Annual cycle

Annual cycle

Red deer stags and wapiti bulls undergo profound annual cycles that revolve around mating success during the rut (or ‘roar’) in autumn. The most obvious changes involve the development of antlers each year, but there are many other changes that influence how stags are managed on the farm.

What is the rut?
The rut is the 3-4 week period of hyper-sexual activity in autumn (i.e. late March to late April) when stags actively and aggressively compete for access to hinds for mating. During this period they exhibit various sexual and combative behaviours, including ‘roaring’ (‘bugling’ in wapiti) and territorial defence of harems (hind groups) and rutting areas. Actively rutting stags invest huge amounts of energy into protecting their patch but do very little eating for 2-3 weeks. Consequently, they will lose up to 30% of their body weight over this period.

Warning: Farmed stags can be extremely aggressive to humans over the rutting period, even if they appear to be gentle at other times of the year. Be cautious around actively rutting stags. Fully antlered stags represent an extreme risk to people during the rut.

What happens after the rut?
Stags come out of the rut in late April in a rather emaciated condition, often sporting combat injuries. Generally they will just remove themselves from the rutting area, and it is often easiest to manage the process of stag:hind separation by simply opening gates into other areas of the farm. Post-rut stags go into a convalescence mode, becoming rather sedentary and lethargic…but don’t be fooled, as they can very quickly become aggressive again over the winter period…particularly if any hinds come into oestrus (heat) after the rut. Stags regain some body condition post-rut but essentially remain quite lean over winter.

On some farms it may be necessary to give stags a post-rut anthelmintic drench and provide high quality feed for them.  

As the photoperiod lengthens over late winter and spring, stags switch to a more active mode in which they dramatically increase their feed intake. During the period from about late August to early February, stags accumulate large quantities of fat in their bodies in preparation for the next rut. This period coincides with dramatic changes in testis development that control the new antler cycle.

The testis and antler cycles
Scientists have long been amazed by the profound annual changes in testicular function, and its links to the annual antler cycle, in male deer. In the case of red deer (and other deer species of northern temperate origins), the testes almost completely shut down in spring….they decrease in size, cease production of sperm and secrete only minimal quantities of the male hormone, testosterone. It is this drop in hormone production the triggers the process of antler casting in spring.

Almost immediately after casting, new antlers begin their growth cycle as velvet (non-mineralised) antler. Velvet antler exhibits a prodigious growth rate over spring and summer while the testes are in their shut-down phase. During this time stags are relatively docile and non-aggressive….and they are completely infertile.

As the photoperiod again starts deceasing after the summer solstice, this triggers a re-instigation of testes growth and sperm production. At this point, the new antlers have approached their maximal dimensions. The rising testosterone output from the testes over late summer causes mineralisation to occur inside the antlers, leading to complete hardening and stripping of outer velvet layer by late February. Testosterone also causes the stag’s neck muscles to swell….the stag is once again ready for the rut.