To spay or not to spay: the nurse's role in owner education

Mammary tumours

The incidence of canine mammary tumours is difficult to establish due to wide variation in the studies that have been done, but a review of a census of dogs and a canine cancer registry in Norway, where neutering is illegal except on medical grounds, found an incidence in female dogs as high as 53.3% for malignant tumours, although a breed variation was noted (Moe, 2001). A study of data from insurance claims in Sweden found an incidence of 13% at 10 years of age. This study did not record neuter status but routine neutering is not common in Sweden. It also had no data for dogs after 10 years of age, which may explain the variation (Egenvall et al, 2002). A further UK study found much lower incidence (Dobson, 2002), but again was only looking at claims submitted to an insurance company for different cancer types. The number of insured animals in the UK that are neutered will differ somewhat to the general dog population so may not be a true representation. When evaluating studies looking at the incidence of mammary tumours it should be remembered many studies are based on figures from insurance claims or pathology labs. There will be a proportion of the dog owning public who do not present their pets for treatment, or who opt for immediate euthanasia so these would not be accounted for. It is believed that tumours which begin as benign can transform into malignancies (Sorenmo et al, 2009) with the potential for metastatic disease leading to death of the patient (Figure 1) (Sleeckx et al, 2011).

Ovariohysterectomy has been proven to have a preventative effect against cancers of the mammary tissue, as it is believed oestrogen is implicated in their formation (Sleeckx et al, 2011). Results of tissues presented for laboratory analysis showed 88% were from intact bitches (Bronden et al, 2007), another similar study showed 76% (92 of 121) (Sontas et al, 2009a). The earlier surgery is performed the better the preventative effect, the risk of developing a mammary tumour is reduced to 0.5% if done prior to the first oestrus, but after 2 cycles or by 2.5 years of age, this rises to 26% (Sleeckx et al, 2011). The apparent advantage of spaying to prevent mammary tumours is widely documented (Root Kustritz, 2012), but it is important that clients are given the correct information and are not led to believe spaying later in life will prevent these types of tumour.

Pseudocyesis

Pseudocyesis is a condition that occurs in entire bitches usually 6 to 12 weeks after oestrus. Not all dogs will be presented for treatment and many owners accept it as ‘normal’, unless clinical signs are severe. Changes seen include enlargement of the mammary glands with lactation, weight gain and often distressing behavioural changes (Gobello et al, 2001a). The incidence is estimated to be 50–75% of entire bitches, although the severity of signs varies greatly (Gobello et al, 2001b). There is no way of preventing pseudocyesis other than spaying, although the timing of surgery is important to prevent inducing or prolonging clinical signs (Warnes, 2014).

Pyometra

A case-controlled study looking at medical records of animals being presented for treatment of pyometra showed just over 17% of intact bitches affected, with an average age of 7 years; eight breeds were identified as having an increased incidence (Igna et al, 2009). This correlates with a study of laboratory beagles showing a similar incidence, with a slightly higher average age of 9 years (Fukuda, 2001). There is a suggestion that previous pregnancies appear to have some protective effect against pyometra, but this study only looked at 87 dogs from five different breeds (Hagman et al, 2011). This is supported by results of the study by Fukuda (2001) on laboratory beagles, but again this only looked at one breed therefore further research would need to be done to confirm these results using more cases and different breeds. The traditional treatment for pyometra is to perform a complete ovariohysterectomy (Figure 2), although the bitch may need to be medically stabilised first. Medical management may be attempted, but owners should be warned the bitch's fertility rate may be reduced, and there is a risk of the pyometra recurring (Smith, 2006).

Reproductive cancers

Canine ovarian cancers are uncommon in bitches (Sforna et al, 2003), as are cancers of the uterus, vulva and vagina (Van Goethem et al, 2006). Vaginal and vulvar tumours are much more common in entire bitches than spayed bitches as it is believed they are influenced by sex hormones (Sontas et al, 2009b). Spaying should reduce the risk of these types of tumour, and it will eliminate the risk of ovarian and uterine cancers (Van Goethem et al, 2006) as long as these are removed in their entirety.

Population control

Spaying bitches is promoted as being of major benefit for control of the dog population in the UK. While this may have obvious benefits for multi-pet households and in owners attending canine events, or going for off-lead walks, neutering of dogs is not essential for control of the canine population. Neutering is extremely uncommon in Northern European countries and yet countries such as Sweden have no stray dog problems due to very strict legislation and control of breeding. Owner education means accidental litters do not occur, and they view the surgery as an unnecessary risk to a healthy dog. Their example shows neutering should not be viewed as the main method of population control, education and owner responsibility is the key (Tasker, 2007). Alternative options are available to control reproduction in multi-dog situations, such as the male dog hormonal implant (Curtis, 2014).

