Originally Posted by OliviaMyee
OMG I just found pure organic Magnesium Oxide for sale online its 227g its 8.00$ and horses only need 31mg of Magnesium Oxide per day so this combined with the trace mineral supplement seaweed stuff that contains the nescacary vitamins and minerals will give me a great diet.
When feeding Magnesium Oxide, horses need 31 mg per kilogram of body weight
, or about 15.5 g for a 500 kg (~1100 lb) horse. That 227g bottle will only last 2 weeks at that rate. Read more
I'd really recommend against supplementing individual minerals unless you know specifically what your horse needs- not just doing research online, but also having your hay and/or pasture tested, calculating what they're getting from any other feed/supplements they might be getting, weighing the food each time you feed, etc.
FeedXL.com does a lot of the calculations for you and is a great site for building a diet, but of course you'll get most accurate results if your hay/grass is tested.