Animal erythropoietin modified polypeptides and their uses

A polypeptide of feline erythropoietin (Fepo) comprising an encoded amino acid not naturally linked to a water soluble polymer, wherein: the amino acid corresponding to position 1 of SEQ ID No 2 is replaced with the encoded amino acid not naturally; naturally encoded amino acid is para-acetylphenylalanine; and the water soluble polymer comprising a moiety oxyamino poly (ethylene glycol) having a molecular weight of 20 kD, 30 kD or 40 kD.