Is it farther or further?
Old English fola "foal, colt," from Proto-Germanic *fulon (cf. Old Saxon folo, Middle Dutch and Dutch veulen, Old Norse foli, Old Frisian fola, Old High German folo, German Fohlen, Gothic fula), from PIE *pulo- "young of an animal" (cf. Greek polos "foal," Latin pullus "a young animal," Albanian pele "mare"), from root *pau- "few, little" (see few).
"give birth (to a foal)," late 14c., from foal (n.). Related: Foaled; foaling.