Immunization of lambs against somatotropin release inhibiting factor to improve productivity: comparison of adjuvants

Abstract

Responses to immunization against somatotropin release inhibiting factor (SRIF) were compared in lambs injected with SRIF plus either Freund's complete adjuvant (FCA), muramyl dipeptide (MDP), Freund's incomplete adjuvant/muramyl dipeptide (FIA/MDP), DEAE-Dextran (DEAE), or Quill A. By comparison with control lambs, immunized lambs grew faster and produced more wool. In lambs immunized with SRIF plus MDP or FIA/MDP, depths of back-fat and of the m. longissirnus dorsi were increased. Anti-SRIF antibody titres were very variable between groups of immunized lambs, with titres being highest for lambs injected with SRIF plus FCA or DEAE. Adverse effects of immunization were observed in lambs given FCA, DEAE and Quill A. It appears from the present study, that MDP alone or in combination with FIA would be suitable for use in commercial vaccines to enhance productivity by immunization against SRIF.