04/05/2026
Well, it's time move on with our lives now the subject of my last post has been dealt with.
As a result, as time allows, we will hopefully be getting back into posting more interesting cases and stories for you to enjoy.
I thought we would kick things off with a case we had over this Autumn.
WARNING – GRAPHIC IMAGE!
Back in early March, we were called to examine a sick, young Kiwicross dairy cow, #482, on a local farm.
The cow had been found to be off her milk and very slow moving.
On examination, she had a fever of 39.8 degrees Celsius, increased respiratory rate and was quite unwell.
We utilise ultrasound examination on most of the sick animals that we look at, so in this case we were able to use it to take a closer look at her lungs. Methylated spirits is what we use directly on the skin to let the ultrasound scanner see past the hair and skin.
Ultrasound revealed pleurisy, with increased lung density and abscesses present.
Severe pneumonia!
#482 was prescribed a long course of strong antibiotics and pain relief to try and get her well again. We left her in the care of the farm, and didn’t hear anything more for a few weeks.
In late April, #482 came to a terrible end. One of the farms staff members had found her distressed when the herd was shifting. She had blood coming from both of her nostrils and her mouth, and she was unable to stand. She died shortly after.
This shocking presentation is called Caudal Vena Cava Syndrome.
Caudal Vena Cava Syndrome is most often the end result of bacterial infection causing rupture of the large blood vessel, the Vena Cava, where it passes through the chest.
This comes about through a long preceding course of events.
It starts when a cow suffers an episode rumen acidosis (grain overload). Bacteria are able to escape out of the gut and into the body. These bacteria usually enter the bloodstream and end up lodging in the liver, where liver abscesses form.
As the abscess grows, it may rupture into the vena cava and form an infected blood clot. Infection the has a direct path to spread back towards heart and lungs.
What we saw initially as pneumonia is likely to have been the result of the spread of infected blood clots throughout the lungs.
We have some images of what the lungs look like from a previous case. The lung tissue is normally airy and light pink, and soft like a sponge. The post mortem pictures show dark red lungs which are filled with fluid and infection, not air.
There is also an image of an abscess which has eaten away at the wall of the Vena Cava, causing it to rupture into the lungs and lead to the cow bleeding out.
Going back to the root cause of this syndrome – Rumen Acidosis.
Rumen acidosis can occur in any animal which has a rumen – think cattle, sheep, goats, deer and alpaca for a starters.
Acidosis occurs when the rumen pH drops below 5.5 due to the accumulation of high amounts of acid. In ruminants, this is usually from eating too much rapidly fermentable carbohydrate and not enough fibre. The drop in pH kills the healthy bacteria which fill the rumen, damages the gut lining the rumen and allows bacteria to translocate through the wall of the gut.
Other outcomes of rumen acidosis include a drop in production, hoof issues such as laminitis, and rumenitis (inflammation of the lining of the Rumen).
Acidosis is possibly one of the most under-appreciated diseases we experience in New Zealand. Where your mind might focus on a clean, green, pasture-based diet, it is easy to forget that many of the supplements we feed our livestock, whether as the main part of the diet in dairy cows (fodder beet, maize, grains, molasses), or as ‘treats’ or to ‘top up’ the diet of our pasture pets (fruit, multifeed nuts, bread), are full of readily fermentable carbohydrates.
It’s not that livestock cannot eat any of these things safely, however, the way we feed them needs to be taken into account.
It is the bacteria in the rumen which break down what an animal eats into the components which the body needs. Different bacteria are needed to process the different components. It takes the rumen bacteria a few weeks to fully adjust to changes in the composition of the diet – so if the diet changes all the time – think for example, if you feed your animals pellets once a week as a treat, or the stock have access to a molasses lick block all of a sudden, or on a dairy farm, if maize is ramped up too quickly, then the rumen bacteria struggle to adapt, and acidosis will occur.
When we change the diet, changes must be made in small increments and over a period of weeks rather than just a few days. The diet should also be stable from day to day, not changing every other day depending on what we feel like feeding. This will look different depending on whether we are feeding a sheep, goat, cow or alpaca.
For 482, as a young cow on a high-input diet, there are a few possibilities for how she developed acidosis, severe pneumonia and caudal vena cava syndrome. It is important that every one of us who is responsible for feeding livestock is aware of Rumen Acidosis and the extent to which it can cause disease in our animals.
