Tonight's Vet Finals session is an approach to the adult cow with diarrhoea… here goes!
First up we need to have a think about differentials for diarrhoea in an adult dairy cow. Although there are a lot, there was a lot of agreement as to the most likely causes.
There was a little confusion with some people including PGE and coccidiosis on their differential lists, but this was quickly cleared up.
Now that we have our four main differentials sorted, we need to have a little think about the questions we might want to include if we're taking a good history.
So we've got an individual cow in poor body condition, milking badly, and diarrhoea. Onto some descriptions of the diarrhoea… Liz regretted watching the conversation at this point!
And so (on that note) onto the clinical exam…
So we've got an individual cow with a low BCS but who is otherwise fairly normal. What does that do for our differential list?
We were all coming up with pretty much the right answer… yay!
Well done everybody! Lets see if we can differentiate between fluke and Johnes now…
First we have a little think about the time of year and grazing likely to produce a chronic fluke case like this one….
And now onto testing for Johnes… lots of answers were mentioned here. To summarise, There are 3 main types of testing:
1. Faecal culture- takes a long time (2 months). Culture can also be done on environmental samples.
2. Faecal PCR – Result in less than a week. Similar sensitivity to culture. Very specific.
3. Antibody titres (ELISA)- can be done on blood or milk. Very quick and cheap, usually very specific (see clarification in a moment) but has a similar sensitivity to the other two (40-45%). To improve the specificity we often test the same animals repeatedly.
A quick diversion to discuss sensitivity and specificity, with a helpful tip from John….
Most people seemed to think that blood antibody testing would be the quickest and cheapest option in a cow with clinical signs, although some people were also keen for faecal PCR. Don't worry- both are correct answers!
Then John through in a curveball that really got us all thinking….if we get a positive on a blood ELISA, what is our PPV?
That was a mean question… although the specificity is high for the test, we don't know what the PPV is because we don't know the prevalence in the herd.
Another curveball from John…
Of course, Michelle had a good point- it's important to remember the clinical picture of the cow right in front of you as well as what the test results are trying to tell you!
So, we've hit 9pm and we're onto a quick treatment… although in this case it's not so much treatment as….culling. And then some prevention.
But remember that this is a 'tip of the iceberg' case and the management really hinges on prevention. Calves are the most at risk of catching Johnes so this is where preventative efforts are focused. Also important is the identification of cows likely to be shedding the virus and removal from the rest of the herd. Risk assessments are a common tool used to target preventative efforts.
Just before we leave Daisy asks a very good question….
And that was that! Thank you again to John for running the case and also for staying late, as it was past 9.20 when he finally logged off and left us to it!
There are more resources here: actionjohnesuk.org/ and http://inpractice.bmj.com/content/31/4/150.abstract?sid=3842c7c2-1c79-4a5c-9baf-22920124fe1d …
Next session is on the Bleeding Dog and is being run by Nick Bexfield on 12.4.16 at 8pm….see you there!