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.


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