Active immunization with recombinant GnRH fusion protein in boars reduces both testicular development and mRNA expression levels of GnRH receptor in pituitary

Immunization using recombinant maltose binding protein–gonadotropin releasing hormone (MBP–GnRH6) altered both testicular development and transcription of the pituitary GnRH receptor (GnRHR) gene in boars. Scrotal measurement and blood samples were taken at 4-week interval after immunization at 9 weeks of age. The concentrations of testosterone and anti-GnRH antibodies in serum were determined by radioimmunoassay and enzyme-linked immunosorbent assay, respectively. The results showed that active immunization with MBP–GnRH6 increased the serum concentration of anti-GnRH antibodies (P < 0.05) and reduced the serum concentration of testosterone (P < 0.05) as compared with MBP controls. At 25 weeks of age, boars were sacrificed and testes were evaluated histologically. Testicular development was suppressed in the MBP–GnRH6 immunized animals as compared with MBP immunized boars. MBP–GnRH6 immunized pigs exhibited mounting behavior 4 weeks later than MBP immunized boars. No mature spermatozoa were observed from MBP–GnRH6 immunized animals. By real-time quantitative PCR analysis, the amount of GnRHR mRNA in the pituitary tissue was found to be significantly lower in MBP–GnRH6 immunized animals than in controls (P < 0.05). These data demonstrate that recombinant MBP–GnRH6 was effective in immunological castration in boars.