As a fetus, a colt's
testes move from a position inside the abdominal cavity through
a space called the inguinal canal. By the time the foal is two
weeks of age, this process is completed. Sometimes, one or both
(usually one) of a colt's testicles will not descend properly.
When this occurs the colt is most commonly referred to as a 'cryptorchid',
but my also be called a 'rig' or 'ridgling'.
The retained testicle
(or testicles) does not produce fertile sperm but does produce
testosterone. Because the testosterone is still being produced,
when the horse reaches puberty (usually around 12 - 18 months
of age) he will exhibit 'stallion like' behavior. At this stage,
the horse will also be capable of breeding mares. Whether or not
the stallion is fertile will depend on whether or not one or both
testes are retained. If only one is retained, the second testicle
will most likely be fully functional and the stallion will be
capable of impregnating mares.
There are four types
of cryptorchidism:
Complete abdominal retention
is when the the testicle is if fully retained in the horse's abdomen
and is mobile within the abdominal cavity. It is highly unlikely
that the testicle in such a case will ever produce sperm, although
there has been one case reported. The sperm however would not
be fertile.
incomplete abdominal
retention is when the retained testicle is not mobile within the
horse's abdominal cavity. It is usually located near the deep
inguinal ring, with portions of the attached tissue of the testicles
passed through the vaginal ring where they may in some cases be
externally palpated when the horse is standing or lying down.
Permanent inguinal retention
is when the testicle has descended through the deep inguinal ring
but is trapped within the inguinal canal. It is very difficult,
and in some cases impossible to palpate. Either or both testicles
may be retained. A horse with permanent inguinal retention is
sometimes referred to as 'high flankers".
In a case of Temporary
inguinal retention, the retained testicle is is palpable when
the horse is laying down, and may also be palpable when the horse
is standing. In this case, the testicle will usually descend on
it own by the time the horse reaches the age of three years. However,
there have been cases where it has not descended until the horse
reaches six years of age. The right testicle tends to be affected
more often in this case.
In some cases the testicle may be aided by treating the horse
with hCG (human chorionic gonadotropin). This will artificially
stimulate the natural testosterone production, encouraging descent.
Any sperm produced in this case will be sterile.
Cryptorchid testes compared
with regular testes are are more likely to develop tumors. Because
of this, surgical removal of the testes is usually recommended.
A cryptorchid is diagnosed based on physical examination, including
rectal examination, and blood plasma hormone tests.
The cost of castration
for a cryptorchid is higher than it would be for a regular stallion.
It is possible that Cryptorchidism
is genetic, but there is no concrete proof and it is a widely
debated subject.
