There was a discussion about this some time ago. Here is the excerpt with what I believe is the best explanation:
Pete wrote:Hi Folks,
These terms are often used interchangeably in rather general terms but there are subtle differences:
CRYPTORCHID: Is an inheritable trait where one or both testicles fail to descend into the scrotum. One affected testicle is a UNILATERAL CRYPTORCHID and both is a BILATERAL CRYPTORCHID.
An abdominal cryptorchid retains the teste(s) in the abdominal cavity and shortly after birth they won't be able to descend. A bilateral abdominal cryptorchid will be sterile.
Am inguinal cryptorchid retains the teste(s) in the inguinal canal (between the inguinal ring and the scrotum) and they may descend on their own or with surgery. A unilateral inguinal cryptorchid may end up with two descended testicles.
Ridgeling refers to a testicle retained near the inguinal ring (ridge) as Madelyn mentioned, so it’s meant to be a unilateral cryptorchid, possibly abdominal or inguinal but it’s commonly used to refer to cryptorchidism of any type.
Monorchidism is the absence of one (unilateral) or both testes (bilateral). It’s a rare condition.
Sperm can’t survive at body temperature so acryptorchid will be sterile unless one or more of their testicles descend into the scrotum.
Regards,
Pete
Since the occurrence of this affects only the sexual organs of male horses, it leads me to the presumption it is carried only in the male DNA complex, so can very presumably be carried from father to son. AP Indy is a ridgeling with a descended testicle..
I do not know of any studies done on pedigrees to see if, say, the son of an AP Indy daughter came out a ridgeling, with no ridgelings in his sireline.
So Run for the Roses, as fast as you can.....
