Birth Control Alternatives
TEXTBOOK OF VETERINARY INTERNAL MEDICINE
Client Information Series; written by Dr Autumn P. Davidson
Neutering, ovariohysterectomy (spaying) of females or castration of males, remains the most effective, least expensive, safest, and permanent method of birth control for pets.
The procedures are well tolerated by dogs and cats and are routinely performed in most veterinary hospitals, and both dogs and cats can have the surgery as young as 6 to 8 weeks of age.
The only valid reason to avoid neutering as a birth control method is that the pet has value as a breeding animal.
A valuable breeding animal has desirable physical and behavioral traits for its (pure) breed. This animal should have undergone appropriate testing and found not to have evidence of any known genetic defects. In addition, the owner of that pet must be willing and able to take responsibility for managing breeding, whelping or queening, weaning, socializing, and placing the offspring produced.
Breeding dogs and cats is not a financially rewarding undertaking-much the opposite!
Financial setbacks are common, raising puppies and kittens can be quite time consuming, and finding desirable homes for the offspring is a major responsibility.
The pet overpopulation problem is a gigantic and serious reality in the United States that underscores the need for responsible breeding.
Breeding animals should be neutered for health reasons when their reproductive careers are com-plete.
Neutered animals have the same capacity to perform as hunting, herding, and guard animals.
Breast cancer is at least as common in dogs and cats as in people, and spaying a female before her first "heat" virtually eliminates risk of breast cancer in dogs and cats.
Spaying between the first and second cycles dramatically decreases the risk of breast cancer.
Obviously, spaying also eliminates risk of diseases of the ovaries or uterus, which are relatively common.
Prostate and testicular diseases are also common, and neutering of males decreases the risk of these problems as well.
Neutered animals should be fed approximately 25 per cent fewer calories to prevent obesity; otherwise, their physique remains normal.
Urinary incontinence occasionally occurs in spayed female dogs. This condition is treatable.
Alternatives to neutering for temporary birth control in pets are few.
Most products available in the United States are not licensed for use in pets or are not recommended for pets intended for breeding.
None have current application to the male.
Birth control in females is accomplished by preventing estrous cycles or interrupting pregnancy establishment.
Estrous cycles can be prevented in bitches or queens by appropriate administration of commercially available veterinary progestin or testosterone compounds.
Progestin compounds work to prevent estrous cycles by keeping the female in a "pregnant-like" condition.
Unfortunately, the administration of progesterone to an intact (unspayed) bitch or queen can cause uterine wall disease, leading to the later development of a severe and potentially life-threatening uterine infection called "pyometra" or infertility.
Progesterone medications can also cause or contribute to the development of serious diseases (diabetes, growth hormone disorders) and anatomic problems (mammary masses, gallbladder disorders).
Therefore, we do not recommend the use of progestogens to prevent estrous cycles. Testosterone-like compounds prevent estrous cycles in bitches by keeping the female in an anestrus-like (no ovarian activity) condition.
Behavioral side effects (aggression), tearing of the eyes, malodorous skin, liver problems, and sub-fertility during subsequent estrous cycles are common consequences of the use of testosterone compounds. Clearly, these are not ideal compounds for use in valuable breeding animals.
Methods for preventing estrous cycles by administering synthetic hormones with fewer side effects or immunizing the animal against egg membranes or endogenous hormones have not been perfected to the point where they are commercially available.
Methods for preventing pregnancy by interfering with egg travel in the fallopian tubes or embryo implantation in the uterus with estrogen compounds are not recommended because of their potential for causing life- threatening bone marrow suppression (the bone marrow is the sole source of red and white blood cells and cells that help clotting, called platelets).
Estrogens may also promote later development of pyometra, clearly undesirable in an animal intended for breeding. Application of newer human birth control agents, such as carbergoline and mifepristone, in pets is limited by availability in the United States, but these agents have the best promise for providing effective birth control with minimal side effects.
The best current nonpermanent method for preventing pregnancy in the bitch or queen is simply to prevent breeding (copulation) by confining the individual indoors, away from intact (un-neutered) males.
Bitches should be let into an enclosed yard only with direct supervision or on leash for the entire time when copulation could occur. This could be as long as 3 weeks. A veterinarian can determine when the bitch's cycle is complete by performing vaginal cytology.
Queens must be kept isolated from toms during their entire period of receptivity, as they ovulate after copulation.
More Articles About Other Methods of Neutering and Spaying
Currently, researchers are trying to develop injectible forms of immunocontraceptives, or contraceptive vaccines, that will prevent pregnancy. In a few years, researchers hope to have a sterilization vaccine that will be safe and reliable, not to mention FDA-approved.
Several different companies and universities are working on their own variations of this concept; all are still in the research or development stages. Some organizations are working on a one-time, permanent vaccine, while others are looking into a method that would result in temporary infertility. Some vaccinations would be for females, others for males; some are concentrating on dogs, while others are working on a feline vaccine.
A number of these injections use porcine zona pellucida (PZP) which is the membrane surrounding female pig eggs. All female mammals have a similar coating on their eggs, which allows the sperm to fertilize the eggs. "When you inject it into the animal, the animal produces antibodies against the PZP," explained Irwin Liu, a professor in the University of California at Davis College of Veterinary Medicine's Department of Population Health and Reproduction. The PZP is not exactly the same as the animal's own egg membrane, but has common properties and so the antibodies bind to the egg, blocking any sperm.
Dr. Liu is currently working on a vaccine that will chemically sterilize dogs. He estimates it will be approximately five to 10 years until the vaccine is ready for commercial use. Right now it is being tested on dogs.
The vaccine is a variation of another PZP vaccine he has already developed for female horses. This injection has been used successfully in wild horses by the U.S. Bureau of Land Management.
There hasn't been as much research on sterilizing cats, he said, mostly due to a lack of interest. For some reason, he said it seems that more money is available for canine research. Nevertheless, he hopes the vaccine will eventually be available in a feline form as well. The shot would be great for controlling both feral cat and dog populations, he said. It might even be good for wild rats and other pests, he added.
Another vaccine designed for female cats is being developed by microbiologist Dr. Stephen Boyle and theriogenologist Dr. Beverly Purswell at the Virginia-Maryland Regional College of Veterinary Medicine. This oral vaccine does use PZP but is delivered in genetically engineered bacteria that is placed in a food bait left out for feral cats.
Currently, they are trying to make the vaccine specialized to cats so that any other animal that ate the bait would not be unintentionally sterilized.
Neutersol (Note: now approved but not yet available)
Neutersol is a shot that is injected into the scrotum of male dogs and ceases sperm production. It. is not yet approved, but it could be useful to control overpopulation of dogs.
Even when and if permanent sterilization alternatives become available to the public, surgery may still be the best choice, said Dr. Deborah Beck-Ross, a small animal veterinarian in West Grove, Penn, who has been following these recent developments. "There are two reasons to perform ovariohysterectomies and castrations in dogs and cats," she said. "Obviously the most commonly known reason is to prevent unwanted births. Even more importantly in my mind are the health benefits the pets get as a result of the neutering."
Female dogs and cats that are spayed benefit from the prevention of life-threatening uterine infections, called pyometras, endometriosis, and uterine and ovarian cancer, as well as a reduced risk of mammary cancer. Neutered male dogs and cats can benefit from prevention of testicular infections, known as orchitis, testicular cancer, prevention or dramatic reduction of anal cancer, reduction in incidence of prostatic infections, and reduction in incidence of prostatic cancer.
"It would not benefit the pet at all," Dr. Beck-Ross said, "it would just reduce the pet population by decreasing offspring and increasing disease in the adult pet population and shortening their life-span."