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Vets in the two RVLs reported that fog fever, which is also called aftergrass pneumonia, killed a three-year-old suckler cow in Sligo and a six-year-old cow in Kilkenny.
The three-year-old suckler cow developed acute respiratory distress, including mouth breathing with her tongue extended, one week after being moved to aftergrass.
In her post-mortem examination, the vets found that the cow’s lungs were heavy with oedema (fluid build-up) and contained diffuse interstitial emphysema, which would cause shortness of breath.
Her lungs had damaged alveoli, that had extended to form large air spaces.
Similarly, a six-year-old cow was examined by vets at Kilkenny RVL, with a history of acute onset respiratory distress. She had similar lung problems as the first cow.
Her lungs had damaged alveoli, that had extended to form large air spaces.
Vets found that both cows had subacute severe pneumonia.
Neither of the cows had bacteria, respiratory viruses or lungworm larvae in their lungs.
Fog fever
Writing in the RVL monthly report, the vets noted that aftergrass pneumonia, or fog fever, typically occurs within 10 days of moving suckler cows to lush pasture in the autumn.
Although many animals within the group may be affected, severe respiratory signs are usually only seen in a few animals.
Large amounts of the amino acid L-Tryptophan found in lush aftergrass is converted in the rumen to a substance called 3-methylindole (3-MI) at a very high rate.
This is absorbed and circulated through the animals’ body and is toxic to cells lining the inside of the lungs.
Vet’s corner: Fog fever in cattle
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