Spaying: Pros and cons

Summary of 'To spay or not to spay: the nurse's role in owner education.  Smith, N. J. (2015) The Veterinary Nurse V6.

Potential advantages of ovariohysterectomy in bitches:

• Possibly lower incidence of mammary tumours
• Lower risk of developing cancers of the mammary tissue (if spay is carried out early, preventative effects decline the later the bitch is spayed)
• Prevents pseudopregnancy
• Prevents pyometra
• Reduces the already low risk of cancers of the reproductive organs
• Promoted for population control - although owner education, strict legislation and breeding control are used successfully in many Northern European countries to reduce the stray dog population despite neutering being uncommon.  So there is an argument that neutering 'should not be viewed as the main method of population control; education and owner responsibility is the key'. 

Disadvantages of spaying - the evidence suggests (though care with interpretation as it is often not conclusive):

• Increases incidence of urinary incontinence from 1% in entire bitches to between 5-20% in spayed bitches.  Timing of spaying might be important.
• Cruciate ligament disease is more common in spayed that intact bitches. Time of spaying, breed and obesity are also risk factors.  Dogs that participate in agility commonly suffer from ligament injuries; it is possible that dogs that do these sorts of activities are also more likely to be neutered as they are around other dogs.
• Increased risk of hip dysplasia, especially when spaying is carried out young. Obesity is a factor that covaries.  High impact exercise has been identified as a risk factor for hip dysplasia as well.
• Increased risk of osteosarcoma (possibly)
• Increased risk of obesity.  Age and weight of owner and age of the dog are also contributory factors.  Recent studies suggest this is due to behaviorual changes - a decrease in activity and increase in food intake, rather than a decrease in metabolic rate. 
• Some studies show that spayed bitches are more likely to show aggressive behaviour and be reactive (but there are many factors that can influence behaviour so interpretation must be cautious).