4.8.4 Effects of Gonadectomy on the Behavior of Dogs
The behavior of gonadectomized male dogs is similar to that of an anestrus female. Early studies indicated that castration of male dogs results in a reduction of sexually dimorphic behaviors, such as mounting, urine marking, roaming, and aggression directed toward other intact male dogs (Hopkins et al. 1976; Neilson et al. 1997). However, it should be noted that in these two studies the behaviors were only reduced in some dogs; none of the objectionable behaviors were completely eliminated. A more recent survey that included more than 9,000 dogs found that urine marking was the only behavior less likely to occur in the castrated dog (McGreevy et al. 2018). This study also found that behaviors relating to fear and aggression were less likely to occur the longer the dog remained intact prior to castration (McGreevy et al. 2018). Several other studies have demonstrated that there is no difference in aggression after gonadectomy (Maarschalkerweerd et al.1997), while other studies suggest that aggression in males may increase after gonadectomy (Guy et al. 2001; Spain et al. 2004; Reisner et al. 2005).
Conflicting results have also been found when attempting to determine if castration prior to six months of age has any effect on the development of certain behavioral problems. One study found male puppies castrated prior to five‐and‐a‐half months of age demonstrated increased aggression toward family members and were more likely to bark at visitors (Spain et al. 2004). However, in another study comparing puppies castrated prior to 24 weeks of age, no increased incidence of behavior problems was identified (Howe et al. 2001). Vizslas castrated prior to six months of age were found to have an increase in behaviors related to fear and anxiety (Zink et al. 2016).
A minimal amount of research has been performed examining the effects of gonadectomy on female dogs. One study (O’Farrell and Peachey 1990) suggested that if female dogs were already showing some aggression and gonadectomy was performed prior to one year of age, the risk of aggression increased after surgery. Other females in the study who were gonadectomized after one year of age did not show an increased likelihood of aggression. In another, more recent study that included 8,981 dogs who were gonadectomized prior to 10 years of age, fearful and aggressive behaviors were associated with a decreased lifetime exposure to gonadal hormones. In other words, the longer female dogs were left intact, the lower the incidence of several unwanted behaviors (Starling et al. 2019).
A 2018 survey study that included more than 13,000 dogs of both sexes found no evidence to suggest that gonadectomy at any age alters aggressive behavior directed toward people or dogs, but dogs that were gonadectomized prior to 12 months of age had a significant increase in the odds of demonstrating aggression toward strangers (Farhoody et al. 2018). The apparently conflicting nature of these data demonstrates the complex and multifactorial elements surrounding the development of behavior. A variety of different confounding factors may have influenced the results of the data in these studies, and much more prospective research is needed on this issue. Until we have that, all we can say is that gonadectomy may help to decrease behaviors that are strongly influenced by gonadal hormones.
An important concern not adequately addressed in any of the aforementioned studies is the possible role that a traumatic experience may have on the development of the aggressive behaviors that are described in some gonadectomized dogs. If dogs have a surgical procedure performed prior to 6 or 12 months of age (the most common time frames for dogs in the United States to be neutered), the fact that the surgery may be performed during a sensitive period of development needs to be taken into consideration. Dogs who experience a traumatic event, such as a frightening and/or painful experience in the veterinary hospital or shelter during the sensitive period, may be at a greater risk for developing fear‐ or anxiety‐related problems. This may artificially bias studies to suggest that it is the gonadectomy that leads to aggression, rather than the actual experience in the clinic or shelter. It is critical not to ignore the role that early experience plays in the development of behavior problems in dogs and cats.
When possible, special consideration should be given to intact dogs who enter the shelter already showing high levels of fear and anxiety. This can be challenging since the shelter is inherently a scary place for many dogs, and postponing surgery is impractical. To prevent the exacerbation of fear as much as possible, extra attention must be given to relieving their anxiety with medication prior to, during, and immediately after neuter surgery. Increased attention to low‐stress handling and teaching staff to read canine body language, both strategies suggested by the Fear Free™ initiative, have the potential to decrease the likelihood of a traumatic experience associated with early gonadectomy that could profoundly affect the future behavior of companion animals. See Chapters 8 and 14 for more information about low‐stress handling for dogs and cats.
All that we can really conclude at this time from the conflicting data regarding gonadectomy and the “ideal” age for gonadectomy is that there are, and always will be, certain risks and benefits to performing gonadectomy on any animal. Due to the variety of different methods used in studies thus far, the varying ways in which “early gonadectomy” is defined, and the differing definitions or descriptions used to identify behaviors in assorted studies, it is difficult to even compare data from one study to the next. In addition, due to the varying populations used for the studies, we cannot automatically assume that all of the data can be extrapolated and applied equally to all other populations of dogs. Due to the important role that genetics and environment can play in so many of the discussed conditions, one can never assume that a population of dogs in one country will respond to any intervention in an identical way as the population of dogs in another country. The same can be said of the few breed‐specific studies in the literature. The results among the studied breeds vary, so it is to be expected that other breeds as yet unstudied will reveal different findings. What we do know is that gonadectomy appears to be associated with a longer lifespan in dogs (Reichler 2009; Houlihan 2017), and more intact animals are returned to the shelter than neutered animals (Patronek et al. 1996; New et al. 2000), which has a more immediate impact on long‐term health due to premature euthanasia. The benefit of early sterilization for animals in shelters and humane societies likely outweighs all of the other risks.
4.9 Behavior and/or Medical Conditions Seen in Intact versus Neutered Cats
4.9.1 Female Feline
The normal reproductive cycle of the queen is very different from the bitch. Unlike the bitch, the queen is an induced or reflex ovulator and is seasonally polyestrous, having more than one estrous cycle during the breeding season (Houpt 2005). Queens only ovulate in response to cervical stimulation. The queen’s cycle consists of four phases that include proestrus, estrus, metestrus (diestrus and interestrus), and anestrus (Griffin 2001). Metestrus is the time between two estrus cycles if breeding has not occurred. If breeding does not occur, the queen may return to proestrus with the next follicular wave, which is typically between one to three weeks but has been reported from three days to seven weeks in some cases (Feldman and Nelson 1996; Root et al. 1995). Anestrus is the time between breeding seasons. The age kittens begin to cycle is dependent on when they were born relative to the breeding season, typically anywhere from 6 to 10 months.
The female will undergo several behavioral changes during the estrus cycle. During the proestrus stage, the queen is often very affectionate, rubbing her head on any object, both animate and inanimate, and seeming friendlier, although some females will not show any signs during proestrus. This behavior is consistent with scent marking to notify other cats that there is a female coming into estrus. There may be a slight increase in vocalization and rolling, as well as stretching and lying in lateral recumbency while kneading with the paws. Toms may show some interest in the queen at this time, although she will not be interested in them and may act very aggressively: slapping, hissing, chasing, and/or biting the tom. The vulva may be slightly enlarged, but this generally goes unnoticed because of its anatomical location and relatively small size to begin