The Effects of Spaying and Neutering on Canine Behavior
Based on section from Aggressive Behavior in Dogs by James O’Heare
© 2006 James O’Heare. All rights reserved
Spaying and neutering is an often suggested remedy for various behavior problems. This article will be a review of the effects of spaying and neutering on behavior.
Neutering (Gonadectomy) the male dog removes the source of circulating testosterone by removing the testicles, which is presumed to be the major influence on observed changes in behavior following gonadectomy.
Testosterone affects the male dog’s brain intensively at two points in their development. The first is probably prenatally (Hart and Eckstein, 1997) and the second is during sexual maturity. In the uterus, testosterone can diffuse through the amniotic membrane and through uterine blood flow. Once it reaches the male dog’s brain, it brings about gender-specific structural changes that then relate to later development of sex-typical behaviors. Remember that these structures start out female and develop into male structures. These changes masculinize the male brain structure. Prior to sexual maturity, male dogs display male-typical behaviors. During the second significant surge of testosterone in the sexual adolescence period of development, increasing testosterone levels continue to act on these already established anatomical changes to again increase the frequency and magnitude of male sexually dimorphic behaviors. “Testosterone titers start to rise by the time the male pup reaches 4 to 5 months, where after testosterone levels reach a maximum at 10 months of age and then fall to adult male levels by 18 months of age.” (Dunbar, 1999, p. 68) The fact that the dog experiences two significant surges of testosterone, one of which has significant effects on the anatomy of the brain prior to gonadectomy, it is not surprising that gonadectomy does not have total control over sexually dimorphic behaviors.
Ben and Hart at the University of California carried out one of the most extensive surveys on the effects of gonadectomy on dogs, finding that at least in intermale aggression, aggression was reduced by neutering in 60% of cases with rapid reduction in 25%, and gradual reduction in 35% (Fogle, 1990, p. 53). Neilson, Eckstein, and Hart, (1997) found that approximately 25% of adult dogs that were aggressive toward humans or other dogs in the household can be expected to have a 50 to 90% level of improvement after gonadectomy. A 50 - 90% level of improvement can likewise be observed in 10 to 15% of dogs that are aggressive toward unfamiliar people or human territorial intruders after gonadectomy. Neilson et al. also found that neither the age at which the gonadectomy was performed or the duration the problem behavior existed for affected the behavior after gonadectomy. Hart and Eckstein (1997) performed a review of the research and literature on the effects of gonadal hormones on objectionable behavior. They relay that gonadectomy affects sexually dimorphic behaviors and that aggression toward other dogs and “dominance over owner” are particularly sexually dimorphic. They point out that much previous research has largely been based on guardian survey studies and has not experimentally controlled for the placebo effect in that guardians may either instate some form of changes that constitute behavior modification or they may imagine changes that in fact did not take place or did not take place to the extent they believed they did. Although this is a serious lacking in the validity of the studies these same affects can be expected in real life gonadectomies performed as part of behavior management plan. To the extent that the guardian makes changes in their behavior or the environment that result in decreases in aggressive behaviors simply as a result of having the gonadectomy performed these same results can be expected in behavioral cases. A large scale German study by Heidenberger and Unshelm (1990) found very similar results to those described above.
Testosterone tends to promote greater reactivity in dogs. They trigger a little quicker to aversive stimuli and respond a bit more intensely and for slightly longer duration. Affecting the magnitude of aggressive behavior could be particularly helpful in many cases.
Some general statements and recommendations can be formed from these studies and notions.
· Neutering cannot be expected to reduce aggressive behavior in all dogs
· Neutering will not always completely eliminate aggressive behaviors
· When the neutering is carried out cannot be expected to influence the rate or magnitude of changes in behaviors
· How long the problem behavior has existed does not tend to affect the level or trend of change in behavior after neutering
· If an intact dog demonstrates aggressive behavior neutering should be considered as an adjunct to other behavior modification practices
· Early neutering is probably not helpful at preventing aggression and may pose certain medical risks.
Spaying (ovariohysterectomy) is the surgical removal of the ovaries and uterus, the source of estrogen and progesterone in female dogs. Estrogen and progesterone levels ebb and wane in cycles. The most significant influence cycling fluctuations in estrogen and progesterones have on female dog behavior is pregnancy related behaviors (female sexually dimorphic behaviors). “While estrogen increases in the dog’s body for a short length of time, progesterone remains in circulation, influencing the brain for two months after each estrous and can have a dramatic effect on canine behavior. The most common behaviors are those associated with pregnancy, nest building, guarding possessions and milk production.” (Fogle, 1990, p. 54)
The most notable problem arises when the dog guards items maternally. Other problems can involve irritability, conflict with other dogs and energy reduction. Possessive guarding in intact females that occurs in cycles is usually a hormonal guarding.
