BALANCING DISEASE RISKS AND WELFARE: A COMPREHENSIVE REVIEW OF EARLY AGE SPAY AND NEUTER SURGERY IN DOGS
Biswadeep Jena, Ph.D.
Assistant Professor, Department of Veterinary Surgery and Radiology,
C.V.Sc. and A.H., OUAT, Bhubaneswar, Odisha
Abstract
Early-age spaying and neutering (EASN) of dogs has long been promoted as a responsible practice to manage pet overpopulation. However, emerging evidence calls for a more nuanced evaluation of its long-term health implications. This comprehensive review critically examines the scientific literature on the potential adverse outcomes of EASN in dogs, encompassing oncologic, orthopedic, behavioral, and systemic considerations.
A growing body of data suggests a significant increase in the risk of several cancers, including hemangiosarcoma, osteosarcoma, transitional cell carcinoma, and lymphoma in dogs neutered before sexual maturity. Additionally, orthopedic disorders such as hip dysplasia, cranial cruciate ligament rupture, and patellar luxation are more prevalent among dogs spayed or neutered at a young age, possibly due to delayed physeal closure and abnormal growth patterns. Behavioral studies further reveal heightened occurrences of anxiety, fearfulness, and aggression in early-neutered dogs, contrary to the common belief that neutering improves behavior. Systemic health concerns, including hypothyroidism, urinary incontinence, vaccine reactions, and increased susceptibility to obesity and pancreatitis, have also been associated with gonadectomy.
Importantly, while early neutering may marginally reduce the risk of mammary tumors, the supporting evidence is weak and often confounded by methodological biases. In contrast, the risks of other malignancies with poorer prognoses are significantly elevated. These findings underscore the need for individualized veterinary decision-making that considers breed, sex, intended use, and living conditions.
Given the multifactorial implications, this review advocates against a one-size-fits-all approach to spaying and neutering. Instead, it calls for a balanced, evidence-based dialogue between veterinarians and pet owners to optimize animal health and welfare while addressing population control. In regions like India, where stray dog management is critical, timing and context-specific recommendations become especially relevant.
Key words: Behavioral effects, Canine, Cancer risk, gonadectomy, neutering, Orthopaedic disorders, Veterinary population control
Early-age neutering is an established strategy aimed at managing pet overpopulation and its associated challenges (Olson et al., 2001). While there is a growing body of literature discussing potential risks associated with early spaying and neutering in dogs, it is essential to consider the broader context, particularly in regions with large stray dog populations like India. This article reevaluates the available scientific data, focusing on the implications for neuter surgery, while recognizing the complexities of animal welfare and population control.
In light of our responsibility for canine well-being, a continuous and critical appraisal of emerging scientific research is imperative to ensure the best care for our furry companions. This article thoroughly examines the accumulating scientific data, collectively suggesting the need for veterinarians and dog owners to reevaluate the prevailing notion that non-breeding dogs should undergo early neutering.
Cancer considerations
Prymak et al. (1988) noted that spayed females exhibited a 2.2x elevated risk of splenic hemangiosarcoma. Ru et al. (1998) indicated that spayed/neutered dogs faced a 2.2x higher likelihood of bone cancer compared to intact dogs.
Ware and Hopper (1999) highlighted that spayed females were over 5x more susceptible to developing cardiac hemangiosarcoma than intact females. Neutered males exhibited a 1.6x heightened risk of cardiac hemangiosarcoma compared to intact males.
Knapp et al. (2000) pointed out that spayed/neutered dogs carried a more than 4x amplified risk of developing transitional cell carcinoma of the bladder compared to intact dogs.
Cooley et al. (2002) conducted research on Rottweilers and discovered that both male and female dogs neutered or spayed before 1 year of age had a fourfold higher risk of developing bone sarcoma compared to sexually intact dogs.
Teske et al. (2002) undertook a 5-year study involving 15,363 male dogs, revealing that neutered males experienced prostate cancer about four times more frequently than intact males, countering the popular belief that neutering prevents prostate cancer. Sorenmo et al. (2003) supported these findings.
Bryan et al. (2007) observed that neutered dogs exhibited a 2.8x heightened risk of prostate cancer compared to intact dogs. Neutered dogs also carried a 3.6x increased risk of transitional cell carcinoma of the bladder and a 3x greater risk of any bladder tumor compared to intact dogs.
