Robyn Elmslie, DVM DACVIM (Oncology)
It is widely accepted among pet owners in the United States that dogs and cats should be neutered at an early age. The American Animal Hospital Association (AAHA), an organization that sets standards in Veterinary Medicine for family Veterinarians to uphold, writes on their website. “ The American Animal Hospital Association supports the concept of neutering cats and dogs as young as 8 weeks of age in order to help reduce the overpopulation problems in companion animals. Adopted by the American Animal Hospital Association Board of Directors, November 1994. Last revised March 2010.” This AAHA statement is supported by several studies (Stubbs WP et al., Semin Vet Surg Med, 1995; Howe LM et al 2001; Spain CV et al JAVMA 2004). Although AAHA does also write that the timing of neutering should be at the discretion of the family veterinarian, as with any recommendation, widespread application of the policy may have negative, unintended consequences.
The question of timing of castration is highlighted in a study published this month (Torres de la Riva G. et al. PLoS One Feb 2013) in which the authors examined the incidence of several diseases in castrated versus intact male Golden Retrievers. Their study included 145 intact males, 178 males castrated before 12 months of age and 70 dogs castrated after 12 months of age. The results were dramatic. Male Golden Retrievers castrated before 12 months of age were 3 times more likely to develop lymphoma, a common lymph node cancer, as compared to intact males or males castrated after 12 months of age. Similar results were found for specific orthopedic conditions (hip dysplasia and ACL rupture). Given the popularity of Golden Retrievers, these results are significant and will likely change the recommendations made by veterinarians to Golden Retriever puppy owners.
This is not the first time that the policy of early castration of male dogs has been questioned. Ru et al. (Ep Sante Anim 1997 and Vet J 1998) first reported an increase in the risk of the bone cancer osteosarcoma in neutered as compared to intact dogs. The impact of this study was reduced by the fact that many breeds of dogs were included in the analysis and several other risk factors for osteosarcoma such as patient height and weight were emphasized. Risk factors for the development of osteosarcoma in Rottweilers was studied and reported by Cooley DM et al (Can Epid Bio Prev 2002). The authors reported that neutered Rottweilers, both male and female, had a highly significant increased risk of developing osteosarcoma as compared to their intact counterparts. The authors cautioned that this finding was specific to the Rottweiler breed and could not be extrapolated to other breeds. Given the high incidence of bone cancer in Rottweilers, this study was the first important turning point in veterinary oncology in regards to recommended neutering practices for this breed for cancer prevention.
Finally, studies in dogs with transitional cell carcinoma (TCC) of the bladder or prostate have also revealed an increased incidence in neutered dogs as compared to intact male dogs (Norris AM et al. JVIM 1992 and Bryan JN et al. Prostate 2007).
The results of these studies highlight the importance of adapting breed-specific recommendations to pet owners, regarding the timing of castration of their new puppy, so their unique needs are addressed. While the castration recommendations for male Golden retrievers, male Rottweilers and breeds at risk for bladder and prostate TCC are evolving, the recommendations for female dogs is less clear. Female dogs have an increased risk of mammary cancer, ovarian cancers and pyometra when left intact. All issues must be taken into consideration when deciding on the timing of neutering female dogs. Future studies will clarify recommendations for the timing of neutering female dogs and males dogs of other breeds.