Birth Control Alternatives (In Pets)

 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 pup-pies 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 complete. 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 pre-venting 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.

The above is general veterinary information. Do not begin any course of treatment without consulting your regular veterinarian. All animals should be examined at least once every 12 months.

About the author:

From the Textbook of Veterinary Internal Information: Client Information Series. Copyright © 2000 by W.B. Saunders Company. All rights reserved.

Linda Mar Veterinary Hospital and its cat-only affiliate, Coastal Cat Clinic, are small animal practices located in Pacifica, California.

 Autumn P. Davidson, DVM