Today's Veterinary Practice

MAY-JUN 2018

Today's Veterinary Practice provides comprehensive information to keep every small animal practitioner up to date on companion animal medicine and surgery as well as practice building and management.

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PEER REVIEWED 44 THE NEUTERING CONTROVERSY NONNEOPLASTIC DISORDERS Behavior The impact of gonadectomy on behavioral disorders is important to consider, as frustrations with behavior often lead to relinquishment of companion animals to shelters. Given the vast impact of training and experiences when evaluating behavior in dogs, the potential for significant bias in behavioral studies is high. Castration is associated with improvement in some undesirable behaviors, such as roaming, mounting, and urine marking in male dogs. 21 Inter-male aggression may also improve or resolve after castration, although other forms of aggression seem to be less affected. 22 Fear behavior during veterinary visits has not been associated with reproductive status. 23 A study in female German shepherd dogs demonstrated a possible increase in reactivity to unfamiliar people and dogs following ovariohysterectomy. 24 This study did not evaluate the dogs before surgery, was not blinded, and only evaluated 14 dogs. 24 Behavioral disorders, such as storm phobia, may be more common in vizslas gonadectomized before 6 months of age than in intact vizslas. 12 A case-control study evaluating a variety of dog breeds found a possible association between gonadectomy and separation anxiety, although the number of intact animals in both the case and control groups in this study was low. 25 Gonadectomy has also been discussed as a contributing factor to cognitive decline in geriatric dogs. One study suggested intact male dogs may have slower progression of cognitive impairment than castrated male dogs. 26 This study had relatively low numbers and was only able to comment on male dogs because of the lack of recruitment of intact females. Urogenital Disorders Urinary incontinence is a disorder with an incidence of up to 1% in intact female dogs, compared to >20% in spayed females. 27 There is conflicting evidence regarding the importance of early versus late spaying and its impact on development of urinary incontinence in female dogs, with some studies reporting an increased incidence and frequency of episodes of incontinence in early-spayed dogs, while other studies report no difference between early and late spaying. 27 Larger-breed dogs are at higher risk than smaller-breed dogs. 28,29 This condition can be quite frustrating for owners and veterinarians alike to manage; therefore, it should be taken into consideration when deciding to spay female dogs. Given the suspected association with gonadectomy, owners of dogs with signs of urinary incontinence as puppies may consider waiting at least until after the first heat cycle to perform spay surgery. Pyometra is a condition of female dogs that is prevented by gonadectomy. Pyometra carries an incidence of approximately 25% by 10 years of age in intact female dogs. Though pyometra can be cured by ovariohysterectomy, the morbidity rate of dogs treated for pyometra is quite high, with an overall mortality rate of 10% reported in one study. 30 BPH is a condition of male dogs that is prevented by castration. 31 BPH is diagnosed in nearly 100% of intact male dogs by the age of 9 years old. Although clinical signs are not always present, BPH predisposes dogs to prostatitis and may lead to dyschezia and subsequent perineal hernia due to tenesmus. Perineal hernias can lead to life-threatening entrapment of the urinary bladder, intestines, and other structures. 32 Immune-Mediated Diseases One study found an increased incidence of multiple immune-mediated disorders in gonadectomized dogs of both sexes, including atopic dermatitis, immune- mediated hemolytic anemia, hypothyroidism, immune-mediated thrombocytopenia, hypoadrenocorticism, and inflammatory bowel disease. 33 One possible explanation outlined in this study was a lack of sex hormone-induced involution of the thymus, as thymic hyperplasia has been associated with autoimmune disorders. While there is minimal to no strong evidence clearly linking gonadectomy to various diseases, owners of at-risk breeds should consider all factors.

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