Effect of active immunization against GnRH on testosterone concentration, libido and sperm quality in mature AI boars

The trial period lasted for 15？weeks and was divided into four periods: Control period: three weeks before vaccination; Period I – four weeks after first vaccination; Period II – four weeks after second vaccination, Period III – four weeks after third vaccination. Blood and sperm samples were collected at weekly intervals. Freshly collected sperm samples were analyzed.Testosterone concentration correlated with libido (r？=？0.531; p？<？0.001), volume of ejaculate (r？=？0.324; p？<？0.001) and the percentage of morphologically normal spermatozoa (r？=？0.207; p？<？0.05). Testosterone concentration rised significantly (p？<？0.05) in 5–6？week of trial, e. i. after the first dose of Improvac and after this peak the level of testosterone further progressively decreased (p？<？0.05).Results from this study indicate that active immunization of sexually matured boars against GnRH has negative impact on testosterone concentration, sexual behavior, volume of ejaculate and total number of normal spermatozoa in ejaculate.