there isn't much weight different before and after grinding, but the volume may be different.
Recommendations for Omega 3 benefit is 2oz by weight for 1000# horses, so a 250# mini would get 1/2 ounce (I think that's 2 tablespoons of ground by volume). I have larger minis, so most get 1 ounce (fills a 60cc scoop), a few get 2 oz (1/2 cup), and some get 1/2 ounce.