Changes in blood content and histology during growth of antlers in red deer (Cervus elaphus) and their relationship to plasma testosterone levels.

Antlers were removed sequentially from 18 mature red deer stags between 28 and 112 days after casting of the previous hard antlers and the blood volume determined and structure investigated histologically. One antler from each stag was removed during the growth phase, the other at velvet shedding. Antler blood volume increased linearly, with increasing antler weight at a rate of 194 ml/kg between 28 and 91 days after casting but subsequently declined rapidly. A zone of mineralisation occurred between 5 and 10 cm below the antler tip until 91 days but was subsequently markedly reduced in size and replaced by bone. Between 91 and 112 days growth slowed and a rapid increase in formation of compact cortical bone occurred in the periphery of the whole antler. These changes were associated with increasing circulating levels of testosterone.