Turnip photosensitivity in cows
Turnips can cause photosensitivity which often coincides with periods of Facial Eczema (FE) risk. This may lead to a misdiagnosis and doubts about the FE prevention strategy in use at the time. In NZ more cases of so-called ‘rape scald' are due to summer turnips than any other brassica crop.
The risks are greatest when:
- The crop is fed before maturity
- Excess sulphur or nitrogen fertiliser has been applied
- The crop has been stressed by disease or water restrictions
As for other crop-related health issues, grazing management can be used to minimise the risk. Allow cows to adapt to the crop. For the first 10-14 days, cattle should be ‘filled up' with pasture or supplements before accessing the crop. All cows should go onto the crop together to prevent gorging by a few and time on the crop should be 1-2 hours or less.
After this transition period, standard practice is to allow access after the morning milking. In this way milk taint, caused by feeding the crop close to the afternoon milking, is avoided. This means cows go on hungry and that the early arrivals get a bigger slice of the pie and are at increased risk. If possible, provide alternative feed prior to access and feed only 35% of the diet as turnips for milking cows.