If your vet knows what they are doing consider doing some blood work on them. If not blood work then I would go with heavy doses of vitamins B and E. Also give some selenium. BOSE is a good choice. Consider some red cell as a booster over about a 5 day period. 1cc per day orally. Depending upon your pen area worming could be needed if they might have picked something up prior to the freeze up. However if this is widespread in your fawns, I would think your pens would have to have had a major issue then to be a parasite issue now. Make sure their nutrition levels are adequate and that a good water source remains available. Snow cover is not adequate especially for animals already lacking in nutritional health. Good luck!