EFFECTS OF IMMUNIZATION AGAINST GNRH UPON BODY GROWTH, VOLUNTARY FOOD-INTAKE AND PLASMA-HORMONE CONCENTRATION IN YEARLING RED DEER STAGS (CERVUS-ELAPHUS)

Red deer stags in New Zealand were given a series of immunizations aga inst GnRH at 9-12 months of age (spring/early summer) in 1989 and 1990 and the effects upon plasma concentrations of luteinizing hormone (LH ) and testosterone during the rut (15-17 months; autumn) and upon body growth to slaughter at 22 months (spring) were studied in two experim ents. Control animals showed a sharp peak in plasma LH and testosteron e concentration during late summer/early autumn, just preceding the ru t, with scrotal circumference increasing to a maximum during the rut; body growth stopped during the rut in Expt 1 but not in Expt 2. Immuni zation caused the development of significant antibodies against GnRH d uring late spring and summer, and reduced but did not eliminate the in crease in plasma LH and testosterone and scrotal enlargement leading u p to the rut. Immunization did not affect body growth or voluntary fee d intake during the rut in either experiment, but in Expt I early immu nization significantly increased growth during both the pre-rut and po st-rut periods. Immunization did not effect dressing out percentage, s lightly increased carcass fatness in Expt 1 but not Expt 2, and reduce d velvet antler growth by 12 months of age.