Dr. Bruce Eilts, a reproductive specialist at Louisiana State University School of Veterinary Medicine, answers this week's questions.

Question: We've heard some forms of birth control are used on some species, such as elephants in South Africa, in which it would be too difficult to surgically remove reproductive organs. How often is some form of birth control -- other than spaying -- used in female dogs and cats? Is there a criteria?

Answer: Controlling the estrus cycle in dogs is not a very common practice. Most dogs that are used for breeding should be bred at a relatively young age. Those dogs not intended for breeding should be sterilized (ovariectomy or ovariohysterectomy) before their first estrus (heat).

The need to go through heat or to have a litter of puppies to 'make the dog a better pet' are unfounded. There now are no drugs specifically marketed by pharmaceutical manufacturers to control estrus in the dog, although there have been several in the past. Compounding pharmacies can make these products at the request of a licensed veterinarian.

Question: What does it involve? Pills, patches, shots?

Answer: Products that were marketed in the past included pills, oral liquids and injections. These can still be obtained by licensed veterinarians.

Question: How do these products work?

Answer: Knowledge of the dog's reproductive cycle is needed to understand how these products work.

The dog comes into estrus (heat) about every six months. During heat, estrogen, secreted from the follicles, is the dominant hormone. Estrogen causes the signs of heat such as attracting males and causes the vaginal bleeding.

After the eggs are released (ovulation) from the follicles, the follicles change from estrogen production to progesterone production and the dog enters a phase called diestrus.

Progesterone is the hormone needed to keep the female pregnant. Progesterone causes changes in the uterus that maintain pregnancy.

Whether or not a dog is pregnant, whether or not she is bred, every time she comes into heat she will produce progesterone for about two months after heat. The production of progesterone for these two months keeps the dog out of heat.

After the two months of progesterone production, the dog goes into a three to five month period where there are no reproductive hormones secreted (anestrus).

The drugs available to control estrus are generally either progesterone-like drugs that mimic the time of normal progesterone, or an androgen that prevents estrus.

Question: Is there an advantage to using these kinds of birth control?

Answer: The greatest advantage in using these products is to stop or delay estrus when some upcoming events are likely to coincide with the anticipated onset of estrus. If an event such as a show or field trial is upcoming and the last estrus was about five to six months ago, then the upcoming estrus can be postponed effectively with these hormones. Because the dog is out of estrus for five months out of six, the long term use of drugs is really not needed. If the dog was in heat last month and an event is next month, there is almost no chance that the dog would come into heat for the event.

Question: How do these methods affect the health of a female dog's reproductive organs?

Answer: Short term, the drugs are generally safe; however, long-term effects, depending on the drug, include mammary tumor development, diabetes mellitus, several hormonal disorders, mucometra (fluid in the uterus), pyometra (pus in the uterus) and cystic endometrial hyperplasia (a uterine disorder) with progesterone like drugs.

Testosterone-like drugs can cause aggression, clitoral enlargement, anal-gland problems and excessive tearing from the eyes.

Question: Are there disadvantages?

Answer: There are more disadvantages than advantages in trying to control heat in the dogs with drugs. The majority of time the drugs are not needed anyway, so using the drugs is wasting money and potentially jeopardizing the dogs health. If long-term drug use is employed to keep the dog out of heat, potentially serious side effects are likely.

Question: We know veterinary services can freeze and bank sperm for future use via artificial insemination. Is there any equivalent practice for banking unfertilized eggs?

Answer: Assisted Reproductive Technology in the dog is not nearly as advanced as in the farm-animal species. Artificial insemination with fresh, cooled and frozen semen is commonly practiced. Embryo transfer (the use of a surrogate mother for eggs harvested from a desired donor) is common in horses and cows, but very rarely performed in the dog.

This is primarily a result of the difficulty of harvesting the eggs without performing surgery, and having a surrogate mother at the correct stage to accept the eggs.

In vitro fertilization is not being performed in dogs, again because of the difficulty of harvesting eggs and maturing the eggs to correct stage for fertilization.

Freezing eggs is not being done. There are some facilities that do offer cloning of dogs, however it is expensive and difficult to do. There are companies that can harvest skin from a dog a preserve it for future cloning, if it becomes more affordable.

Dr. Bruce Eilts

Eilts graduated from the University of Minnesota's College of Veterinary Medicine in 1977 and completed a master's degree and residency in theriogenology in 1982. He returned to private practice before becoming an assistant professor at Louisiana State University in 1984. He became a Diplomate in the American College of Theriogenologists in 1986. He now is a professor of theriogenology at LSU's School of Veterinary Medicine. The primary focus of his work at LSU are equine and canine reproduction.

Read our past Q&As:
Veterinary Q&A: How to find a good vet
Veterinary Q&A: Neutering your dog Part 2
Veterinary Q&A: Neutering your dog Part 1
Veterinary Q&A: Hyperthyroidism in cats
Veterinary Q&A: Incontinence in dogs
Veterinary Q&A: Hanging tongue syndrome
Veterinary Q&A: Bad breath in dogs
Veterinary Q&A: How much is too much exercise for my dog? Part 2
Veterinary Q&A: How much exercise does my dog need? Part I
Veterinary Q&A: A killer called bloat
Veterinary Q&A: Initial care for new puppies
Veterinary Q&A: Knee problems in dogs
Veterinary Q&A: Flea-control treatment
Veterinary Q&A: Bearded dragon lizards
Veterinary Q&A: Vaccinations for indoor cats
Veterinary Q&A: Lumps and bumps
Veterinary Q&A: More on aging dogs and arthritis
Veterinary Q&A: Aging dogs and arthritis
Veterinary Q&A: Puppy and geriatric exams
Veterinary QA: What dogs can safely chew
Veterinary QA: Why does it cost so much to clean a dog's teeth?
Veterinary QA follow-up: More on cleaning a dog's teeth
Veterinary QA: When to spay or neuter

Do you have a question about pet health? Ask now! We'll pose some of your questions to a local vet in an upcoming post.