The last couple of years have seen several additional gauges be added to the HUD: boat durability, Abigail's health, weremeters, inspiration. So why not just go ahead and add a similar gauge for the health of the Beefalo you are riding. I've always found it rather peculiar that players are expected to just... "guess" the health of the Beefalo they are riding into battle.
The lack of a health bar is also an issue when trying to heal your beefalo, so maybe the meter could be visible for bonded beefalo as well?