If someone is in good health, one can say that they are as fit as a flea (or fiddle) in English or as healthy as a billy goat ("terve kuin pukki") in Finnish. What would be a similar idiom in Latin, indicating excellent health? I would prefer an animal comparison if there is one, and in any case something more colorful than optimae valetudinis.
(To make this easier to find, let me repeat the key question in Finnish: Miten sanotaan "terve kuin pukki" latinaksi?)