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

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Abstract
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 titer; only the animal with the highest titer developed antlers that resembled those of a castrate and remained in velvet for > 6 mo. In Oct., 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 .mu.g ovine LH [luteinizing hormone]. The immunized stags showed no rutting behavior in the autumn. The changes in the testes confirm that the immunizations were effective in blocking the secretion of the gonadotropic hormones. The redevelopment of antlers in these animals indicates that gonadotropins are not directly involved in stimulating antler growth.