Green’s Dictionary of Slang

the runt of the litter; the favourite or smallest pig in the litter.

a.?1425		MS Hunterian in Middle Eng. Dict. Pigge [...] Renners aboute fro house to hous as antonie pigges & fro towne to towne..seme þat þei kunne hele of alle maner sekenesse of þe y?en.
1480		Chronicles Eng. (Caxton) ccxliv: And there come to hem an Anthony pigge and folowed the hoost alle that way till they come to a grete water.
1533		J. Heywood A Merry Play in Farmer (1905) 67: But she will go gadding very much / Like an Antony pig with an old witch.
1659		J. Gauden Tears, Sighs, etc. of the Church of England Bk IV 595: Yea some are such Cossets and Tantanies, that they congratulate their Oppressors, and flatter their Destroyers.
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.
1811		Lex. Balatronicum.
1834		‘Jack Downing’ Andrew Jackson 39: [They would] follow arter him jist like a tantoney pig or whipt spaniel.
1846		Swell’s Night Guide 109/2: Anthony, or Tantony Pig, the favourite or small pig, of a litter; to follow like a tantony pig, that is, St. Anthony’s pig to follow at the heels.
1867		Standard 24 May 3/5: ‘What is an Anthony?’ ‘The littlest pig, your honour. The little pig is always “Anthony”’ .
1873		Derbyshire Times 26 July 5/2: Anthony Pig. The ruckling of the litter.