Acidosis Can Kill Cattle Suddenly
At the final year oral exam, a veterinary student with a “hit-and-miss” academic record was asked how many TB bacteria it took to cause tuberculosis in an animal.
Thinking on his feet, he replied “one in the wrong place”.
This catch-all answer has more than a grain of truth in it.
What can be harmless in one situation can be lethal in another.
For instance, the smallest tumour in the brain has much more serious signs and consequences compared to a similar-sized tumour on the hand, such as a wart.
A case of sudden death in a cow, the other day, provided us with another example of the importance of location when it comes to disease signs and outcomes.
We are all familiar with abscesses, the name conjures up an image of fluid-filled swellings that may or may not need to be lanced.
Of course, the animal’s immune system never meant for those swellings to be drained.
Cattle in particular are very adept at walling of infections within fibrous abscesses, in an effort to stop invading bacteria from spreading further in the body.
Many of these abscesses are found in “normal healthy cattle” at routine slaughter, or as incidental findings when autopsies are carried out for other reasons.
Bacteria are always trying to gain entry into animals, and the immune system has to remain on 24/7 alert to keep such invasions at bay.
Amongst the many entry ports are navel infection, cuts/wounds in the mouth or skin, and of course, the stomachs and intestine which are laden with bacteria.
Where bacterial invasion is successful, the best the immune system may be able to do is slow down the invader by “imprisoning” it in abscesses.
Even when all the bacteria in the abscess are dead, leakage of the pus will cause more damage to the organ containing it, and so can cause clinical illness.
Such was the situation in our case of sudden death in a cow.
At autopsy, a large amount of blood was found in the lung, which was the immediate cause of death.
The haemorrhage was due to an abscess in the lung, which damaged a nearby artery.
However, that was only one of many small and medium sized abscesses scattered throughout the lungs, and equally numerous ones in the liver.
This was a classical case of one of the effects of nutritional acidosis that often remains unnoticed.
It is associated with changes in diet, especially diets with a lot of cereal.
This causes the rumen to produce a lot of acid, which damages its lining.
Bacteria seize the opportunity, and are carried by the blood to the liver.
Here the cow’s body walls them off in abscesses, if it can’t clear them out fully.
If bad enough, the animal will show clinical acidosis with diarrhoea, dehydration, and even collapse.
However, most animals may only get an inexplicable fever (often treated with antibiotics as a “chill”), or only have even milder signs like losing cuds (quidding).
The sub-clinical version has become known as sub-acute ruminal acidosis (SARA), and causes serious financial loss if it affects a lot of animals in the herd.
As the winter approaches, and cattle will have to change from grass to silage and grain diets, it makes sense to review now how we might prevent SARA, as part of the farm health plan for all age groups and farming systems.
While some countries use in-feed antibiotics to control liver abscesses, our emphasis has to be on prevention.
While the lung haemorrhage is dramatic and an obvious loss, the real losses are seen in animals that appear normal, but are taking longer to make the weight, or fail to make their expected yield, because we gave one bacterium the chance to get into the wrong place.
Bill Cashman MVB MRCVS MVM, Cashman & O’ Driscoll, Glanmire, member practice of Prime Health Vets
(Source – Irish Examiner – Bill Cashman – 27/10/2016)
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