Atresia is the absence of a normal opening. Therefore, choanal atresia is the lack of a normal opening at the choanae. There normal opening is absent because the bone or membrane present during embryonic development fails to break down . A recent study supports the fact that this defect is heritable, but it has not been definitively proven yet. Regardless, both parents of a cria with choanal atresia should be removed from the breeding pool and not just bred to different animals.
Choanal atresia creates a dead end at the back of the nasal passages.
The blockage of the choanae may be partial or complete or on one or both sides. With complete blockage on both sides, no air can be breathed in through the nose to reach the lungs. Air can only reach the lungs by way of the mouth. Llamas are obligate nasal breathers and must be able to breath through their nose to survive. This is especially a problem for newborns.