Most of the world's supply of velvet antler comes from Sika deer, red deer and elk or wapiti, including a large deer ranching industry in New Zealand. New Zealand is the world’s largest producer of velvet, producing 450-500 tons of red deer velvet antler annually.[1] China produces 400 tons of predominantly Sika deer velvet antler annually. Russia produces 80 tons annually. United States and Canada each produce 20 tons annually.[2]
I know of no scientific evidence to support any of the marketing claims made for these supplements. I discussed your question with Tieraona Low Dog, M.D., an internationally recognized expert in the fields of integrative medicine, dietary supplements and women’s health, and an authority on botanical medicine. She explains that IGF-1 in the velvet promotes rapid growth of the antler. Dr. Low Dog notes that the two studies examining the effects of deer antler velvet supplements taken by athletes have yielded conflicting results. One showed some improvements in endurance and knee strength in weightlifters, but the other found no differences in rowers after 10 weeks of supplementation.
A systemic review on human interventions[25] makes note of a study conducted on patients of osteoarthritis (Edelman et al. 2000; cannot be located online) which found improvements in joint pain symptoms relative to baseline in the Velvet Antler group and not placebo, although a lack of information on blinding and randomization precludes results that can be drawn from this study. 
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