The present disclosure provides recombinantly manufactured ultra-long acting insulin-Fc fusion proteins for use in treating canine and feline diabetes. The insulin-Fc fusion proteins comprise an insulin polypeptide linked via a peptide linker to an Fc-fragment of canine or feline origin. Based on the results obtained, creating a treatment that is amenable to low cost manufacturing, exhibits sufficient in vivo bioactivity, displays extended duration of bioactivity, does not induce anti-drug antibodies, and substantially retains is potency over multiple administrations, requires a non-obvious combination of insulin polypeptide, peptide linkers, and species-specific Fc fragment, in addition to selective mutations on one or more of these components. Exemplary ultra-long acting insulin-Fc fusion proteins, polynucleotides encoding these insulin-Fc fusion proteins, and pharmaceutical formulations of exemplary insulin-Fc fusion proteins are provided, in addition to methods of use and preparation.