How do i help my damaged palm trees?

i just bought two palm trees and planted them in the front yard. all their leaves have been munched off by cows (i am very angry). just the leafy part has been eaten, not the whole frond. all the stem part is still there. the poor palms look very sad now and i want to know if there is anything i can do to make the leaves grow back or just to make them look nicer?