i Register
In some senses, bellower is marked as obsolete, colloquial. Watch for register when choosing this word.
noun
One who bellows.
And these [oxen] the wittie-borne (Argicides,) set serious spie vpon: Seuering from all the rest; and setting gone Full fiftie of the violent Bellowers.
1794, Robert Jephson, Roman Portraits, London: G.G. and J. Robinson, lines 558-561, p. 38, Besides, the scent of mischief lur’d along (The scum of towns) a numerous noisy throng; Bellowers, unfit to govern or obey, Who little heed the cause, but love the fray;
A town crier.