Why Do Bitches Miss?
Additional Article by Doc
Skinner
January, 2000
First of all, if the stud is sterile then naturally there will
be no conception. This is knowledge that the breeder will soon be
aware of and is not our primary concern here.
The main cause of a miss is due to breeding the bitch at the
wrong time of her cycle. Ninety percent of the bitches bred
between the tenth and twelfth day will conceive. Naturally this
depends on an accurate count by the breeder which may or may not
be accurate. If in doubt, have your vet do a vaginoscopy
examination.
To digress a little, the day of breeding is not always the day of
fertilization. Those instances where the breeder feels the bitch
has gone by her due date probably isn’t so. It is more
likely that her eggs were fertilized several days after the
mating. Eggs have a fertile life of two to three days. Live sperm
in some instances have been recovered from the uterus six to
seven days after the insemination. So it is no mystery that
fertilization can take place several days after the breeding. I
don’t mean to lull you into a false sense of security, a
bitch that has gone by her breeding date should be monitored
closely. Make sure the bitch continues to eat regularly. Check
the bitch’s rectal temperature every twelve hours. The
normal temperature of one hundred and one to one hundred and two
will drop to ninety-eight when she is twenty-four to forty-eight
hours from delivery. Many bitches will not eat one or two days
before delivery, so it is essential to do the temperature check;
a fever could mean problems.
Since only one sperm can fertilize an egg, why is a high sperm
count necessary? Foremost is the fact that the sperm give off
hyaluronidase, an enzyme that digests the outer coating (shell)
of the egg, enabling the one lucky sperm to enter the egg. Also,
if the eggs are not ready for fertilization at the time of
mating, it is necessary for enough sperm to hang on and be
present when they are needed. All of the sperm are not equally
healthy, and the healthiest will live the longest.
Getting back to our initial concern of misses, in our practice we
have found that a vaginoscopy is a more accurate method of
determining the onset of the fertile period than are vaginal
smears. The gross changes of the vaginal mucosa are more
consistent than vaginal cytological events.
For those veterinarians that may be reading this article, you can
sharpen your vaginoscopy skills by examining bitches in various
stages of heat that are in to be spayed. After determining your
assessment, you can check it out when you subsequently remove the
ovaries. At the time of ovulation the vaginal mucosa is very
wrinkled and sacculated and not edematous.
For those bitches that have missed on several apparenfly good
matings, they need help. Hypothyroidism can cause infertility in
beagles. Unless the bitch can walk on water, I can’t condone
breeding hypothyroids. This has become a major flaw in the
genetic pool of brace beagles.
International Canine Genetics of Malvern, PA has developed a
progesterone assay test to pinpoint the time of ovulation. Since
our hospital is located a short distance from I.C.G. we have been
using the test for some time. Our examination of hard to conceive
bitches has resulted in a ninety percent conception rate. Why?
Because they have ovulated at abnormal times. The bitches that
have not conceived may not be ovulating at all. We had one
standard poodle that ovulated on the twentieth day of heat. In a
case such as that several tests were necessary because you are
looking for the sharp rise in progesterone level which occurs at
the same time as the L.H. surge. The L.H. surge being the trigger
for ovulation. Ovulation occurs two days after the L.H. surge.
Once the eggs are released it takes two more days of maturation
to reach the fertile stage. So the proper time for breeding is
four to six days after the sharp progesterone rise.
I.C.G. also freezes semen for use even after the sire is no
longer available. I mentioned this to Joe Howard at the time and
he had Bad Jack’s semen collected and frozen so it is
possible for some breeders to have a litter of Bad Jack pups ten
or fifteen years from now.
As a closing note of interesting, but probably worthless,
information, fetuses in the right or left horn of the uterus do
not necessarily come from the adjoining ovary. Before eggs
implant in the uterus, they can travel freely from one horn to
the other; during this period of embryological development they
receive nutrition from the uterine secretion known as uterine
milk. When it is time for the eggs to implant in the uterine
mucosa, they do so at whatever location they may be at the time.
It is during this time prior to implantation that mismating
injections are most effective, but that’s another can of
worms.