As we now know from the reproductive physiology of the doe, the sequence of events of the estrous cycle starts with the production of GNRH. The production of GNRH stimulates the secretion of FSH and LH. The increased level of FSH stimulates the development of follicles with subsequent increased estrogen secretion. The increased estrogen level causes a decrease in FSH and an increase in LH. The increased LH comes in a pulse and causes the follicle to ovulate and release the ovum. This causes the female to enter “estrus” or “standing heat”.

Now lets take a closer look at the roles estrogen, testosterone and fall/winter metabolism plays on the mating and social ranking of white-tailed deer.

Estrogen
Once the doe’s come into their estrous cycle they produce vaginal secretions (including estrogen) that the bucks are able to smell. These vaginal secretions may be detected on the doe, or more likely in the urine the doe passes and leaves behind. Some researchers believe that bucks may come into breeding readiness when they perform the flehmen sniff and detect estrogen from a doe’s urine, and that this detection may ensure that both the bucks and does are ready to breed at the same time. This suggests that bucks may respond to estrous secretions or estrous urine as long as their testosterone levels are high, which may be as early as late August or early September, until after most of the does have been bred.
Bucks show interest in urination of females particularly during the rut and follow their investigations with a lip curl (Flehmen). Although somewhat ritualized, the purpose of the lip curl is to expose the scent to the vomeronasal or Jacobson’s organ, which assists the buck with his assessment of the doe’s reproductive stage and willingness to mate by the estrogen levels in her urine. The vomeronasal organ detects large non-volatile molecules. Because it has separate tracts to and stimulates different areas of the brain, it is properly considered the ‘sixth sense’.


Testosterone
It has been shown that a buck's testosterone level rises in the fall, and that dominant bucks have higher testosterone levels than subdominant bucks. Researchers have suggested that does can smell testosterone and protein levels in a buck's urine, and are able to determine the health of the buck by the smell; which allows the does to choose a healthy dominant buck to breed with. If this is true, urine from a healthy dominant buck should attract does, which may in turn attract bucks.

Since testosterone levels rise when the bucks begin to shed their velvet and make rubs and scrapes, and remains high as long as doe’s remain in estrous, urine with testosterone can be used throughout the rut. A buck in rut is curious about which other bucks are in its area, and may be compelled to check out any new buck scent in the area. However, because high levels of testosterone are associated with dominance, buck in rut urine may attract dominant bucks, but it may scare off subdominants.

Fall Metabolism Effects on the Buck
The higher protein levels in a buck’s urine, along with testosterone levels, give males their strong eye-watering rutting odor. As they stop feeding and mobilize fat, highly volatile ketones resulting from incomplete oxidation of fat appear in the urine. Odor therefore indicates quantitatively how hard the male is rutting and whether he is ‘spent’. The message may be significant tothefemales when selecting a mateand also to other males. When a dominant buck has an essence of being “spent” but with a strong essence of testosterone, it is more likely that a harder rutting buck in the area will investigate the scent and try to run the “spent” buck from the area. This is the distinction buck’s use to determine the over-all stamina of each other, hence the rub-urination before a full-blown fight.


Is all this making sense so far?