Ask questions when dog presents for mismate management
Q. Could you provide a practical review on mismate management of dogs?
AAt last year's American Veterinary Medical Association Annual Convention, Dr. Bruce E. Eilts, DVM, MS, diplomate of ACT from the Louisiana State University School of Veterinary Medicine presented an excellent review on mismate management in dogs and possible drugs used. The practical content of the lecture is provided below.
If a dog is presented for mismate management (abortion shot), several questions should be asked before any drug therapy is instituted. The answers to these questions may be:
* Was the dog really in heat?
Do a standard vaginal cytology smear to see if the dog is really in estrus. If not, then the chance of pregnancy is minimal.
* How long was the dog gone?
In that time could mating have actually happened? Since natural mating takes up to 30 minutes, a dog that is gone for only five minutes has very little chance of being mated.
* Did mating occur?
Check for sperm cells in the vaginal cytology. The presence of sperm cells definitely indicates that the dog has been mated, however, their absence does not mean that she has not been bred.
* Are puppies wanted now or in the future?
Is this really a breeding female? Why are puppies wanted? If puppies are not wanted or wanted for a groundless reason (to make the female a better dog), ovariohysterectomy may be the preferred alternative. If possible, have the owner pay for a non-estrual surgery now and then return when the dog is not in estrus.
* What are the chances the dog is actually pregnant?
In a study performed to look at pregnancy rates of dogs presented for mismate, 62 percent of dogs presented after mating were not pregnant. If ovariohysterectomy is not an option according to the owner, then waiting to determine if the dog is pregnant is probably the best alternative. Pregnancy examination can be performed by ultrasonography as early as 16 to 18 days after the first day of diestrus. If the owner wants immediate action, then some drug alternatives are available.
Estradiol cypionate (ECP) is probably the only standard mismate drug available in the United States. ECP increases the motility and facilitates rapid transport of the fertilized eggs in the oviduct and uterus and thus prevents implantation. There are very few academicians who will consider using ECP today because of the risks of adverse side effects.
When used properly and for the correct owner, however, it can be relatively safe and efficacious. The preferred dose is 44 mcg/kg (0.02 mg/lb) - not exceeding a total dose of 2 mg and given once intramuscularly during estrus. It is important that the dog is not allowed to mate again.
It is not effective if used during proestrus or diestrus; therefore, it is essential that the vaginal cytology be examined before ECP administration.
ECP can induce pyometra if given during diestrus, thus be sure the dog has not entered diestrus when ECP is administered. The dog may show side effects such as continued estrous signs, because of the estrogen influence. Cystic endometrial hyperplasia can also result after ECP administration. Bone marrow suppression can be dose-related or non-dose related. To avoid dose-related marrow suppression, do not give a second injection. Non-dose related bone marrow suppression could be totally avoided only by never giving ECP injections. Pyometra is not seen when the ECP was given during estrus; however, if given during diestrus there is an excellent chance of inducing pyometra.
If puppies are wanted in the future and the owner is aware that there is a risk associated with ECP administration and the owner is willing to take the risk, then ECP offers an inexpensive, efficacious, relatively safe mismate management. However, if the dog is a valuable breeding bitch or a surrogate child, then other alternatives may be more attractive to the owner and veterinarian.
Prostaglandins are not really a true mismate drug for dogs but can be used before pregnancy is recognized. The prostaglandin product Lutalyse (Pharmacia Animal Health) is most commonly used in the dog. Prostaglandins were originally not considered to be luteolytic until the last one-third of diestrus (40 days or more); however, it is now known that multiple injections of prostaglandins are luteolytic after only the fourth or fifth day of diestrus.
A dose of 250 mcg/kg subcutaneously daily for four days starting at day five to eight of diestrus is about 80 percent effective at inducing abortion. If the treatment fails, the pregnancy will be normal. Serum progesterone concentrations must be less than 2.0 ng/ml for 24-48 hours to result in abortion. Side effects of prostaglandins include transient vomiting, diarrhea, hyperpnea, hypersalivation and hypothermia. These side effects usually subside within 30 minutes of onset. There is also the possibility of circulatory shock, so it is important that an intravenous catheter is in place and fluids are available to manage the shock. The shock too is transient. Generally, side effects will diminish as the prostaglandin administration continues. Prostaglandin-induced luteolysis may cause some dogs to return to estrus within two to eight weeks.
If the dog is pregnant, then dexamethasone can be used. A dose of 5 mg intramuscularly twice daily for 10 days at gestation of 30 days aborted four bitches one to three days after the end of treatment. In 15 bitches, dexamethasone was given at a dose of 0.1-0.2 mg/kg orally twice daily for three doses, then 0.2 mg/kg daily on days two to five, then a decreasing dose from 0.16 to 0.02 mg/kg daily for the last five doses (total dosing done within 7.5 days). All dogs aborted or resorbed their pregnancy two to 26 days from beginning of dexamethasone treatment.
Eilts recommends just using the high dose orally twice daily until signs of pregnancy have disappeared. Just as in using prostaglandins, if medical management is blindly followed without doing pregnancy examinations, then treatment failures will occur. Normal litters have been obtained after this treatment. Side effects include a transient polydipsia/polyuria that subsided when the treatments are stopped.
Because prolactin is luteotropic and is needed to maintain normal pregnancy, prolactin antagonists will cause an abortion. These prolactin antagonists also shorten the interestrus interval and prevent mammary development.
Bromocriptine mesylate (Parlodel, Novartis Pharmaceuticals) at a dose of 30-100 mcg/kg orally twice daily for five to six days at 35 to 40 days of gestation causes abortion in three to five days. Bromocriptine may cause dogs to vomit and have inappetence, and it has not been widely accepted. The long-term effects of bromocriptine on reproduction also have not been studied.
Cabergoline (Dostinex Tablets, Pharmacia) at a dose of 5 mcg/kg orally for five days after mid-late gestation causes abortion in three to five days after treatment with minimal side effects.
A combination of cabergoline (1.0 ug/kg, two subcutaneous injections, four days apart) and an injectable synthetic prostaglandin cloprostenol sodium (Estrumate, Schering-Plough Animal Health - 5.0 mcg/kg orally daily for seven days) starting day 25 after the LH peak proved 100 percent effective and had no side effects. The treatment does cause a shortened interestrus interval.