Abstract: Novel modified or derivatized recombinant animal somatotropins. Methods for stabilizing recombinant animal somatotropins by modification or deletion of the Cysteine residues utilizing site directed mutagenesis to replace from one to four of the cysteine amino acid residues of said somatotropins with one or more different amino acid residues or by derivatization of (1) both cysteine amino acid residues in the small loop of said somatotropin, both cysteine amino acid residues in the large loop or the four cysteine amino acid residues in both loops of said somatotropin.

Abstract: The present invention is directed to antibodies, in particular monoclonal antibodies, which specifically bind to somatotropin binding proteins of animals, but not with the corresponding somatotropin receptors. The antibodies may be used alone to enhance the growth of animals, or may be used together with somatotropin to potentiate the effect of somatotropin in animals. The antibodies may also be used to assay the level of somatotropin binding protein of animals.