Hi. We own a draft also. A 9 yr. Old Belgian mare.
THis is just my opinion, and others may disagree but I FIRMLY believe that ANY draft not in heavy work should not be given grain!
Two of the main reasons is that drafts are susceptible to metabolic disorders, like IR (a horsey equivalent of Diabetes), especially from high sugars/NSCs....these disorders are serious and sometimes life threatening.
The second reason is weight....drafts are notoriously easy keepers and can get fat off of air...lol. Seriously overweight drafts are at high risk for founder. Founder is a serious problem in ANY horse, but My farrier told us that founder in drafts is a bit more serious than in a standard size horse in that they don't recover as well (or not at all) due to the weight isssues. They carry alot more weight on those hooves, so when they founder, it's not good.
Because our hay's nutritional value changes from shipment to shipment, dealer to dealer and even cutting to cutting...we have our draft on a supplement from SmartPak for easy keeper horses on grass only. That way if we get a batch of poor quality nutrient value hay, she is getting the vitamins she needs.
We also have her on a hoof supplement, Platform Hoof, and have been using it for two years. It has worked wonders for her...not only are her hooves PERFECT, she grows alot of it.....and her coat is so shiny our vet was awestruck by it.....I won't even go into how her tail is so thick and long I have to cut it every single month because it grows so fast she keeps stepping on it and ripping out hunks.
Whether you decide to supplement or not, PLEASE take your draft off the grain....the risks are too great.
And congratulations on being a draft owner, they are such fantastic and powerful horses...you just HAVE to love them!