A new study from the Royal Veterinary College (RVC) has revealed that delaying spaying of bitches until between seven and 18 months causes a 20 percent reduction in the risk of early-onset urinary incontinence, compared with early-age spaying between three and six months (Pegram et al., 2024). The findings will help vets make evidence-based recommendations on the timing of spaying while taking into account other spaying considerations.
Urinary incontinence affects one in thirty bitches in the UK, with spayed bitches over three times more likely to experience this affliction. The condition can be distressing and costly for owners and can also harm the welfare of affected dogs due to an increased risk of urinary tract infections and urine scald. Previous RVC VetCompass research identified that Irish setters, Dalmatians, Hungarian vizslas, Dobermans, Weimaraners, Shar-peis and Boxers are the breeds at greatest risk of early-onset urinary incontinence, with increasing body weight also resulting in increased incontinence risk. However, the evidence on the timing of spaying relative to urinary incontinence risk has, to date, been less definitive.
Additionally, while clinical trials are typically considered the gold standard for determining causal treatment effects, they are not always practical or ethical. Therefore, this study is now one in a series that will use novel methods of causal inference, target trial emulation, to estimate real-world causal effects based on anonymised veterinary electronic clinical records. Causal inference from large databases can be viewed as an attempt to emulate a randomised controlled trial to answer a question of interest that often cannot be answered in any other way.
Conducting this study, researchers from the RVC’s VetCompass Programme, set out to research the impact of spaying on urinary incontinence in bitches, using the anonymised clinical records from more than 30,000 bitches under first-opinion veterinary care in the UK born from 2010 to 2012.
This included a random sample of 1,500 bitches spayed between three and 18 months. Of these, 612 (40.8 percent) bitches were spayed between three and six months and 888 (59.2 percent) at seven to 18 months. The analytic methods used in the study balanced the two groups of bitches across other characteristics, including breed, veterinary group, insurance status and chronic illnesses. This meant that the only remaining difference between the two groups was when they were spayed.
The results showed that bitches spayed between seven and 18 months had 0.80 times the likelihood of developing early-onset urinary incontinence compared with bitches spayed between three and six months. This means the bitches spayed later had a 20 percent reduction in the risk of early-onset urinary incontinence.
Camilla Pegram, VetCompass PhD student at the RVC and lead author of the paper, said:
“This study is now one in a series using an exciting new approach, allowing us to determine cause rather than being limited to association. Spaying is something that every owner and vet will need to consider at some stage and so the findings of this study can feed into spay decision-making. Although a decision to spay a bitch is based on many other factors other than urinary incontinence risk, the results suggest early-age spaying should be carefully considered and well justified.”
Dr Dan O’Neill, associate professor in Companion Animal Epidemiology at the RVC and co-author of the paper, said:
“These new findings help vets and owners to rely more on evidence rather than opinion when making decisions about when to spay bitches. The new scientific methods of causal inference developed by the RVC for this research series are also contributing to reducing the need to use live animals to answer vital research questions.”
Paula Boyden, veterinary director at Dogs Trust, said:
“Dogs Trust is delighted to have supported this evidence-based research, which will lead to improved dog welfare. The study will help vets and dog owners make informed decisions about the best time to neuter a dog to reduce the risk and prevalence of urinary incontinence developing throughout their lifetime.”
This research was supported by an award from Dogs Trust.