With a lack of testosterone to masculinize the brain in utero, female dogs maintain their female brain structure. Both males and females start with the basic brain organization for male and female behaviors. The phenotype results from the probability or frequency with which the feminine or masculine system is activated in very early development.
Sexual dimorphism is a matter of degree rather than an all or nothing phenomenon. Most male dogs behave typically male and most female dogs behave typically female in terms of sexually dimorphic behaviors. Some male dogs display fewer or lower magnitude male sexually dimorphic behaviors and in some cases display some female sexually dimorphic behaviors. Likewise, some female dogs display fewer or lower magnitude female sexually dimorphic behaviors and in some cases display some male sexually dimorphic behaviors. Think of it as a continuum. One explanation for this is the basic similarity and integration of behavioral systems of males and females of the species. Another explanation is that the masculinizing effects of testosterone are a matter of degree rather than a zero-sum trigger and that some individuals in the uterus are exposed to greater or lesser amounts of testosterone.
It has been found (O’Farrell and Peachey, 1990; and also discussed in Hart and Eckstein, 1997) that the only two behaviors affected by spaying of female dogs was “aggressive dominance” toward guardians and indiscriminate eating. In this case, the aggressive behavior increased after spaying. This effect was only noted in female dogs ovariohysterectomized before 12 months of age, and that already demonstrated aggression. Female dogs ovariohysteretomized after 12 months of age presented no risk of increased aggression. Hart and Eckstein (1997) point out that female dogs are in a progestational state for two months following an estrus period and spaying them during that time creates a sudden removal of the source of progestins (which tend to have a calming influence on animals). It is proposed that this removal of progesterone may promote irritability or aggression in some individuals.
Another piece of this puzzle may involve androgenization of fetal female dogs. It is suggested that either or both of two mechanisms may lead to a slight masculinization of female brains in untero. If a female is positioned between two males in utero, their brain may be masculinized by diffusion of testosterone through the amniotic membrane. The other mechanism involves caudally (closest to the tail of the animal) positioned males androgenizing rostrally (closest to the head of the animal) positioned females in utero through the fetal blood supply. For a good discussion of this, see Hart and Eckstein (1997).
In a study by Kim, Yeon, Houpt, Lee, Chang and Lee (2005, in press) it was found that female German Shepherd Dogs spayed between five and 10 months were significantly more reactive than an intact group. The intact group was not exposed to a sham operation so even though the measures were taken well after the surgery it is possible that the results are due to the surgical procedure rather than the absence of ovaries and uterus. It is also possible that the results are only reasonably generalizable to German Shepherd Dogs. This study does suggest though that spaying may cause more reactivity in dogs. Replication will be important.
Some statements and recommendations can be derived from the above:
· Females should not be spayed within two months after their estrus period to avoid sudden contrast between the presence and absence of progesterone
· If a female demonstrates this consistent “dominance” related aggression pattern prior to spaying and prior to 12 months of age the risk of increased aggressive behavior must be balances against the inconvenience of an intact female dog and potential health detriments of remaining intact. Spaying can simply be delayed until behavior modification has achieved progress
· Early spaying is likely not helpful at preventing aggression and may pose certain medical risks.
Dunbar, I. (1999). An Owner's Huide to a Healthy Happy Pet Dog Behavior. New York: Howell Book House.
Fogle, B. (1990). The Dog's Mind. New York: Howell Book House.
Hart, B. L., & Eckstein, R. A. (1997). The role of gonadal hormones in the occurrence of objectionable behaviours in dogs and cats. Applied Animal Behaviour Science, 52, 331-344.
Heidenberger, E., & Unshelm, J. (1990). Changes of behaviour in dogs after castration. Tierarztliche Praxis, 13(1): 69-75.
Kim H. H., Yeon S. C., Houpt K. A., Lee H. C., Chang H. H., and Lee H. J. (2005). Acoustic feature of barks of ovariohysterectomized and intact German Shepherd bitches. J Vet Med Sci. 67(3):281-5.
Neilson, J. C., Eckstein, R. A., & Hart, B. L. (1997). Effects of castration on problem behaviors in male dogs with reference to age and duration of behavior. Journal of the American Veterinary Medical Association, 211(2), 180-182.
O'Farrell, V., & Peachey, E. (1990). Behavioural effects of ovariohysterectomy on bitches. Journal of Small Animal Practice, 31, 595-598.