title: 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.
authors.affiliation: Research Centre, Agriculture and Agri-Food Canada, Lethbridge.
authors.forename: R B
authors.initials: RB
authors.lastname: Cook
authors.forename: J D
authors.initials: JD
authors.lastname: Popp
authors.forename: J P
authors.initials: JP
authors.lastname: Kastelic
authors.forename: S
authors.initials: S
authors.lastname: Robbins
authors.forename: R
authors.initials: R
authors.lastname: Harland
mesh_terms: D000822:Animal Husbandry / Q000379:methods; D000818:Animals; D001835:Body Weight; D002417:Cattle / Q000254:growth & development*; D007987:Gonadotropin-Releasing Hormone / Q000276:immunology* / Q000502:physiology; D008297:Male; D008460:Meat / Q000592:standards*; D011897:Random Allocation; D011993:Recombinant Fusion Proteins / Q000276:immunology; D012098:Reproduction / Q000187:drug effects; D013737:Testis / Q000254:growth & development*; D013739:Testosterone / Q000097:blood; D014611:Vaccination / Q000662:veterinary*
chemical_list: D011993:Recombinant Fusion Proteins; D007987:Gonadotropin-Releasing Hormone; D013739:Testosterone