With a ration balancer, if they lose weight, you can just add rice bran/alfalfa hay pellets/beet pulp to help them out a bit.
You don't want to up the RB like you would when feeding grain, but adding rice bran/beet pulp/hay pellets isn't bad at all.
That's actually what I do for Lacey - she's basically overweight all summer but gets ribby by late Decemeber/January. So during the summer I feed her the RB by itself, then in the winter I add rice bran/beet pulp/alfalfa pellets as needed.
Right now she's getting her RB and a mix of rice bran (1/4lb)+beet pulp (1/2lb) and that's keeping weight on her nicely.
I had been using alfalfa pellets in place of the beet pulp but the last time I went to the feed store, they were out. Sooo I ended up with beet pulp. haha
I had never tried rice bran before this winter but decided to try it after she started getting really picky about finishing her dinner. Apparently rice bran tastes great and since adding it, there have been no problems with her finishing up her meal.
Fabio - 13 year old Arabian/Lipizzaner gelding
Hazel - 14 year old Angora goat
Atticus - 4 year old LaMancha/Alpine cross goat
Rest peacefully, Lacey.