The allusion to a butcher’s dog is to a dog that would be expected to be very well fed from scraps. Why that is considered to epitomize fitness isn’t clear, as it might be thought more likely that the dog would be overweight than fit. There is a variant ‘as happy as a butcher’s dog’, which matches the well fed meaning.
Some years ago I published this page saying that the expression first appeared in A Dictionary of Modern Slang, Cant and Vulgar Words, 1859. That was a mistake on my part.
Actually I didn’t just make one mistake, I made two. The citation I had found was to the phrase ‘like a butcher’s dog’, which is a different phrase from ‘as fit as a butcher’s dog’. The second mistake was that ‘like a butcher’s dog’ doesn’t appear in Hotten’s dictionary.
That hasn’t stopped numerous blogs and websites reprinting the Hotten citation – despite that book being online and searchable and not containing either expression. Hum hum.
Sorry about all that – the corrected version is below, please read on…
What I should have said was that ‘as fit as a butcher’s dog’ is a 20th century simile originating in the north of England. Having been little used, especially outside of the UK, it came to prominence following Prime Minister Boris Johnson claim in 2020 that he was ‘as fit as a butcher’s dog’, following his recent weight loss and self-isolation due to a Covid 19 symptoms.
The first example that I know of the expression appears in the English newspaper The Guardian in February 1970. The story is about the theatre director Peter Dews:
“Got married… went back to Bradford to play ‘King Lear’ on me honeymoon and came back to Birmingham fit as a butcher’s dog.”
The expression sounds very like the direct and imaginative Yorkshire style of expression – like ‘If ever tha does owt for nowt, do it for thisen’ [If ever you do something for nothing, do it for yourself] and
‘I could eat t’oven door if it were buttered’. Given that Dews was from Yorkshire and that it didn’t appear again in print for many years, it seems highly likely that’s where as fit as a butcher’s dog originated. It’s a plausible notion that Dews made it up himself, but I have no evidence to support that.
As to ‘like a butcher’s dog’ As I’ve pointed out, that is a separate and unrelated phrase. It first appeared, not in Hotten, but in Francis Grose’s Lexicon Balatronicum: A Dictionary of Buckish Slang, University Wit, and Pickpocket Eloquence, 1811. Grose defined ‘like a butcher’s dog’ this way:
“To be like a butcher’s dog, that is, lie by the beef without touching it; a simile often applicable to married men.”
That ‘something we are close to but cannot have’ meaning is no longer used.
See other ‘as x as y similes‘.