Green’s Dictionary of Slang

brewer’s horse n.

also brewer’s dog
[i.e. one who has fig. been ‘bitten by the brewer’s horse/dog’]

a drunkard; a state of drunkeness.

[UK]Shakespeare Henry IV Pt 1 III iii: I am brewer’s horse [...] Company, villainous company hath been the spoil of me.
[UK]Mercurius Fumigosus 21 18–25 Oct. 181: A sad Musician being lately bitt by a Brewers Dogge [...] found his Head heavier than his whole Body, and so pitched quite over.
[UK] ‘The Good Fellows Song’ in Ebsworth Westminster Drolleries (1875) 108: As we went wandring all the night, The Brewers Dog our brains did bite.
[UK]London Standard 22 Feb. 3/5: How many of you have been bitten by the brewer’s dog like myself?