Effects of immunization against gonadotropin releasing hormone on reproductive functions in male rusa deer (Rusa timorensis)

Abstract

We performed an evaluation of the effect of gonadotropin releasing hormone (GnRH) vaccine on male rusa deer reproductive function. Mature male rusa deer (Rusa timorensis) were divided into two groups: untreated group (n=3) and treated group (n=7). The treated rusa deer were administered with two ml of the GnRH-protein conjugate vaccine (Improvac^®; 200 μg/ml). The vaccine was injected subcutaneously into the treated group three times at four-week intervals (April, May and June) and an additional single dose booster was given after a decrease in GnRH  antibody levels was detected (October). Blood testosterone concentrations and GnRH antibody titer were determined before the vaccination. Following that, a series of blood collection and evaluation was done for one year. In addition, we conducted a series of semen collection and evaluation, testicular size measurement and antler development recording in all deer for one year. Our results indicated that the level of GnRH antibody significantly increased (p<0.05) compared with the pre-vaccinated level. The antibody titer reached peak concentrations after the third vaccination. The high level was maintained for twelve weeks and then gradually declined to baseline. The antibody titer increased again after the fourth vaccination. The testosterone concentrations had no significant difference between the groups and times. However, the testosterone level in the treated group showed a negative correlation with GnRH antibody titer (R=-0.25). The average of testicular size of the treated group was smaller than that of the untreated group (p<0.05). The semen quality of the treated group started to decline after the third vaccination (p<0.05). Then, after the fourth vaccination, azoospermia was detected. In this study, six stags in the treated group shed their hard antlers immediately after the third vaccination. Although regrowth of velvet was observed, it did not harden. In conclusion, the GnRH vaccination in male rusa deer resulted in the increase in GnRH antibody titer, which negatively correlated with blood testosterone. The decrease in blood testosterone might be involved in the lower semen quality and poor antler development.