Straw isnt as nutritious as hay so shouldnt put weight on or affect laminitis unless hes eating an awful lot.

if it is summer, feed is the least important (not realy but read on) the grass is richer in summer so your horse could just be enjoying the richer grass.Make sure you give your pony a long-ish lesson,keep your pony entertained and make sure he/she is doing some hard work.Your pony might just need more excercise,Not sure why your pony has like some kind of adiction to hay so i hope this helps.   From Amy and i hope that this helps reply when you can amy.x