From feedipedia...
Fresh flax forage: flax crops delayed by weather and damaged by frost can result in incomplete seed development, and in some cases, regrowth, including flowering, may have occurred on the green plant. However, while fresh flax forage is nutritious, it may contain toxic amounts of hydrogen cyanide (HCN) and nitrates, and farmers should exercise caution before feeding it to livestock (see
Potential constraints on the "Nutritional aspects" tab) (
Government of Saskatchewan, 2008b).
If I were to use it I would have it as a part of forage variety, not a staple. Darn! I was excited by the idea, I plan to grow some flax in order to experiment with extracting the fibers. Having the seeds would be nice too, but I didn't plan on growing that much.