This is a confusing saying in Cnósach Focal ó Bhaile Bhúirne. Does it just mean "it's the worst thing possible to leave herds of cows out on the hill", and so it is better to burn your calves with your back to the fire than that?

Is fearr gorradh cúl cos ná na táinte ar cnoc. = It's better to warm back of legs than (to have) herds on a hill.
Having warm feet (i.e. a little comfort) is better than all wealth (i.e. is of great value).

Perhaps a bit similar:
Ní táinte go sláinte.

Thank you, Lars, that makes more sense now.