By Lisa Whitfield
It’s the phone call no one wants to receive any day of the week, let alone on Sunday morning over a long weekend. One of the top animals from the R1 replacement heifer mob had died unexpectedly, after a short illness.
Diarrhoea, mild respiratory signs and depression were the main clinical signs observed over a few days. Two heifers were affected, but they had been on treatment and had shown improvement.
It would have been easy to just leave it at that – a phone call or two to arrange for disposal of the carcase, and the weekend activities could have carried on uninterrupted. But why did she die?
A post mortem on a cow is not what I would describe as a quick, easy or clean job, and the logistics of dealing with a 250kg+ carcase add to the problems
Arriving back home mid-afternoon with the carcase in tow on the trailer, it was going to be a rush to get the rest of the jobs on the farm done before dark. There was the option of storing the carcase in a large chiller until the vets opened again on Tuesday – this was tempting as it meant finishing the day before dark.
It would have been easy to take this option, except that the longer the delay in getting a post-mortem performed, the lower the chance of finding out what had caused her death – and we knew it was important to find out why she had died. The decision was made to do the post-mortem that day.
The vet couldn’t be there until 4pm, so there was just enough time to shift the herd off the winter crop and move the break fences for the next morning.
The post-mortem took about two hours to perform. It was a good decision to get it done there and then – there were limited obvious gross changes so taking samples was necessary, and early decomposition was already setting in. Once decomposition takes hold, it becomes very difficult for the lab to analyse tissue samples and find the cause of death.
Gross lesions were found in her gut and she had inflammation around her bladder. A multitude of samples were collected and preserved in formalin – liver, kidney, spleen, lung, heart, gut, bladder – all would be submitted to the pathology lab to be examined under a microscope. All that could be done now is wait. By the end of the week, the results were in – the kidneys and gut had lesions which pointed to Bovine Adenovirus 10 as the cause of death – and subsequent testing using PCR confirmed the diagnosis. No one could have predicted this result – in fact we had never even heard of it as a cause of disease in New Zealand before.
It turns out Bovine Adenovirus 10 is a sporadic cause of disease and death in R1 heifers over autumn, winter and into spring, and there are a few reports of outbreaks around the country. While the virus is widespread in the cattle population it rarely causes serious disease or large outbreaks. Stressors such as bad weather, transport, parasitism or other diseases can trigger outbreaks. Clinical signs include diarrhoea, depression, respiratory signs and often severely affected animals will die. Getting an answer could be considered reward for effort if you want to look at the whole thing in a positive light. We now knew what we were dealing with, and while there wasn’t much we could do about it, the chances of more losses seemed likely to be low. No one was to blame either – it was just bad luck. A post-mortem is an under-utilised tool in NZ farming. There is value in knowledge, and getting answers can allow you to prepare and/or prevent ongoing stock losses.
- Lisa Whitfield is a Manawatu production animal veterinarian.
