My horse Crystal (quarter horse) is 20 years old. This winter really seems to be tough on her; she's not skinny but she's thinner than I want her to be and she's not gaining weight! At the beginning of winter I was feeding her hay and oats at the amount she has every winter, but when I realized she was losing weight I switched her to a round bale so she could constantly be eating. This seemed to do nothing for her, but has given my other horse a few extra pounds. I thought that maybe it was worms, so I dewormed her, but that didn't help either. I don't know what to do?!?! Suggestions?