|De avila, D|
Submitted to: Journal of Animal Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/20/2005
Publication Date: 2/1/2006
Citation: Geary, T.W., Grings, E.E., Macneil, M.D., De Avila, D.M., Reeves, J.J. 2006. Use of recombinant gonadotropin releasing hormone antigens for immunosterilization of beef heifers. Journal of Animal Science 84:343-350. Interpretive Summary: Immunization against GnRH using ovalbumin-GnRH, thioredoxin-GnRH or a cocktail of the ovalbumin-GnRH/thioredoxin-GnRH fusion proteins as antigens prevented estrous cycles in 92% of prepubertal heifers during the 26 wk experimental period. The ovalbumin-GnRH antigen resulted in the greatest GnRH antibody response and 100% of these heifers were anestrus 14 wk after the last booster immunization. Immunization against GnRH had no affect on daily gain or carcass traits, but heifers receiving Synovex H implants had increased gain and leaner carcasses with larger ribeye area. Heifers in this study received a primary and two secondary immunizations. While the ovalbumin-GnRH antigen has potential applications for preventing estrous activity and pregnancy among heifers destined for slaughter, further research is needed to facilitate the delivery system of this antigen to make it easier to apply by producers.
Technical Abstract: The objective of this study was to evaluate three GnRH antigens for immunosterilization of beef heifers. Heifers were immunized against a thioredoxin fusion protein containing seven GnRH peptides (tGnRH, n = 12), an ovalbumin fusion protein containing seven GnRH peptides (oGnRH, n = 12), a combination of oGnRH plus tGnRH (o/tGnRH, n = 12), or a combination of ovalbumin and thioredoxin (control, n = 11). Each heifer received a primary immunization containing 1 mg of protein in 1 mL of adjuvant administered in the mammary gland at wk 0 (mean age = 38 wk) and booster immunizations at wk 6 and 12. Six heifers within each treatment received Synovex H implants at wk –2. Weekly blood samples were collected from wk –2 to 26 for determination of serum progesterone concentrations and GnRH antibody titers. In GnRH immunized heifers, GnRH antibody titers increased after the first booster injection, peaked after the second, and remained elevated through the end of the study (P < 0.01). Heifers immunized against oGnRH achieved greater (P < 0.05) GnRH antibody titers than tGnRH heifers but did not differ (P = 0.20) from o/tGnRH heifers. Estrous cycles were prevented (P < 0.05) in 10/12, 12/12, 11/12 and 0/11 tGnRH, oGnRH, o/tGnRH, and control heifers, respectively. At slaughter, uterine weights were lighter (P < 0.01) for GnRH immunized heifers than control heifers. Synovex H implanted heifers had greater (P < 0.05) ADG from wk –2 to 26, greater LM area, and lesser percent kidney, pelvic and heart fat, yield grade, and quality grade than non-implanted heifers. Immunization against GnRH fusion proteins resulted in production of antibodies against GnRH that prevented estrous cycles in 92% of heifers without affecting feedlot or carcass performance. Implanting heifers with Synovex H improved ADG, LM area, and yield grade. Improvements in delivery of the oGnRH vaccine may provide a feasible alternative to surgical spaying of heifers.