Immunization against GnRH in Mature Mares: Antibody Titres, Ovarian Function, Hormonal Levels and Oestrous Behaviour

Abstract

The aim of the present study was to investigate the effect of active immunization against GnRH in mature Standardbred mares (three experimental and one control mare) on antibody titres, ovarian function, hormonal levels and oestrous behaviour. The mares were individually teased with a stallion once each day. During the first part of the experiment (period I: late April until November), blood was sampled every third day during the first 3 months, thereafter once per week. In the second part of the experiment (period II: December until August), sampling was carried out every second week. Progesterone, oestradiol-17beta and LH were analysed. Rectal gynaecological examination was made with the same intervals as the blood samplings and included palpation of the genital organs and ultrasonography. The experimental mares were immunized against GnRH with a GnRH-BSA conjugate. Equimune (Vetrepharm, Bracetown, Business Park, Clonee, Co. Meath, Republic of Ireland) was used as adjuvant. The mares were immunized on four occasions (20-30 day intervals) and GnRH antibody titre was determined. All immunized mares produced antibodies against GnRH but the maximum titres as well as the duration of a greater than 10% binding capacity varied between the mares (1 : 1600 to 1 : 50 000; 5 to 12 months, respectively). After the first injection, all mares showed one oestrus and ovulated at the regular time. In two of the mares, the immunization resulted in ovarian atrophy. Their hormone levels of progesterone, oestradiol- 17beta and progesterone decreased to basal levels and the cyclical hormone pattern was interrupted from approximately 30 days onwards. They continued to show oestrous signs but with irregular durations and intervals. The third mare showed ovarian suppression only for short periods and not in both ovaries at the same time; the hormone levels were basal for only about 20 days (days 50-70) and the mare ovulated on day 75 after start of immunization. The other mares ovulated after 13.5 and 15 months, respectively. It is concluded that the effect of immunization against GnRH in mature mares was individual concerning antibody titre response and the suppression of ovarian activity and hormone levels. Mares with totally inactive ovaries continued to show oestrous signs but with irregular intervals and durations.

Vaccination against gonadotropin-releasing factor (GnRF) with Bopriva significantly decreases testicular development, serum testosterone levels and physical activity in pubertal bulls

“…As it has been shown in many investigations published during the last years [3][4][5][6][7][8][9][10]17,20,[29][30][31][32][33][34] vaccination against GnRF was able to induce an increase in anti-GnRF antibody titer.…”

“…The suppression of reproductive function using an anti-GnRF vaccine has been demonstrated in numerous studies in cattle [3][4][5][6][7][8][9][10][11][12][13], sheep [10,[14][15][16][17][18][19][20][21], pig [22][23][24][25][26][27][28], horse [29][30][31][32][33][34] and in wild animals [35][36][37][38][39].…”

Suppression of testicular function and sexual behavior by vaccination against GnRH (Equity™) in the adult stallion

“…The high degree of safety when using Equity TM in horses agrees with a recently published study in mares (Elhay et al, 2007) showing that only 10 of 24 vaccinated mares reacted with a transient slightly raised and flat swelling of the skin following first or second immunization. In contrast, the application of Improvac TM or other GnRH vaccine formulations (Dowsett et al, 1991(Dowsett et al, , 1996Dalin et al, 2002) in the horse may cause severe adverse effects as pyrexia, apathy and stiffness of the neck and should therefore not be used in horses.…”

“…In horses, Schanbacher and Pratt (1985) were the first to describe the successful vaccination against GnRH in a cryptorchid stallion. Until now, several studies have been published (Dowsett et al, 1991(Dowsett et al, , 1996Malmgren et al, 2001;Dalin et al, 2002;Clement et al, 2005;Turkstra et al, 2005;Imboden et al, 2006;Elhay et al, 2007) not only investigating the anti-GnRH effect on reproductive activity in the horse but also for the treatment of equine arteritis virus (EVA) shedder stallions (Burger et al, 2004 …”

Managing a mare for breeding and sport

“…Several studies investigating the effect of GnRH vaccination have been carried out on mares, some documenting effective suppression of ovarian function and oestrous behaviour along with a subsequent reversal of these effects (Tshewang et al 1997), while others documented greater individual variation and a less reliable result (Dalin et al 2002).…”