New Views on Neutering
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By Ruth Marrion, DVM
Everyone seems to have an opinion when it comes to neutering dogs. Some opinions are based on fact while others could not be farther from the truth. How many times have you heard pet owners say, "I don't want to spay my bitch because she'll become fat and lazy," "I want her to have one litter before she's spayed because that will improve her personality," or "I don't need to spay (or castrate) my dog because there aren't other dogs around"? Breeders should have rational, factual arguments ready at their fingertips to respond to these types of misguided statements.
Yet despite the fact that people have been neutering* animals since ancient times (writings that discuss canine castration date back as far as 284 BC!), information on the physiological and behavioral effects of neutering has been sparse until recent years. With little scientific data available on the subject, misinformation regarding neutering has been freely disseminated.
This article will discuss some recent scientific studies regarding the physical and behavioral effects of neutering dogs, and explore the concept of early neutering—that is, prior to five to seven months of age. Early neutering was developed to help alleviate the pet overpopulation problem, and may prove to be of further benefit to dog breeders.
*Neutering is a term applicable to an animal of either sex that has had both ovaries or testes removed. This includes dogs who have undergone an ovariohysterectomy (removal of the ovaries and uterus), ovariectomy (removal of the ovaries alone) or orchieclomy (removal of the testes). Unneutered animals are referred to as being sexually intact
Behavioral Effects of Neutering
The estrous cycle of the intact bitch is divided into several stages. The first stage of the cycle is proestrus, in which the bitch is attractive to males but is not receptive to mating. This is followed by estrus (derived from the Greek meaning "mad desire"), in which the bitch is receptive to dogs. The onset of the next stage, diestrus, is defined as the first day after an estrus period when a bitch will no longer accept a dog.
The female hormones estrogen and progesterone, which are produced by the ovary, control the estrous cycle. Estrogen promotes the bitch's desire to mate (behavioral estrus), stimulates growth of the uterus and mammary gland, and sensitizes the uterine muscle to oxytocin, a hormone, during estrus and whelping. Progesterone enhances the effect of estrogens in causing behavioral estrus, and acts in concert with estrogens to promote uterine and mammary growth.
Removal of both ovaries also removes the source of estrogen and progesterone, thus resulting in the abolition of estrous cycles. Since these hormones are responsible for sexual activity, bilateral ovariectomy almost always results in cessation of copulatory behavior for the bitch. The reason that copulatory behavior is not always abolished is not completely clear, but mounting behavior in females has been found not to depend on the presence of estrogen. For example, my Sheltie bitch was spayed as a puppy and at four years of age, she still engages in mounting activity during play with her neutered brother.
Lots of people believe that inactivity and weight gain follow ovariohyslerectomy in the bitch. These changes, however, are difficult to distinguish from changes due to normal maturation. Recent studies have tried to uncover the truth about these supposed effects of spaying.
One report on gonadectomy (removal of the ovaries or testes) in immature dogs' determined that neutered dogs were actually more active than sexually intact dogs. Gonadectomy was found to neither affect food intake nor weight gain. But another group of researchers, comparing food intake in sexually intact and neutered Beagle bitches fed ad libitum, concluded that neutered bitches ate much more than their sexually intact counterparts.
In yet another study5, activity level and weight fluctuations in spayed bitches were compared to those of intact females. The spayed bitches did not gain weight on a diet of a fixed amount of commercial dog food. No data on the effect of orchiectomy on food intake and weight gain in male dogs, other than the study on immature dogs, has been published to date.
The bottom line is that the available scientific evidence about whether neutering influences weight gain and activity in dogs shows that the question is, as yet, unresolved. In other words, it's too early for breeders to jump to either conclusion and therefore, one can't assume the worst.
Eliminating undesirable behavior is often cited as a reason for neutering male animals. Behavior patterns that are altered by neutering are generally male-specific actions such as urine marking, mounting, and intermale aggression. These three types of behaviors, in fact, have been shown to be markedly reduced or eliminated in 50 to 60 percent of dogs as a result of neutering. Behavior patterns common to both males and females, such as watchdog barking, playfulness and attention seeking, are not affected by neutering. No basic personality or behavior changes occur as a result of neutering, with the exception that undesirable male behaviors may be reduced or eliminated.
It is interesting to note that the age at which an animal is neutered does not affect the likelihood that neutering will have an impact on a particular behavior. The chance that neutering will prevent an objectionable male behavior in a pre-pubertal animal is approximately equal to the likelihood that the same behavior will be abolished by neutering an adult animal2.
Experience, on the other hand, does appear to play some role in determining how quickly an undesirable behavior ceases to exist. Copulatory behavior in experienced male dogs may not end completely for months to years following castration. Residual testosterone is not a contributing factor for persistent male-specific behavior patterns, since the hormone is so rapidly metabolized by the body that it is virtually undelectable eight hours following castration.
Finally, many pet owners nurture the belief that bitches become more even-tempered if they produce one litter before being spayed. Neither clinical observations nor animal behavior research bear this out. True, a bitch's behavior will change temporarily as a result of the hormonal changes during pregnancy and lactation, but these effects are transient—not permanent, as some believe.
But if the owners of a bitch manage to convince themselves that her behavior will change as a result of whelping, their way of dealing with the bitch may change, and thereby influence the bitch's ensuing behavior. This is known as the placebo effect2.
There are other circumstances where an owner's expectations and resulting behavior can influence a dog. The placebo effect also plays a role, for instance, when people anticipate certain changes to take place following neutering— weight gain, for example, or decreased activity. Without realizing the implications of their actions, many owners will actually start to feed the neutered animal more food and place fewer physical demands on it. The result: an overweight, sedentary (neutered) animal. Just what owners expected!
The specialized training of behavioral scientists helps them differentiate between various influences on an animal's behavior. Data from their controlled studies are therefore generally more valuable than observations made by casual observers on a limited number of animals.