GonaConTM Trial in Bull Calves 2

Summary

​This project is a continuation of Project B.AWW.0194.A which investigated the efficacy of the immunocontraceptive vaccine GonaCon™ to (1) induce antibodies against the key reproductive hormone gonadotrophin releasing hormone (GnRH) in bull calves and (2) suppress testicular growth longer-term. In Project B.AWW.0194.A it was found that at 12 months after secondary vaccination Brahman bulls still had suppressed testicular growth. In the current project the monitoring of testicular growth was continued in a subset of control bulls (n = 4) and vaccinated bulls (n = 8). At approximately 21 months after secondary vaccination, five vaccinated bulls continued to have a smaller (P < 0.01) testicular diameter (42.0 ± 1.5 mm) compared with control bulls (73.8 ± 3.1 mm) whilst three vaccinated bulls had a testicular diameter (67.0 ± 2.6 mm) approaching that of controls. The latter three vaccinated bulls started to undergo faster testicular growth between approximately 15 and 17 months after secondary vaccination. The project has shown that GonaConTM can induce an immunocastration condition for up to 18 months in bulls. A proportion of vaccinated bulls have suppressed testicular growth for a longer period.