I use the blender and grind enough for 4 horses for 1 day all at once. I once tried to feed the whole flax and it did not make the difference in their coats I was used to seeing. That was proof enough that it does need to be ground for them to utilize it as well.
The seeds are small and hard and unless the horse actually chews it good enough to break the shell, it will pass through completely undigested. I figured out that I was wasting alot more than my horse was getting chewed by not grinding it and im a waste not want not kinda gal.
If you fill a regular blender about halfway to 2/3 full and just turn it on and don't shake it till it stops moving up the sides, it will grind it just like a coffee grinder but do a whole lot more all at once.
Fresh ground is vastly superior and does not waste. I bet half of what I was feeding or more was passing through undigested and its worth my time to take 3o0 seconds a day to grind it up.
Boiling it is now unnecessary but probably done before the days where it was common to have blenders and coffee grinders since it does spoil when ground and people in those days did not like to waste. Many things pass on from generation to generation not taking in to account the change in the times and knowledge.
So long story short, IMO and IME, grind it daily for the best utilization, but no need to boil or add water.