Nonsurgical methods of contraception in dogs and cats: Where are we now? - Veterinary Medicine
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Nonsurgical methods of contraception in dogs and cats: Where are we now?
A viable alternative to spaying and neutering for canine and feline population control is being intensively investigated. Here's a look at some possible future options.


VETERINARY MEDICINE


Gn-RH agonists

Initially, Gn-RH agonists stimulate the release of FSH and LH, thus causing estrus and ovulation, which is a disadvantage of this method. Contraception can be achieved by sustained exposure to Gn-RH agonists, which causes Gn-RH receptor downregulation of pituitary cells and decreased FSH and LH release. Thus, Gn-RH agonists can be used in males and females. These agonists have low bioavailability orally since they can be broken down by peptidases; therefore, they must be administered parenterally.5 Current formulations involve the use of slow-release devices.5

Gonazon. Gonazon (Intervet/Schering-Plough Animal Health) contains azagly-nafarelin in a controlled-release device.6,7 It received regulatory approval in the European Union in 2006. The implant is inserted subcutaneously in the umbilical area in dogs and in the neck in cats. Gonazon shows promise as a safe, long-term contraceptive in female dogs and cats, and, possibly, male dogs.

In a placebo-controlled clinical trial of 124 female dogs, Gonazon safely prevented estrus for about one year.6 In a follow-up trial, some of the bitches had the first implant removed and a second one placed. The second implant was left in place for 18 months and was 92% effective at preventing estrus.6 Gonazon reduces testosterone concentration in male dogs.6

In another placebo-controlled clinical trial, Gonazon was implanted in 10 4-month-old beagle bitches for one year, and none of them displayed estrus until after the implant was removed, whereas all of the control bitches displayed estrus during this period.7 The implantation was safe, as it was nonpainful and no inflammatory reactions occurred.

In a trial with queens, Gonazon was effective for about two years. The implantations were painless, and no side effects were noted.6

Suprelorin. Suprelorin (Peptech Animal Health) is a controlled-release implant containing the Gn-RH agonist deslorelin.8,9 It is administered subcutaneously in the interscapular region.9 It was approved for use in dogs for testosterone suppression in Australia in December 2004 and in New Zealand in September 2005.8 It was originally approved at a six-month dose but is now also available at a 12-month dose.8,9 Suprelorin is available in some European countries.4 Although Suprelorin is not labeled for use in female dogs, in one study estrus was delayed for up to 27 months.10 A similar response was found in female cats for 14 months, and there were no negative side effects.11

Gn-RH antagonists

Gonadotropin-releasing hormone antagonists function in contraception by binding to the Gn-RH receptors in the pituitary and preventing Gn-RH from binding. The advantages of antagonists are their immediate effect, and they do not cause post-treatment stimulation and estrus in females.12 The disadvantages are that antagonists require higher doses than agonists do, controlled-release systems have not been developed, and antagonists are more expensive.13

Acyline. Acyline, a third-generation Gn-RH antagonist made up of 10 amino acids, is administered subcutaneously. In male dogs, it causes a slight decrease in scrotal diameter, decreased volumes of the second and third fractions of ejaculate, decreased sperm count and motility, increased sperm abnormalities, and decreased libido and erection without local or systemic side effects.12 In female dogs, acyline prevents normal estrus and ovulation when it is administered in proestrus and terminates pregnancy in bitches about one week after it is administered at 30 to 35 days of gestation.14 Unfortunately, the duration of action in male dogs is only about two weeks.12 More research must be done before acyline is considered a viable option for long-term contraception.

4-Vinylcyclohexene diepoxide

The industrial chemical 4-vinylcyclohexene diepoxide (VCD) destroys the primordial and primary follicles in the ovaries of rats and mice via apoptosis.15 SenesTech is developing a VCD product called ChemSpay that would have the same effect in cats and dogs.15

In a study on the Navajo Reservation, 16 dogs were injected subcutaneously with VCD once daily for six days. VCD-treated bitches had significantly decreased heat behavior in the medium and high concentration dose groups vs. control. The dogs were not mated to determine whether pregnancy was prevented. At day 30 after the treatment, the bitches underwent ovariohysterectomy. Ovarian histology showed a statistically significant reduction in primordial follicles in the high-dose group for the total population and in all dose groups for puppies compared with control dogs. Blood chemistry analyses did not show any abnormalities, and the dogs were healthy 2.5 years later.15 This product shows promise as a safe and irreversible method of contraception.


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Source: VETERINARY MEDICINE,
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