Regarding the stag, Older stags do drop first in August to early Sept with others depending on age and body condition following on until everyone has cast including spikers which will be last and finished by the end of Oct.
For your chap to be so late he must have had a tough winter and lost a lot of weight. His body not having the reserves to initiate antler growth as well as recovering the body weight that he had lost, so it has delayed casting until he has a surplus of feed going through his system.
What was he like from a health perspective when he was gutted ? Any liver fluke, lung abnormalities etc ? In the photo he looks fine, just a late casting last years spiker that grew brow tines. Stags get a black waxy line between the pedicle and the antler coronet just before they cast
Great shooting by the way
Bookmarks