Desexing Dogs: A Review of the Current Literature

Abstract

Background: Desexing dogs is promoted for population control, preventative healthcare, and behavior modification. Common methods are orchiectomy and ovariectomy/ovariohysterectomy. GnRH superagonist implants are available in some areas. Alternative methods like vasectomy and salpingectomy/hysterectomy are uncommon. The terminology used to describe desexing is inconsistent and contradictory, showing a need for the adaption of standardized terminology. Population Control: Surprisingly, empirical studies show no effects of desexing on population control in companion and shelter dogs despite desexing being consistently recommended in the literature. There is evidence for a population control effect in free-roaming dogs, where desexing also has benefits on zoonotic disease and bite risk. Population control in free-roaming dogs is mostly correlated with female, not male desexing. Health and Lifespan: Desexing affects numerous disease risks, but studies commonly neglect age at diagnosis and overall lifespan, age being by far the most important risk factor for most diseases. We argue that lifespan is a more important outcome than ultimate cause of death. A beneficial effect of desexing on lifespan is consistently demonstrated in females, while evidence for a beneficial effect in males is inconsistent. Studies are likely biased in desexing being a proxy for better care and desexed dogs having already lived to the age of desexing. Desexing reduces or eliminates common life-limiting diseases of the female reproductive system such as pyometra and mammary tumors, while no analogous effect exists in males. Disease risks increases across sexes and breeds include cruciate ligament rupture, various cancers, and obesity. Urinary incontinence risk is increased in females only. Various other disease risk changes show considerable variability between breeds and sexes. Behavioral Effects: Desexed males show reduced libido, roaming, conspecific mounting, and urinary marking frequency, as well as reduced male dog-directed aggression in a majority of males desexed for behavioral reasons. There is a detrimental effect on the risk and progression of age-related cognitive dysfunction. Desexed dogs may be less likely to cause bite injuries across sexes. The evidence for other effects such as human-directed aggression, human or object mounting, resource guarding, or shyness and anxiety is inconsistent and contradictory. There are few studies specific to females or individual breeds. Conclusions: The evidence for a beneficial effect of desexing is stronger in female than in male dogs; however, there is significant variation between breeds and sexes, and more research is needed to further elucidate these differences and to arrive at individualized evidence-based recommendations for clinical practice.

Active and social life is associated with lower non-social fearfulness in pet dogs

“…Intact females were more fearful in novel situations than intact males, but no difference was found between neutered males and females. However, a recent review 46 concluded that the effect of sterilisation on fearful behaviour is inconsistent and even contradictory. Thus, our results should be interpreted with caution.…”

Lifespan of companion dogs seen in three independent primary care veterinary clinics in the United States

“…It is generally agreed that lifespan in dogs is inversely correlated with body weight [12,31,32], even though considerable variation in life expectancy exists between different breeds within the same body size class [9,18,20,33,34]. It is also widely accepted that gonadectomized female dogs generally live longer than intact females of the same size [10,17,18,20,35]; however, the evidence is less clear regarding the effects of gonadectomy on lifespan in males [11,35]. In addition, several studies have looked at the effects of gonadectomy without differentiating between sexes, which may result in the strong effect of female gonadectomy overwhelming the possible lack of such an effect in males, and making it appear that an overall effect exists [34,35].…”

“…It is also widely accepted that gonadectomized female dogs generally live longer than intact females of the same size [10,17,18,20,35]; however, the evidence is less clear regarding the effects of gonadectomy on lifespan in males [11,35]. In addition, several studies have looked at the effects of gonadectomy without differentiating between sexes, which may result in the strong effect of female gonadectomy overwhelming the possible lack of such an effect in males, and making it appear that an overall effect exists [34,35]. Furthermore, the influence of age at gonadectomy has not thus far been studied in any large population comprising multiple breeds.…”

Self-reports of Dutch dog owners on received professional advice, their opinions on castration and behavioural reasons for castrating male dogs

“…Carefully weighed decisions on castrating dogs are necessary as the scientific information on the effects of desexing dogs, males in particular, is complex and to date incomplete. Strong causal evidence on castration affecting a broad range of behaviour is lacking [5,6]. Castration of the male dog has been related to reduced inter-male aggression, marking and roaming [7,8], indicating possible benefits of the procedure.…”

“…This again after excluding the dogs that were desexed for reasons of correcting unwanted behaviour and when considering multiple aggression affecting factors [22]. With this complexity in findings on desexing and behaviour and the lack of causal evidence [5,6], how dog owners are advised becomes of interest. This as there is reason to assume that desexing facilitates aggression in a subset of dogs.…”