How St John’s Wort can cause sunburn in cattle

A weanling with acute photosensitisation showing red nose and swollen face. Picture: Hazell Mullins

The status quo has returned this week. I am back to my beloved cows with a busy week of TB testing in the shadows of Galtee mountains in Mitchelstown. The natural beauty of the area is remarkable. The constant change of county flags is fascinating as I borderhop between farms from Cork to Tipperary to Limerick and Waterford.

I wrote about dangerous plants and trees to both our grazing animals in last week’s article, it is such a vast topic it was impossible to mention them all. However, I did briefly speak about Rag wort and its toxicity to the liver which leads into this week’s topic of Photosensitisation in cattle. St John’s Wort is most commonly associated with the disease in cattle, a plant I failed to mention last week and I just so happened to come across a few mild cases of Photosensitisation during my TB tests this week.