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Southern Illinois University, Carbondale 62901 and U.S. Department of Agriculture, Clay Center, NE 68933
Abstract
Forty crossbred boars were equally divided into eight groups at birth. Four groups were immunized (200 µg/boar) at 12 wk of age against either luteinizing hormone-releasing hormone (LHRH) conjugated to human serum globulin (LHRH-hSG) in complete Freund's adjuvant (CFA), LHRH-hSG in muramyldipeptide adjuvant (PEP), procine luteinizing hormone (LH) conjugated to hSG (pLH-hSG) in CFA or ovine LH (oLH) in CFA. Equal doses of boosters were given in either PEP or incomplete Freund's adjuvant (IFA) at 16 and 18 wk of age. Two groups of boars were immunized with either hSG + CFA or hSG + PEP (adjuvant controls). Two groups were castrated either at the time of weaning (castrate weaning) or at 16 wk when immunized boars were given their first booster injections (castrate booster). All pigs were slaughtered at 24 wk of age. Serum levels of LH and testosterone (T), LHRH or LH antibody titers, as well as testicular and accessory sex gland weights and histology were determined. By wk 16, LHRH antibody titers began to rise in those boars immunized against LHRH-hSG. Luteinizing hormone-releasing hormone antibody titers on wk 18, 20 and 22 were greater than those at wk 16. By 22 wk of age, LHRH-hSG boars had non-detectable plasma LH and T and reduced weights of testes and acessory sex glands. Boars immunized against oLH did not respond to treatment, whereas pLH-hSG boars showed a reduction in serum T levels and accessory sex gland weights. Immunization had no effect on average daily gain, hot carcass weights or loin eye area. Animals immunized against LHRH in CFA had increased 10th rib fat (P<.05) when compared with the castrated controls, adjuvant controls and the pLH-immunized boars. The incidence of boar taint was reduced (P<.05) in the LHRH-hSG and pLH-treated boars. We conclude that LHRH immunoneutralization resulted in castration-like carcass effects in boars but had no effect on performance characteristics, with the possible exception of backfat thickness. These data demonstrate for the first time that active immunization against LHRH is both feasible and practical as an alternative to surgical castration in boars.
1 Supported in part by the Natl. Pork Producers Assoc., Acknowledgment is made to the USDA and NIAMDD for gifts of porcine and ovine LH used in this study. We also thank G. D. Niswender for the porcine LH radioimmunoassay materials.
2 Reprint requests: Dr. Richard E. Falvo, Dept. of Physiol., School of Med., Lindegren Hall, Southern Illinois Univ., Carbondale, IL 62901.
3 Dept. of Physiol., School of Med.
4 Dept. of Anim. Ind., School of Agr.
5 Roman L Hruska U.S. Meat Anim. Res. Center, Agr. Res. Serv.
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