I feel your pain OP.... Thanks to all this lovely forever changing weather we are getting in NZ the sugars in the grass are going crazy and I have two tbs on dairy grass!
Personally I would try feeding Tox Defy for a few weeks and see if that makes a difference, however it does work better in conjunction with Alleviate (I use Alleviate C because of the extra calcium in it) - this is after making sure it's not a pain problem though!
If that doesn't work then I would go for blood tests for the likes of Selenium as that can be low in New Zealand pastures, but we can't supplement that one unless it has been proven to be low in the system because an overdose can exhibit similar symptoms as a deficiency can
R.I.P ~ Bubbles - 25yo tb mare - 13.04.2011 ~ 8:30am ~ passed away naturally and peacefully in my arms