Cactus deer: when antlers grow endlessly

Cactus deer syndrome is a rare condition in which male deer do not shed their antlers and continue to grow in a chaotic manner, resembling a prickly cactus. The cause is hormonal imbalances, injuries, or infections.

Named for the resemblance of the antlers to a prickly cactus, this phenomenon is caused by hormonal imbalances, most commonly associated with low testosterone levels. Normally, deer grow antlers each year, become covered in soft, velvety skin called pubescence, and are then shed when testosterone levels drop.

However, in cactus deer, this cycle is disrupted: due to testicular trauma, undescended testicles (cryptorchidism), or viral infections such as epizootic hemorrhagic disease, the antlers do not shed and continue to grow in a pubescent state. This results in massive, chaotic antlers with many short, deformed branches, resembling cactus spines.

These antlers can grow to impressive sizes, putting significant strain on the animal's neck and shoulders, making it difficult to move and leaving it vulnerable. Cactus deer generally do not engage in mating rituals or show aggression, which is explained by their hormonal imbalance, which often causes them to become sterile.

In some cases, especially in southern regions, the antlers continue to grow for years, forming tumor-like structures. This phenomenon is more common in white-tailed or black-tailed deer, but can be observed in other species, such as mule deer.