I would say that 8 oz. is definitely not enough. My horse is much larger, but just to keep weight on him, he was fed 3/4 of a small bucket twice a day of pellets. (I think Southern States.) I'd say it is about a gallon sized bucket. He also got two large flakes of grass hay twice a day as well. He does not get as much now because he's on pasture grass and not being used in lessons anymore, but that's what he was getting before going to pasture. He's also 16.2 hands and a thoroughbred. He was also being used a couple of times a week in lessons. Hope that helps a little. I do know that they added hay cubes to their pellets as well to help with extra energy. They might help with weight gain too.
Do you think I should double her grain. This is the grain they are feeding in the 8 oz plus I also am feeding her a supplement (Horse Guard I think it is called):
Dixie Grain by Union Mills
Crude Protein, not less than..... 11%
Crude Fat, not less than..... 2.5%
Crude Fiber, not more than..... 13%
Calcium, Minimum %..... .35%
Calcium, Maximum %..... .6%
Phosphorous, Minimum%..... .35%
Copper, Minimum ppm..... 22
Selenium, Minimum ppm..... .4
Zinc, Minimum ppm..... 60
Vitamin A, IU/LB..... 875
grain products, forage products, plant protein products, processed grain by-products, cane molasses, salt, dicalcium phosphate, potassium chloride, vitamin A acetate, vitamin D supplement, vitamin E supplement, vitamin B-12 supplement, menadione dimethylpyrimidinol bisulfite, riboflavin supplement, niacin supplement, D-calcium pantothenate, choline chloride, folic acid supplement, biotin supplement, pyridoxine hydrochloride, thiamin mononitrate, zinc sulfate, magnesium oxide, magnesium oxide, ferrous sulfate, zinc sulfate, copper sulfate, sodium selenite, potassium iodine & cobalt carbonate
Is there something I should be feeding in addition to this or instead of this?