I have 3 own root roses which suffered severe damage from rabbits during the winter which I pruned off. They were not very large to begin with. They were beginning to show new growth so that was encouraging but we were zapped by a 20'F frost about 2 weeks ago and the new growth is now dead. There is a little green cane remaining below where the new growth was (less than 3 inches) What, if anything, can I do to save and hopefully get some new growth started. These were all hardy roses and not finicky tea roses. I haven't fertilized yet.

I would not fertilize them just give them plenty of time to recover. Not sure which planting zone you live in, but own root roses are hardy here in zone 4. I have some own root roses that have been here for years, some winters the rabbits damage them, after they start showing new growth I prune the damaged canes back. Be patient and when the roses have plenty of new growth you could fertilize them lightly with fish emulsion which roses love.

Welcome to NGA!