The newly grown antler is covered with a highly vascular and finely hairy thick soft skin called velvet. Depending on the physiological conditions and other factors, an antler may attain to its full growth with in three to five years of age. The newly developed antlers are tender and are highly subjected to trauma. When the antler is reached to the limit of growth, a ring of bony matter forms at the point where the antler unites with its pedicle. The bony ring gradually constricts and the blood supply cuts off to the solid bone and velvet. As blood vessels dry up, the velvet shrinks, dries and begins to peel off. Interestingly, deer rub their antlers against trees, buildings, or any other convenient projections for clearing the velvets during this period. The cleaning and hardening of antlers generally coincide with the onset of the breeding season (rutting season). This period is also characterized by maximum production of spermatozoa. The clean and hard antlers are shed after the completion of breeding season. Shedding of antler causes a small haemorrhage and shortly afterwards, a layer of cicatrical tissue appears in the form of a scar and the cycle of development of new antlers starts. The time for shedding of antler, however, varies with age, locality and feeding conditions of the animal. Young males shed their antlers earlier than older animals. The period of antler growth coincides with the seasons when the food is most abundant. High dietary protein and calcium are important for antler growth. As stated earlier that the antler cycle in deer is closely associated with the seasonal rhythm of reproduction. The cleaning of velvet occurs when the testosterone levels are high. The casting of antlers, on the other hand, takes place when the level of testosterone is very low. When the antler cycle is disturbed, it may result in premature casting, failure to shed velvet or retention of antler. In short, there are four important phases of antler cycle under the control of sexual and growth hormones. The biological data relating to reproduction are well studied in deer. The female conceives as early as her first year. The length of oestrus cycle in polyestrous species lasts for about 18-21 days. The litter size usually varies from one to two. The triplets, however, are common in water deer. The gestation period ranges from 25 weeks to 40 weeks depending on the species. The general rule is that the larger the animals the longer the period of pregnancy. The young are nursed by the mother for several months. Deer found in India include swamp deer, sambar, thamin deer, hangul, hog deer, muntjac, cheetal, musk deer and mouse deer.