Fusion protein for immunocastration (Sequences la and Ib) that comprises the primary amino acid sequence of the gonadotrophin-liberating protein fused to a theoretical sequence:Sequence la NH2-QHWSYGLRPGGPPFSGGGGPPFSA-COOH (SEQ ID NO: 1)Sequence Ib NH2-GPPFSGGGGPPFSAQHWSYGLRPG-COOH (SEQ ID NO: 2);DNA sequences coding for said fusion protein; vaccine comprising said fusion protein; use of the fusion protein for mammal immunocastration; process for producing the vaccine; process for preparing the fusion protein that comprises fusing the amino acid sequence of the gonadotrophin-liberating hormone (GnRH-I) to a theoretical glycosilable sequence having immunogenic activity that does not include pathogen or “carrier” protein sequences in its structure.