The effects of active immunization against gnRH on testicular development, feedlot performance, and carcass characteristics of beef bulls.

Abstract

The objective was to determine the effects of a recombinant fusion protein anti-GnRH vaccine on testicular development, feedlot performance, and carcass quality of beef bulls. Crossbred beef bulls (n = 58, average weight 306 kg, 9 mo of age), were randomly allocated to two groups and received either an anti-GnRH vaccine (GnRH) or placebo (Control) by intramuscular injection on d 0, 56, and 112. There were group effects (P < 0.01; as a percentage of Control) on testicular weight (53%), daily sperm production (40%), and epididymal sperm reserves (16%). There were group x time interactions (P < 0.0001) for scrotal circumference and serum testosterone concentrations; at slaughter, bulls in the GnRH group had a smaller (P < 0.05) scrotal circumference (28.3 vs 33.9 cm) and lower (P < 0.05) serum testosterone concentrations (2.2 vs 8.6 ng/mL) than those in the Control group. Average daily gain, feed intake, and feed efficiency were not different between treatments during the backgrounding phase (d 0 to 84). During the finishing phase (d 98 to 182), ADG was greater (P < 0.05) for bulls in the Control group (1.69 vs 1.42 kg/d), as was carcass weight (6.9%; P < 0.01). However, GnRH bulls had numerically better feed efficiency (6.12 vs 7.08 kg DMI/kg gain; P < 0.23) and shear force values for ribeye that were 16% lower (P < 0.14) than Control bulls, warranting further investigation. Vaccinating bulls against GnRH suppressed testicular function, with growth and carcass characteristics similar to that expected with steers.

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

“…Although it is known that testosterone has an anabolic effect, weight gain of vaccinated bulls which had low testosterone levels did not differ from control animals what is consistent with findings of previous studies [3][4][5][6]11,20]. This may be explained by the reduced physical activity in vaccinated animals improving their body condition.…”

“…At the end of the study, 20 weeks after the second vaccination, the difference between vaccinated and control animals was still 9 cm. The observation that vaccination against GnRF resulted in an impairment of testicular development was also found in previous studies in pubertal [4,13] as well as prepubertal [6,20] bulls. In the pilot experiment [13] using Bopriva ® , calves were slaughtered 3 months after the booster vaccination and histological examination of testes performed.…”

“…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.…”

“…This may be explained by the reduced physical activity in vaccinated animals improving their body condition. Moreover it must be considered, that bulls vaccinated against GnRF have carcass characteristics similar to steers and better feed efficiency than untreated bulls [4] thus increasing economic return to the beef producer.…”

“…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].…”