Gonadectomy is common in the United States due to its value in surgical sterilization and preventing or reducing reproductive diseases (eg, benign prostatic hyperplasia, testicular tumors, pyometra, mammary neoplasia) and sexually driven behaviors.7 Adoption rates of shelter dogs are often increased with preadoption gonadectomy; however, evidence of its potential negative effects has been accumulating.7,30-40
Gonadectomy has been correlated with obesity in dogs and cats,30-32 which may result from changes in fasting metabolic rate (as has been noted in female cats), increased food intake, and/or decreased activity.31,32 Obesity may increase the risk for or exacerbate osteoarthritis and/or other systemic illnesses. Owners should be instructed on how to adjust activity levels and food intake to maintain their pet’s ideal body condition.
Another condition associated with neuter status is urinary incontinence in female dogs.33 Urinary incontinence is rare in intact bitches (0%-1%) but reportedly occurs in 5% to 20% of spayed female dogs.7,33,39,40 The risk appears to be greatest in dogs >33 lb (15 kg).40 Some studies have reported correlations with the dog’s age at the time of OHE, whereas others have found no significant effects.39-41 Signs of urinary incontinence can manifest as early as 4 weeks postoperation or may be delayed for 3 to 10 years.24,33 The pathophysiology of this acquired sphincter mechanism incompetence is unclear. Small-breed female dogs may have a greater risk for pyometra and mammary tumors than urinary incontinence; thus, the benefits of OHE before the first or second heat may outweigh the likelihood of complications.
Large- and giant-breed dogs, particularly golden retrievers, German shepherd dogs, and rottweilers, may be at greater risk for morbidity and mortality from joint disease, neoplasia, and urinary incontinence resulting from gonadectomy at a young age. Gonadectomy has been shown to increase the incidence of joint disorders in large-breed dogs by 2 to 5 times that of intact dogs, especially when performed in dogs <6 months of age.7,34,35 For example, in one study, the incidence of joint disorders was 5% in intact adult male golden retrievers as compared with 27% in those neutered before 6 months of age.34 In another study, joint disorders were diagnosed in 21% and 16% of male and female German shepherd dogs, respectively, gonadectomized at <1 year of age as compared with 7% and 5% of intact male and female German shepherd dogs, respectively.35
Gonadectomy may also be associated with an increased risk for certain cancers in large-breed dogs, although controlled studies are lacking. In one study of 683 rottweilers, bone sarcoma was diagnosed in 12.6% of dogs36; the risk for development of bone sarcomas was >3 times greater in dogs gonadectomized before 1 year of age. In other breeds, cancer-related deaths may be increased because gonadectomized animals live longer.7 Delaying gonadectomy until physical maturity (eg, >12 months of age) may be beneficial for large-breed dogs, although delaying surgery increases the risk for wound complications and surgical errors, likelihood of greater costs due to increased surgical time and anesthesia, and potential for unwanted litters before sterilization.
Because cats do not appear to experience many long-term ill effects from gonadectomy, other than the potential for obesity, prepubertal gonadectomy is usually considered acceptable for this species.37 However, gonadectomy in animals <7 months of age will delay physeal closure, which could increase the risk for physeal fractures in male cats, particularly if they become obese.42
Clinicians must weigh the risks and benefits of gonadectomy with the pet owner and determine the most appropriate age to neuter different breeds and species.