Urinary incontinence

Urinary incontinence, specifically urethral sphincter mechanism incompetence (USMI), in entire bitches is estimated to be as low as 1%, but in spayed bitches it is between 5% and 20%. Signs of incontinence may be immediate post surgery, or in some cases delayed up to 10 years, mean age at onset is 5 years of age. Although ovariohysterectomy has been proven to play a part in the development of incontinence the exact cause is not known and is believed to be due to multiple factors (Shiel et al, 2008). There is a belief that timing of neutering may be responsible for subsequent development of incontinence. One US study including 1842 bitches showed that bitches spayed prior to 14 weeks of age were more likely to suffer from cystitis and incontinence (Spain et al, 2004), however neutering prior to 14 weeks of age is not commonly carried out in the UK. A study by Thrusfield et al (1998) consisted of questionnaires completed by 233 randomly selected veterinary surgeons and comprising 809 bitches. It looked at the incidence of incontinence related to whether the bitch was spayed prior to, or after the first oestrus, but no significant difference was found. A later study by Stocklin-Gautschi et al (2001), of questionnaires completed by 206 owners of dogs spayed before 7 months of age appeared to show a decrease in incontinence in bitches spayed prior to their first oestrus. The average age of the bitches at the end of the study was 6.5 years, therefore these bitches may go on to develop incontinence later in life. A case-control study carried out in London in 2005–2006 consisted of questionnaires completed by owners of spayed bitches, both continent and incontinent which also supported the theory that spaying prior to first oestrus does not increase risk of urinary incontinence. There seemed to be a higher incidence of incontinence in dogs over 10 kg in weight, and in docked breeds which may be due to atrophy or damage to the muscles (De Bleser et al, 2011). Excessive adhesions formed from the surgical procedure and uterovaginal fistula formation from incorrect placement of the uterine ligature are both iatrogenic causes which may be minimised by careful tissue handling and surgical technique (Bohling, 2008).

Cruciate ligament disease

There have been various studies confirming that rupture of the cranial cruciate ligament is more common in neutered than intact animals (Whitehair et al, 1993; Duval et al, 1999; Slauterbeck, 2004). These case-controlled studies appear unbiased, with data from over 3000 and 10000 dogs in two of the studies. The exact pathogenesis and cause has yet to be identified (Ragetly et al, 2011). The age at the time of neutering (<6 months of age) does appear to affect the tibial plateau angle (TPA) which has been identified as a potential risk factor for cruciate ligament disease (CLD) (Duerr et al, 2007). Further research is needed to establish if there is a definite link between TPA and CLD, and how much of a factor this is (Ragetly et al 2011), or if there are other effects of neutering causing the increase (Root Kustritz, 2012). Other risk factors found to be associated with CLD include breed (Duval et al, 1999), and obesity (Ragetly et al, 2011). A recent study of golden retrievers identified no entire dogs affected by CLD (Torres de la Riva et al, 2013), however entire dogs may have much less freedom in terms of ‘off-lead’ exercise and this was not taken into account. A recent internet-based owner survey indicated that dogs participating in agility activities commonly suffer from ligament injuries, often attributed to interaction with jumps and A-frames (Cullen et al, 2013). More research, with veterinary involvement, would indicate whether CLD is more common in these dogs, who due to their large amount of socialisation with other dogs, are usually neutered (author's opinion).

