This winter we have been seeing disease in cows which appears to be related to grazing swede crops. Liver disease seems to be occurring with symptoms ranging from illthrift, rapid weight loss, photosensitivity and eventually death.
When grazing any crop problems can arise, especially when transitioning stock or moving from one crop to another eg the amount of crop allocated , to what and how much supplementary feed given.
Though not fully understood, the cause of the symptoms we are seeing , may be related to glucosinolates in the swedes. Due to a generally milder winter in parts of Southland and less frosts earlier on, there is substantially more leaf growth in the swedes and the bulbs appear to be unpalatable. Stock, if given the chance, will consume more of the leaf (where glucosinolate concentration is highest) than bulb and so this becomes a risk factor.
To date we have been called to investigate issues in dairy cows, however there is anecdotal reporting of illthrift in sheep and beef animals grazing swedes as well.
Many of these crops are now starting to flower which potentially may increase the concentration of these glucosinolates in both the leaf and flower so it is advised to remove stock from these crops.
We are part of a multidisciplinary group that is continuing to investigate this issue further. If you are having any issues with stock on swedes, or alternatively are having no problems but are not sure what to do with grazing your crop, then please contact us at the clinic to discuss your options.