If you need less than 25 lbs, www.hoeggergoatsupply sells it also in smaller quantities; it does last a long time, but you can use it for all your animals and in your garden, too.
We tried kelp meal on our chickens for the first time this winter. It was amazing how much weight they gained (except Dazzle, who never eats til all the hens are full...) They seem to be in better condition overall through the winter than in previous years, also.