De La Riva et al. (2013) found that male Golden Retrievers neutered before reaching 1 year of age faced a 3x higher susceptibility to lymphosarcoma. They also revealed that spayed/neutered dogs were 3.5% more prone to mast cell cancer and 4.3x more likely to suffer from lymphoma.
According to Zink et al. (2014), a retrospective study of 2,505 dogs highlighted that early neutering significantly heightened the likelihood of developing cancers like mast cell cancer, lymphoma, and hemangiosarcoma. Furthermore, dogs neutered before 6 months of age were predisposed to behavioral disorders, challenging the proponents of early spaying or neutering.
Hart et al. (2014) demonstrated that female Labrador Retrievers spayed between two and eight years of age exhibited a notably increased prevalence of mast cell cancer, hemangiosarcoma, and lymphoma.
A particular study noted a slight increase in the risk of mammary cancer in female dogs after one heat cycle (8% increase), a greater risk with two heat cycles (26% increase), and an elevated risk with each subsequent heat cycle (Schneider et al., 1969). However, a recent systematic review of publications endorsing neutering as a means to reduce the risk of mammary tumours in dogs revealed that nine out of thirteen reports displayed a high risk of bias, while the remaining four had a moderate risk of bias (Beauvais et al., 2012). This review concluded that the evidence supporting the notion that neutering decreases the risk of mammary cancer is weak and doesn’t provide a solid foundation for definitive recommendations.
In any case, the increased risk figures for mammary cancer should be juxtaposed with the 200% to 400% heightened risk of other cancers in spayed females. While around 30% of mammary cancers are malignant (Misdorp, 2002), akin to human cases, early detection and surgical removal result in favourable prognoses (Peña et al., 2012). This stands in contrast to other listed cancers such as hemangiosarcoma, lymphosarcoma, and bladder cancer, which typically have fatal outcomes.
Orthopaedic considerations
Van Hagen et al. (2005) conducted a study involving 1733 dogs, revealing that canines sterilized prior to six months of age exhibited a 70% heightened susceptibility to developing hip dysplasia. De La Riva et al. (2013), incorporating 759 dogs, reported that dogs spayed or neutered before reaching 12 months of age had double the risk of hip dysplasia compared to their intact counterparts. These studies by Van Hagen et al. (2005) and De La Riva et al. (2013) suggest that early-age gonadectomy might lead to a delayed closure of growth plates, subsequently contributing to an elevated risk of orthopaedic issues such as hip dysplasia.
Numerous studies have also established a correlation between neutering and cranial cruciate ligament (CCL) tears. Whitehair et al. (1993) examined 10,769 dogs with CCL tears and found that spayed and neutered dogs of all ages were twice as likely to experience cranial cruciate ligament rupture. Duval et al. (1999) reported an increased risk of CCL rupture in neutered males and females, in comparison to sexually intact males and females, respectively. Slauterbeck et al. (2004) observed a higher incidence of cruciate tears in females that had undergone ovariohysterectomy and males that had undergone orchiectomy when compared to sexually intact dogs. Duerr et al. (2007) assessed tibial plateau angle in 116 dogs, concluding that early neutering significantly raised the risk of excessive TPA development in large-breed dogs with cranial cruciate ligament disease. De La Riva et al. (2013) found that within a population of dogs spayed or neutered before 12 months of age, 5% of males and 8% of females experienced CCL tears. Notably, no instances of CCL tears were reported within the intact dog population under study.
Vidoni et al. (2006) and O’Neill et al. (2016) demonstrated that spayed/neutered dogs were more than three times as likely to encounter patellar luxation. In Labrador and golden retrievers, neutering before six months of age increased the incidence of one or more joint disorders by 2x and 4x to 5x, respectively (Hart et al., 2014). In a study encompassing 1,170 German shepherds monitored up to eight years of age, 21% of neutered males and 16% of spayed females were diagnosed with one or more joint disorders, in contrast to 7% of intact males and 5% of intact females (Hart et al., 2016).
