The effects of immunization against luteinizing hormone releasing hormone (LHRH) on body growth and carcass characteristics in Karaka ram lambs were investigated using recombinant LHRH fusion proteins. Recombinant fusion proteins, ovalbumin-LHRH-7 and thioredoxin-LHRH-7, were produced using recombinant DNA technology and expressed in E. coli. The control group (C, n = 5) was injected with ovalbumin and thioredoxin recombinant protein mixture, the immunization group (1, n = 6) was injected with a ovalbumin-LHRH-7 and thioredoxin-LHRH-7 recombinant fusion protein mixture (anti-LHRH vaccine) and, ram lambs in the elastrator group (E, n = 5) were castrated using elastrator bands. Animals in each group were weaned at 17 weeks of age and injected (primary immunization) with either mixture at 18 weeks of age or castrated. The C and I groups received a booster immunization 8 weeks later (26 weeks of age). Animals were housed in groups, weighed every 2 weeks and slaughtered at 36 weeks of age. Carcass of slaughtered lambs were chilled for 24 h at +4 degreesC and evaluated for carcass characteristics. Immunization did not reduce growth rate and live body weights. Immunization and castration had no effect on carcass measurements and loin eye muscle area, hot and cold carcass weights, dressing percentage and wholesale cuts. Immunization against LHRH reduced testis weight and immunized animals had leaner carcasses than castrates. It was concluded that immunizing ram lambs against LHRH using new recombinant LHRH fusion proteins could be an alternative to physical castration to improve carcass quality in ram lamb production; however, further research is required to determine the effective immunization and slaughter age to improve carcass traits. Published by Elsevier Science B.V.