I personally believe that most grains and sweet feeds are completely unnecessary. 90% of horses do just fine on a diet of nothing but forage feeds (hays). The only horses that could possibly benefit at all from any kind of sweet feed are the heavily worked performance horses who are ridden hard every single day, sometimes for several hours. IMHO, no horse that is less than moderately worked needs any kind of specialized feed other than perhaps a weight builder for those hard keepers. No excess sugars or carbs. Sweet feed carries more risks than benefits, between founder/laminitis, EPSM, or insulin resistance it is just too big of a risk. I prefer to feed a diet of only hays; grass or alfalfa with a free choice trace mineral block and all my horses are happy and healthy. We don't have issues with diet related illnesses or diseases, never had a case of founder and haven't even had a bout of colic since we stopped feeding sweet feed about 16 years ago. If a horse does need a more balanced or specialized diet, then there are much safer options out there like complete feeds that are properly balanced for the activity level, age, and necessity of the horse.
If it is just given as a treat, then there are safer and cheaper options. You could get a bag of alfalfa cubes or pellets and feed a handful of those as a daily treat.