Dogs that have been spayed or neutered at or before reaching puberty frequently exhibit distinct characteristics such as elongated limbs, lighter bone structure, narrower chests, and narrower skulls in comparison to intact dogs of the same breed. This variance in growth often leads to significant modifications in body proportions, particularly in the lengths (and consequently weights) of specific bones relative to others. A review of existing literature indicates that the femur bone typically reaches its genetically determined normal length around 8 months of age, coinciding with the timeframe during which dogs are often spayed or neutered. On the other hand, the tibia normally ceases its growth between the ages of 12 to 14 months. However, early spaying/neutering leads to continued growth in dimensions and weight of the tibia. This abnormal growth pattern results in an irregular stifle angle, inducing greater stress on the cranial cruciate ligament and patellar tendon, thereby elevating the dog’s susceptibility to cranial cruciate ligament tears and/or patellar luxation (Martin et al., 1987; Salmeri et al., 1991; Zink, 2017). The same rationale applies to the findings of Glickman et al. (1999), who reported in a study involving 1,444 golden retrievers that bitches and dogs spayed or neutered before one year of age were significantly taller compared to those spayed or neutered after the age of one.
It is widely acknowledged that spayed and neutered dogs are more prone to being overweight or obese compared to sexually intact dogs (Lund et al., 2006). This excess weight can act as an additional contributing factor to the development of orthopaedic disorders. Thus, maintaining a lean body condition in spayed/neutered dogs can help alleviate the heightened risk of orthopaedic conditions.
Behavioural considerations
Teske et al. (2002) additionally documented that neutered dog displayed more traits of aggressiveness, fearfulness, excitability, and lower trainability compared to intact dogs. Neutering had been previously associated with cognitive impairment (Hart, 2001) and even a three-fold risk of hypothyroidism, often linked to behavioural alterations (Beaver & Haug, 2003).
Early-age gonadectomy has been linked to an elevated occurrence of noise phobias and undesirable sexual behaviours, such as mounting (Spain et al., 2004). Notably, spayed and neutered bitches and dogs exhibited significantly more behavioural issues, with fearful behaviour being most prevalent among spayed bitches and aggression in neutered dogs (Hsu & Serpell, 2003; Duffy & Serpell, 2006).
In a prospective study, German shepherds spayed between five and ten months of age demonstrated significantly heightened reactivity (Kim et al., 2006). In line with the aforementioned study, Zink et al. (2014) also found that neutered dogs were more prone to developing behaviour disorders compared to intact dogs. These disorders encompassed fear of storms, separation anxiety, fear of noises, timidity, excitability, aggression, hyperactivity, and fear biting.
Contrary to popular belief, the aforementioned reports challenge the notion that neutering reduces aggression and other behavioural problems.
Other health considerations
Female and, at times, male dogs that undergo spaying/neutering before puberty exhibit an elevated likelihood of urinary incontinence, with the condition being more pronounced in bitches spayed at an earlier age (Thrusfield, 1985; Thrusfield et al., 1998; Stöcklin-Gautschi et al., 2001).
Spayed female dogs demonstrated a notably heightened risk of hypothyroidism in comparison to intact females (Milne & Hayes, 1981). An extensive health survey involving several thousand golden retrievers indicated an increased propensity for hypothyroidism in spayed or neutered dogs (Glickman et al., 1999). Neutered males and spayed females exhibited greater relative risks of developing hypothyroidism compared to intact females (Panciera, 1994).
Neutered females displayed a 22-fold increased susceptibility to fatal acute pancreatitis when compared to intact females (Hess et al., 1999).
The risk of adverse reactions to vaccines is 27% to 38% higher in neutered dogs compared to intact dogs (Moore et al., 2005).
In a study involving female Rottweilers, a robust positive correlation was established between the retention of ovaries and increased longevity (Waters et al., 2009).
Conclusion
In light of the nuanced considerations discussed, it is clear that a balanced approach to neuter surgery is warranted. While the literature highlights potential risks, it is important to recognize that spaying and neutering remain valuable tools in responsible pet ownership and population control. Veterinary practitioners should engage in informed discussions with pet owners, considering factors such as breed, age, and health status to determine the optimal timing and approach for neuter surgery
Veterinarians must engage in comprehensive discussions with clients regarding the advantages and potential drawbacks of gonadectomy. Such conversations should take into account the specific breed of the dog, the owner’s unique circumstances, and the intended purpose of the dog. Hence, informing pet parents about the considerations surrounding early spaying and neutering is imperative, empowering them to make an educated decision regarding whether to proceed with or abstain from spaying or neutering their cherished pets.
It holds significant importance that we evaluate each dog individually, considering their distinct living environment. This involves a careful assessment of the risks and benefits associated with gonad removal. It is crucial to recognize that a one-size-fits-all approach is not applicable in every case, as the circumstances and requirements of each dog are varied.
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