Hip dysplasia

A review of studies by Root Kustritz (2012) indicated that hip dysplasia may be more common in neutered animals, which agreed with the 2005 findings by Van Hagen, although in this study bodyweight of affected animals was not recorded, only one breed was analysed and the timing of neutering was not recorded therefore these data should be interpreted with caution. A study by Spain et al (2004) examined medical records for over 2000 dogs homed from US shelters that had been neutered prior to rehoming. This identified that being spayed prior to 5.5 months of age was a high risk factor for hip dysplasia, with spaying prior to 1 year of age also increasing the risk; it was believed this may be due to hip joint conformation secondary to increased bone length. Diagnosis was based on medical records obtained from animals' first opinion veterinary practices. Interpretation of hip radiographs may vary greatly between vets (Kapatkin et al, 2002), and misdiagnosis of hindlimb lameness is a common occurrence (Powers et al, 2005). A smaller study consisting of 269 dogs homed from shelters showed no increase in the development of hip dysplasia or other musculoskeletal disease following neutering (Howe et al, 2001). Other factors such as breed or bodyweight were not recorded in these studies and it is not known whether certain breeds are over represented in those homed from shelters. A recent study by Torres de la Riva et al (2013) concluded that hip dysplasia was more common in neutered versus unneutered golden retrievers, however this breed has a predisposition towards hip dysplasia and it may be that those that had been neutered were done so as they were not deemed suitable for breeding due to being from lines with poor hip conformation. Obesity is a known risk factor for hip dysplasia, and there is a known link between neutering and excessive weight gain (Sallander et al, 2006). A cohort study on Labrador retrievers showed the onset of osteoarthritis associated with hip dysplasia was delayed and less severe in the group that was diet restricted (Smith et al, 2006). High impact exercise has been identified as a risk factor for hip dysplasia (Sallander et al, 2006) so further studies should take all risk factors into account.

Osteosarcoma

A case-controlled study with information obtained from a medical database looking at >3000 cases of confirmed osteosarcoma showed the risk of osteosarcoma increased with age, weight (which links to neutering) and height of the dog, with large and giant breeds at greatest risk (Ru et al, 1998). It showed that neutered dogs were twice as likely to have osteosarcoma as entire dogs. However, the age at time of surgery was not recorded therefore the effect of hormones on the bone during growth cannot be evaluated, and the study only included pedigree dogs. A study specifically looking at Rottweiler dogs, which as a breed are known to have a high incidence of osteosarcoma (Figure 3), found that dogs neutered before 1 year of age have an increased risk of developing osteosarcoma during their lifetime (Cooley et al, 2002). This study only looked at one breed known to be at high risk of osteosarcoma therefore further research would need to be done to establish whether this trend is true within other breeds.

Obesity

Obesity is a growing problem in the pet dog population globally (German, 2006), it is estimated that as many as 40% of pet dogs in the UK are classed as obese. Being overweight may lead to or worsen various diseases such as diabetes mellitus, joint disease and cardiorespiratory conditions. There is also evidence that obesity can be a factor in dogs with incontinence, and some dogs regain continence once their ideal bodyweight is achieved (German, 2011).

A study by Jeusette et al (2006) showed that post neutering female beagles required 30% less energy to maintain their ideal bodyweight. This study only looked at four dogs from one breed, and they were kept in a laboratory environment rather than as a pet in a home, so results should be interpreted with caution. Some breeds are more prone to obesity than others (Root Kustritz, 2012), and exercise and feeding regimens may vary in dogs kept in a pet home. A random study of 339 pet dogs in the UK showed that neutered dogs were more likely to be classed as overweight or obese (59% of the neutered dogs surveyed), however other contributing factors were identified such as age of owner, weight of owner and age of the dog (Holmes et al, 2007), therefore the neutering is not the only risk factor. Recent studies suggest the reason for the weight gain post neutering is not due to a decrease in metabolic rate as was previously thought, and is often quoted to owners post neutering, but is due to behavioural changes causing a decrease in activity levels and an increase in food intake (German, 2006), supported by a study reporting an increase in appetite in 150 dogs post spaying (O'Farrell and Peachey, 1990). Weight gain should be controllable with careful management (Root Kustritz, 2012) if the amount of food on offer is controlled, or through the use of foods providing more satiety.

Behaviour

There have been studies indicating that spayed bitches are more likely to be reactive and show aggressive behaviour (Reisner et al, 2005), particularly those spayed before 1 year of age (Kim et al, 2006), and those showing aggression prior to spaying (O'Farrell and Peachey, 1990). Behaviour is influenced by many factors and these studies looked at dogs in a pet home environment therefore neuter status cannot be solely identified as the cause of aggression in these cases so the results must interpreted with caution. Two of the studies only looked at one specific breed, and the other study only consisted of 150 dogs therefore more research is required, but to produce a controlled study of behaviour may be difficult due to the number of factors involved. There is no indication that spaying will improve a dog's behaviour therefore spaying should not be suggested or used to try to improve behaviour problems (O'Farrell et al, 1990). A study looking at the trainability of dogs found that spaying of female dogs does not appear to have any detrimental effect on their trainability (Serpell and Hsu, 2005).