Fastest-growing mammalian tissue

The fastest-growing examples of mammalian tissue are deer antlers. Composed of bone as they are extensions of the skull, but honeycombed in structure rather than solid, they are unique to deer, and can grow at a rate of up to 2.5 cm a day. Indeed, a big bull specimen of the moose Alces alces, the largest living species of deer, native to Europe and North America, can grow a full set (rack) of antlers weighing 36 kg in a single summer, adding 0.5 kg of bone each day.

Antler growth and size are influenced by genetics, but by far the most important factor is nutrition, with bucks in high-quality habitats growing much larger antlers. Deer antlers weigh 1.5–4.0 kg on average, but by the time that the antlers have attained their peak condition, during autumn, the bone tissue has stopped growing and is dead, after which the antlers are shed. In reindeer, both sexes develop antlers, but in all other deer species only the males do.