Recently, I was called out to a farm to visit an adult suckler cow with pneumonia.

The farmer was worried about his cow as he said she was having a lot of difficulty breathing and was frothing from the mouth. He also mentioned that she had no increase in temperature, which seemed to make him even more concerned.

Before arriving on the farm, I was considering the most likely agents that could be involved. Lungworm could be an issue at this time of year, but this was not a young cow and surely would have immunity by now. Viral and bacterial components were also high on the list, but the cow surprisingly had no temperature. Still, I thought it best to examine the cow before coming to any conclusions.

On presentation, the cow was showing full signs of pneumonia just as the farmer had described. As I examined the animal further, the farmer mentioned the cattle had been moved onto lush fresh grass just five days earlier. He said he was carrying extra stock this year and that the cows had grazed their previous pasture very bare. It was then that I thought of fog fever.

Fog fever can be described as a nutritionally-induced cause of sudden-onset pneumonia. It can occur about one to 14 days after introducing cattle onto lush, protein-rich grass having come from a much lower protein diet. The rumen is simply unable to adjust to the cow’s new diet. The increased levels of protein (l-tryptophan) in the grass are degraded in the rumen and converted by ruminal bacteria to a toxic product called 3-methylindole. This product travels in the bloodstream to the lungs, where it damages the lining of the air sacs, leading to emphysema and fluid buildup in the lung tissue. This is manifested clinically as signs of pneumonia, which the cow on this farm was now displaying.

There is no specific treatment to reverse this condition, but mild cases may recover spontaneously. From my experience, anti-inflammatories and antibiotics can help but severely affected cattle may die within 24 to 48 hours from the fluid buildup within the lungs.

Preventing access to overly lush grass is advisable. Strip grazing or limited grazing time in high risk areas may help in preventing new cases. Some drugs are also available to create a healthy ruminal environment and prevent ruminal bacteria producing the toxic compound involved.

Luckily, in this case the symptoms were mild and the cow recovered.

But, in a more severe case, we may not have been so lucky and there is little any vet can do to save the animal.

*Mary Louise Coleman works at Mulcair Veterinary Clinic, Newport, Co Tipperary. Mulcair Vets is part of XLVets. XLVets is a group of progressive practices working together to achieve a better future for agriculture and veterinary in Ireland. See www.xlvets.ie for more