Five years ago I really worked on my first herd health investigation start to finish. It was a herd of coughing cows or more accurately a herd with a respiratory disease problem. Cutting my teeth in that case was a steep learning curve. Since then I’ve investigated many herds of coughing cows and have got better at working up these sometimes complex cases.
So what causes a cow to cough?
Firstly anything that irritates the nasal passages, trachea (windpipe) and bronchi can cause coughing. This in adult cows often is termed as upper respiratory disease and is often associated with viral infections like IBR RSV Pi3 to name a few.
This can often lead to deeper lung infections also.
Then you can get coughing from deeper infections of lung parenchyma (the lungs themselves). This is a much deeper infection often caused in adult cows by bacterial pathogens and or lungworm. A much deeper cough and often when bacteria are involved a more aggressive severe condition which can be slower to resolve to treatment.
What level of coughing is a problem?
Good question, of course cows at herd level can give an odd cough. When coughing is persistent and frequent especially when being moved or at housing and milking. More importantly if there is other evidence such as sick cows, milk drop etc.
What other symptoms raise alarms?
If you are noticing increased incidences of sick cows requiring treatment for pneumonia.
If herd milk production is dropping or other factors such as fertility are being affected.
If cows have nasal discharges or temperatures.
Can time of year or type of cough tell us anything?
To make assumptions is dangerous.
The type of cough and time of year can give us indications of what might be happening. Focusing on lungworm, the cough tends to often be very deep and when no viral/bacterial infections present with out major nasal discharges.
Of course timing can give us indications as well. Lungworm is predominantly a pasture problem from June onwards. When we see cows coughing at housing or around calving I'm always more suspicious of viral infections.
However that’s the end of the assumptions as lungworm seems lately to have thrown the rule book away.
Where do we start when investigating the problem?
When history and clinical signs are dealt with, this will often direct us down certain diagnostic routes.
In summer months with coughing cows we can take faecal samples to check for lungworm, bloods, nasal swabs or more recently more vets are opting to do highly valuable lungwashes for more accurate diagnosis.
At calving time we tend to look more at bloods, nasal swabs and looking at underlying nutritional stressors.
Your own vet is best placed to figure out where to start.
Should cows not have immunity to lungworm
Yes traditionally this was the accepted principal. However, nowadays we are unfortunately seeing more adult dairy cows having issues with lungworm.
Two main reasons; young stock are being so well dosed their ability to create natural immunity to lungworm is impaired – the ‘belts and braces’ approach to worming for the want of a better term. Meaning when they enter the milking herd they are more susceptible. Ideally we want younger animals to develop immunity over time to low levels of lungworm.
We also have seen reinfection syndrome, this can be complicated. What happens with lungworm is there are two levels of immunity at the gut where the parasite enters the body and at the lungs. The immunity in the lungs is lifelong while the gut immunity wears off after a while.
With reinfection syndrome we have larvae getting to the lungs because of short gut immunity and not developing into adults which causes problems. These can be difficult to diagnose because they don't fully develop into adults (because of life long immunity at lung level) meaning no eggs are produced to pick up on faeces testing.
These cases often need lung washes to diagnose.
Any problems with dosing frequently?
This can be costly and also may lead to resistance in the future. It is one way to control lungworm in adult cows but I feel an unsustainable one. This is where I have considered and used vaccination where lungworm was a severe issue on farms.
What role does grazing and weather play?
Firstly mild wet summers are ideal for lungworm. Problem is these conditions, if favourable can mean lungworm levels in pasture can spike quickly. Add in a tight grazing system (4cm post grazing height) and heavy stocking densities and we certainly have big contributing factors in some farms.
It might be two problems one cough?
Yes on many occasions I’ve seen this.
At calving time or early spring it can often be nutritional stress with viral infections for example. Another example during the grazing season is lungworm and viral infection, both contributing to the problem. Where cows start with a lungworm problem, over time secondary viral and bacterial infections can also affect cows.
Is this a new phenomenon?
It's probably not all that new but we have seen a notable increase over the last 8-10 years. However, there is no doubt that worming strategies in youngstock, weather conditions and increased intensification have speeded up the process. If you are treating your dairy herd on multiple occasions during the grazing season with Eprinomectin ask yourself the question do I have an issue. Use this sign as a trigger to talk to your vet.
Did this help?
I hope I have highlighted that coughing cows can be complex and requires input from your veterinary practitioner.
We cannot make presumptions and it will cost us money via production losses and treatment costs.
My advice is make a diagnosis to make a difference to your herd!