Advances in canine contraception

Caroline Coile, Ph.D., is a breeder, owner and handler of top-winning Salukis and the author of 19 books, including The Barron’s Encyclopedia of Dog Breeds,
andCongratulations! It’s a Dog! Buy at Amazon.com.

Responsible breeders spend more time preventing litters than producing them, but it’s not easy when they share their homes with intact dogs and bitches.
Lectures about abstinence, saving oneself for the ideal mate, or waiting until obedience school graduation fall on deaf ears. What’s a breeder – who
doesn’t want to be a breeder lust yet – to do?

In the face of raging hormones, most not-now breeders resort to the barrier method of birth control. When dog people talk about the barrier method of contraception,
they usually mean a locked door or strong fence. These are pretty effective, but not foolproof. In fact, it’s that “fool” part that is responsible
for turning many a notnow breeder into an accidental breeder

Beyond keeping dogs apart, many methods have been tried. Barrier methods similar to those used in humans have not been effective. Dogs simply refuse to
wear condoms. Intravaginal devices to prevent penetration were once marketed for dogs, but were neither sufficiently safe nor effective. They were
difficult to fit to different sizes of dogs, and sometimes caused vaginal infections or tears to the vaginal walls. Intrauterine devices have not worked
because it’s too difficult to pass such a device through the canine cervix. Recently, however, an Italian study described an intrauterine device for
canine contraception that prevented pregnancy and had no side effects over the two-year period it was tested. Such devices don’t prevent estrus, however,
which is a major part of the nuisance factor of an intact bitch.

Permanent Sterilization

Surgical sterilization prevents both estrus and pregnancy. In bitches, that usually means an ovariohysterectomy, in which the ovaries and uterus are removed.
Less often, only the ovaries are removed, leaving the uterus. This method is not as popular because the chance of pyometra (uterine infection) persists;
howeve, pyometra does not occur often in such dogs. Tubal ligation, in which the oviducts are tied off, is seldom performed because it does not prevent
estrus.

Surgical sterilization of males typically means castration, in which both testicles are removed. A vasectomy, in which the testicles remain but the vas
deferens is cut or tied, is seldom performed because it leaves unwanted male behaviors, such as attempting to mate, intact.

Because surgical sterilization entails some discomfort and slight risks, researchers have long sought less invasive methods. The Alliance for Contraception
in Cats & Dogs (www.vetmed.vt.edu/ACCD) was formed in 2000 to promote the development of non-surgical
methods of sterilization. In 2003, the Food and Drug Administration approved the first product for chemical sterilization in male dogs ages 3 to 10
months. The drug, zinc gluconate neutralized by arginine (Neutersol), is injected into each testicle, shrinking the testes and prostate, and preventing
the production and transport of sperm. Side effects are minimal, but may include ulceration at the injection site if the dog moves during injection,
or if the drug is not properly injected. Because the testes are not removed, some testosterone still remains. This means the procedure may not prevent
testosterone-related disease, or some male behaviors such as roaming and marking. Neutersol is marketed by Addison Biological Laboratory, in Missouri
(www.adclison/abs.com).

Current studies have centered on immunocontraception, in which vaccines stimulate the production of antibodies that interfere with gamete production or
fertilization. Vaccines against luteinizing hormone (LH) or gonadotropin-releasing hormone (GnRH) have not yet been satisfactory. There is some promise
in vaccines against luteinizing hormone releasing hormone (I.HRH), and against eggcoating proteins. Most research has centered on these egg-coating
(zona pellucida) vaccines, which produce antibodies that bind with eggs and interfere with fertilization by sperm. Such vaccines have been effective
in several species, including dogs. Unfortunately, side effects may include development of cystic ovaries.

Temporary Contraception

Many breeders aren’t looking for permanent sterilization, but need a means to postpone estrus or prevent pregnancy temporarily. Although dogs don’t have
“the pill,” hormonal contraceptives similar to those used in women have been investigated.

Hormone administration is the most widely used temporary method of estrus suppression. Hormones for the prevention of estrus are of two types: synthetic
forms of the female hormone progesterone, which is associated with pregnancy; and forms of the male hormone testosterone.

The most well-known synthetic form of progesterone is megestrol acetate (Ovaban). It’s given either during the month preceding an anticipated estrus, or
during the first week of estrus. It suppresses estrus more than 90 percent of the time, and most dogs have a subsequent estrus 4 to 6 months later.
Its use is associated with some side effects, such as weight gain, lethargy, or restlessness, as well as with an increased risk of pyometra. Most breeders
consider the risks to outweigh the benefits.

Although long-acting or implant able contraceptives are popular in women, they have not been satisfactory in bitches. Medroxyprogesterone acetate (Depo-Provera)
has been used in Europe as a canine contraceptive, but is associated with an increased risk of uterine disease.

The most well-known testosterone-based drug is mibolerone (formerly marketed as Cheque), a liquid androgen given daily to suppress the onset of estrus.
After discontinuing treatment, most bitches return to estrus in a couple of months. Its side effects include clitoral enlargement, increased aggression,
and liver disease. Mibolerone is now difficult to buy in the United States because it was abused by human bodybuilders, and also had a comparatively
small veterinary market.

Testosterone, oral or injectable, is routinely given to racing Greyhounds to prevent estrus. It has the same side effects as mibolerone. Because it also
improves racing performance, its use is controversial.

Fewer choices are available for male dogs. A six-month contraceptive implant for male dogs was approved last year in Australia and New Zealand. The drug,
deslorelin acetate (Suprelorin), prevents GnRH from signaling the pituitary gland to make other hormones needed for testosterone and sperm production.
The drug is implanted with a syringe, similar to how a microchip is implanted, and is released slowly over several months. Its effects are reversible.
It was developed by Peptech Animal Health (www.peptech.com), which is working on a 12-month form and is hopeful
that it will eventually reach U.S. markets.

Researchers are optimistic that within the decade several non-surgical choices will be available for the prevention of pregnancy. Although most of their
efforts are aimed at permanent solutions, it’s likely that newer temporary solutions will also become available. Meanwhile, bar the doors!

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