Farm Ireland

Friday 23 March 2018

How to boost cows' immunity to disease

A long-term plan is essential for dealing with respiratory conditions in dairy herds

The causes of coughing cow can be complicated
The causes of coughing cow can be complicated

Over the last two months, I've been dealing with a number of herd problems with respiratory disease in cows at pasture. There is a lot of confusion about the causes of this problem and it can be very frustrating for farmers as it can have a significant impact on production.

Unfortunately, there is rarely a simple solution because often, when this type of herd problem occurs, there can be several things involved or contributing.

I'm not talking here about individual coughing or sick cows, but herd problems usually with large numbers of cows affected.

These cases, in my experience, are usually caused by infectious agents such as viruses or parasites.

What can complicate the situation is sometimes there will be a combination of things affecting the herd at pasture. We also need to find out if there is any reason for the herd immunity to be dropping. Anything that affects immunity will leave cows more prone to shedding and becoming infected, particularly with viruses.

The main causes of coughing I have diagnosed in the last two months have been viruses and lungworms. The viruses I have found have been RSV, PI3, IBR and coronavirus. For some reason, the first disease everyone talks about when talking pneumonia in cattle at the moment is IBR.

My experience is, yes, it does cause the clinical signs of milk drop and coughing, but it is not the only agent I have isolated. Of course, it is a hugely significant worldwide disease and many countries are now trying to eradicate it.

However, we need to move away from blaming it exclusively for the coughing cow. Instead, we should make an attempt to definitively find the cause, or causes, of the coughing.

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There is also no doubt that lungworm is affecting some of these herds with coughing cows. Lungworm requires warm and wet conditions for larvae to develop at pasture. In my experience, the last two months have been perfect for this.

On its own, it can be straightforward, with a treatment usually resolving the problem in a short number of weeks after a dose. The initial symptoms tend to be coughing at pasture getting much worse when cows are moved. In adult cows, we now deal a lot with reinfection syndrome with lungworm.

This can be difficult to diagnose as faecal samples will often be negative and the only way to diagnose this can be by lung washes, which are difficult to perform.

However, more commonly I'm seeing that the initial lungworm infection will allow secondary viral respiratory problems to spread through the herd. This will complicate recovery and response to treatments. So what starts with lungworm issues subsequently becomes a viral infection as well.

With a number of complex interactions taking place, it is a good idea to start by building the clinical picture and using diagnostics to draw up a short and long-term plan.

One very significant thing that can contribute to viral disease spread can be negative energy. This can occur at pasture when cows are producing milk off grass and are off meal. The cows aren't getting enough energy from grass alone for the milk they are producing. This can be down to poor covers, poor intakes, acidosis, etc.

If prolonged, this nutritional stress or negative energy can lead to virus shedding, which, in turn, can end up being an entire herd problem.

It is important to remember also most of the viruses we described earlier are circulating in the herds and usually require a trigger like lungworm or stress to start shedding and spreading.

The question I'm often asked is where did the virus come from? In closed herds, the viruses can be lying dormant and usually require some stress to start shedding. It is not unusual that herds that buy in stock are more prone to viral infections simply because this animal movement allows the spread of viruses much more rapidly.

You must also remember a bought-in animal will usually have been quiet stressed due to transport and getting acquainted with the new herd.

It is during this time of stress they are most likely to spread whatever viruses they may have. This is why we recommend quarantining new arrivals on farm.

So owing to the potential complexity of the condition, I try to work through the process methodically and build up a clinical picture. My seven-step plan isn't bomb-proof but I find it more useful in drawing up long-term control plans.

It is worth remembering that if coughing or respiratory disease has been going on for several weeks, then it can take time for the problem to resolve.

In some instances, we have put cows on once-a-day (OAD) milking for two to three weeks to take the pressure off cows and allow them to recover.

This type of approach leads to more strategic control planning that shows the long-term value in diagnostic testing.

Tommy Heffernan is a vet at the Avondale Veterinary Clinic, Rathdrum, Co Wicklow.

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