High Nitrate Oats

[NZDan]

I've grown my first crop of winter forage oats, just DD into sprayed of rank Browntop in Autumn (April 10th) with 180kg of DAP. with the idea of grazing the ewes on it for the final 6 weeks before lambing. Tested the nitrate levels on Saturday the day before the ewes were supposed to go on. Nitrate levels over 500!!!! Any one got any ideas for getting it down to a safe level, or will it get lower as the plants mature into the spring.
We've had a really warm dry winter here, I'm struggling to get electric fence stakes in the ground!!!