the sudden death. The abscess is like a time bomb waiting to go off. As it grows, depending on its location, it can erode into the wall of the blood vessel. If it breaks through, the pus flows into the blood vessel to the heart and is pumped directly to the lungs. This sudden spread plugs all the small vessels in the lung, resulting in respiratory failure and a very sudden death.
I have seen this in old or young cows, yearling bulls and older bulls insured for lots of money.
By sending tissues from the lung into a lab this is fairly easy to confirm histologically (looking at the cells through a microscope).
These abscesses have probably been present since the animal was a young feeder calf and have gradually grown to the point of becoming a problem. The two main causes of liver abscesses are from navel infections in very young calves. As you know, these calves have a history of being treated and more times than not are not retained as breeding animals.
Most other cases of liver abscesses result from mild to severe cases of rumenitis or grain overload. If there is too sudden a change of diet, the rumen becomes inflamed and bacteria seed out into the liver. The result is the start of a liver abscess.
Many of these can be seen in some feedlot animals at slaughter but seldom do they have time to grow large and break into the blood stream as I have described happens in these older animals. They probably do happen but may be missed on an autopsy or the autopsy is never performed on an incidental death.
If one animal has died from this condition there very well could be others in the herd in varying stages of liver abscessation. They would appear healthy and even if we do blood counts looking for infection or checked various liver function parameters they would be normal.
Every time we as veterinarians must try and analyze the feeding program and make sure rumensin (monensin) or another ionophore has been used and the transition from roughage to a grain diet is gradual. We can’t prevent all the cases but it must be explored.
Just as liver scoring is done on feedlot animals, if a group of cull cows are shipped and butchered, or on all deaths, check the liver and if there is a concern show it to your veterinarian. You may be able to formulate a plan to reduce their incidence. If you find many livers with abscesses, this indicates a feeding problem or the lack of ionophores being added. Cattle will not do as well and the incidences of these abscesses rupturing will increase substantially. These are huge losses especially on valuable breeding stock or show animals. The cattle raised on a hotter feed will have a higher incidence, of that there is no doubt.
Make sure and have these sudden deaths autopsied and make sure the liver is checked, as well as the other internal organs such as the kidneys.
Roy Lewis specializes in beef cattle at his practice in Westlock, Alberta.