Antler growth in male red deer (Cervus elaphus) after active immunization against LH-RH

Four sexually mature male red deer were actively immunized against LHRH and this caused 3 of the animals to cast their antlers prematurely in the autumn instead of the spring. Development of new antlers was initiated after casting, but the effects on the antler cycle were variable and correlated with the antibody titre, only the animal with the highest titre developed antlers that resembled those of a castrate and remained 'in velvet' for more than 6 months. In October, when all the immunized deer had peak circulating levels of LHRH antibodies, the testes were reduced in size compared to the maximum values of the controls. The blood levels of testosterone were reduced in the immunized animals, and there was a minimal increase in the circulating levels of testosterone in response to an i.v. injection of 100 micrograms ovine LH. The immunized stags showed no rutting behaviour in the autumn. The changes in the testes confirm that the immunizations were effective in blocking the secretion of the gonadotrophic hormones. The re-development of antlers in these animals indicates that gonadotrophins are not directly involved in stimulating antler growth.