Mismating
December, 2000
Occasionally, even a careful dog owner has to deal with an
unwanted pregnancy. A male dog’s persistence getting to a
bitch in heat can overcome our best efforts to prevent an
unintentional breeding.
Several options exist for dealing with this problem. If its not
imperative to use this particular bitch for future breedings or
she’s getting older and would only be bred one more time
anyway, then spaying early in pregnancy is a low risk procedure.
Another option that is usually safe for the bitch is to allow her
to go through a normal pregnancy and whelping, finding homes for
the puppies, even if they’re mongrels.
A third option, chosen frequently, is to call on your
veterinarian to terminate the pregnancy safely and effectively.
Unfortunately, a perfectly safe means of aborting a pregnancy
does not exist. The most common method used to accomplish early
abortion involves the administration of high doses of estrogen.
This is the hormone that naturally predominates in the female’s
body during a normal heat. Just before ovulation, estrogen
normally decreases and progesterone becomes the predominant
hormone. Progesterone is required to maintain a healthy
pregnancy. Giving estrogen by injection or pills can extend the
heat period and end the pregnancy. In order to be effective, it
must be given within 5 days of breeding. The two common forms of
estrogen used by veterinarians are estradiol cypionate, or ECP,
and diethylstilbestrol or DES. Side effects are less common with
DES, but the drug can be difficult to obtain.
Several serious side effects are possible with the use of
estrogen. It can suppress the bone marrow’s production of
red blood cells. Rarely, this results in a severe, prolonged or
permanent anemia that leads to death. A more likely, but still
rare, side effect is pyometra, bacterial infection of the uterus,
This is also life-threatening and does not respond to antibiotics
alone. Most dogs with pyometra will respond to injections of the
hormone prostaglandin (Lutalyse), but the infection is expected
to recur after future heats unless the bitch becomes pregnant.
Most dogs that develop pyometra are simply spayed
Other drugs have been used to induce abortions in early, middle,
and late pregnancy Prostaglandin injections given every day for
4-11 days are about 80 percent effective and nearly always cause
gastrointestinal side effects. The longterm effects on the dog’s
fertility are not fully understood Dexamethasone, a common
corticosteriod given daily can also reliably terminate a
pregnancy, but is also not considered safe enough to recommend
its use.
In conclusion, there is no perfectly safe method of terminating a
pregnancy after mismating has occurred . As is usually the case,
the best treatment is prevention .The real solution is better
management of the bitch in heat to avoid unintentional breeding,
in the first place. Estrogen administration is an effective means
of early abortion, and the side effects are rare. But when they
occur, they can be life threatening When faced with the problem
of an unwanted pregnancy, a thorough discussion with your
veterinarian is recommended.