This time of year Facial Eczema is on everyone’s mind. However, you may be seeing signs of photosensitivity (“sunburn” or “scald”) despite the spore counts still being low. At this time of year, brassica summer crops (forage rape, turnip) are also being fed, and these can result in photosensitivity occurring at a similar time to Facial Eczema.
A cow suffering from photosensitivity will be agitated and restless in the early stages. She may seek shade. Red and inflamed teats are often noticed first, then white areas of skin swell, feel raised and may peel.
Compounds in the plants are broken down in the liver and may cause liver damage. The damaged liver is then unable to process photoreactive components from plants, leading to their build-up in the blood. When the cow is exposed to sunlight, a chemical reaction happens between the compounds and sunlight and the skin burns. Liver damage isn’t always permanent, unlike facial eczema.
Photosensitivity is more likely to occur with quick transition onto crop, high intake (especially of just the leaf), high soil sulphur, and grazing an immature crop. The slow transition over at least a week or two allows the animal to get used to a change in diet; accurate crop yield measurements will help with this. Try giving a grass break first so they don’t gorge. Ensure all animals have equal access - move them onto crop together rather than feeding straight after milking and give a long face to the break.
Affected animals need to be removed off crop and given other feed, as well as offered complete shade. Decrease milking to once-a-day or dry off, especially when teats are severely affected. Sunburn is painful - anti-inflammatories are helpful. Anti-histamines can make the cow feel more comfortable. Zinc is unlikely to prevent brassica associated photosensitivity (unlike Facial Eczema). Usually, the cow responds within a few days. Severe clinically unwell cases will need to be seen by a veterinarian and their welfare considered.
Sources: NZ DairyExporter, DairyNZ