I've fed flaxseed (linseed) mashes for over 30 years but never raw. As the link on Reble's reply shows, it is toxic! It contains an enzyme called cyanogenic glycoside which produces cyanide on contact with air. Boiling renders this harmless. I've always soaked it over night then boiled for an hour. Be careful tho, it turns to gloop and boils over very quickly! Just in case you do... the easiest way to clear it up off the stove and floor is with a syringe (minus the needle). High in healthy oils it's a good laxative and fed regularly, produces wonderful shiny coats. It's also used to here to darken coats, especially chesnuts, who turn deep coppery red when fed regularly. I use a teacup of seed to about 2 pints of water to produce a slimy "tea" that can be added to their feed. NB These are the proportions I use for big horses. It also makes a great old fashioned warm mash when mixed with what bran (for cold, tired or sick horses). Wheat bran shouldn't be fed regularly to youngstock tho, due to it's low calcium high phosperous ratios.
Kate