Today's Veterinary Practice

MAY-JUN 2018

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PEER REVIEWED 42 THE NEUTERING CONTROVERSY HSA were identified, and spayed females were at a 1.6 to 2.2 times higher risk of developing HSA when compared to intact females. 13 The underlying pathophysiology of this apparent increased risk is unknown, and warrants further investigation. Studies with higher numbers of dogs affected with HSA are necessary to determine if a true link exists between gonadectomy and development of HSA. Osteosarcoma Osteosarcoma (OSA) is another type of neoplasia for which a possible increased risk after gonadectomy has been suggested. OSA primarily affects large-breed dogs, and it is associated with poor long-term survival rates despite aggressive treatment. Experimental studies have shown variable relationships between sex hormones and OSA, with some suggesting suppression and others promotion of the disease. 14 The pathophysiology of the potential link between sex hormone exposure and OSA risk in dogs has not been investigated. A large case-control study evaluating dogs from several institutions found the risk of developing OSA in gonadectomized dogs to be 2 times that of intact dogs, regardless of sex. 15 A study evaluating approximately 700 rottweilers with 86 confirmed cases of appendicular OSA found that gonadectomy before 12 months of age significantly increased the risk of developing OSA. 14 This study was conducted via owner questionnaire; however, veterinarians were contacted to confirm diagnoses. Interestingly, gonadectomized dogs in this study had a longer life expectancy than intact dogs. This may contribute to the apparent increased risk of OSA in gonadectomized dogs, as OSA is frequently diagnosed in geriatric patients. Mast Cell Tumors Mast cell tumors (MCT) represent approximately 25% of all cutaneous neoplasms in dogs, with prognosis varying based on grade. 16 A study including approximately 150 dogs with cutaneous MCT found that gonadectomized vizslas were 3.5 times more likely to be diagnosed with MCT than intact vizslas across both sexes in one study. 12 Additionally, gonadectomized vizslas were diagnosed with MCT at a significantly younger age than intact vizslas. Gonadectomy was not found to affect the rate of MCT diagnosis in Labrador retrievers. 17 A case-control study evaluating more than 300 dogs with MCT in multiple breeds found a 4 times higher risk of development of grade 2 or 3 MCT in spayed females over intact females and a 1.4 times higher risk in castrated males over intact males. 18 In contrast, gonadectomy did not significantly affect the diagnosis of MCT in a retrospective study evaluating golden retrievers. 11 A large study evaluating more than 400 dogs with MCT disease in England found fewer MCT diagnoses in neutered dogs than in intact dogs. 19 Collectively, these studies suggest neuter status may only be associated with diagnosis of MCT in certain breeds. Lymphosarcoma Lymphosarcoma (LSA) is the most common type of hematopoietic neoplasia in dogs. High-grade LSA may be fatal within weeks if not treated aggressively with chemotherapeutic agents, and even with appropriate treatment it is associated with a median survival time of approximately 1 year. 20 Male golden retrievers castrated before 12 months of age were 3 times more likely to be diagnosed with LSA compared to intact male golden retrievers; LSA was not diagnosed in males castrated after 12 months of age. 11 When evaluating LSA in vizslas, gonadectomized vizslas were 4.3 times more likely to be diagnosed with LSA than intact vizslas across both sexes. 12 Gonadectomy was not found to affect the rate of LSA diagnosis in Labrador retrievers. 17 Larger-scale studies evaluating the impact of gonadectomy on other canine breeds have not been performed. An increased risk of hip dysplasia and cranial cruciate ligament (CCL) rupture has been demonstrated in castrated male dogs. 34 The same study reported spayed females have an increased risk of CCL rupture, but no increased risk of hip dysplasia compared to intact females.

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