A new study from the Royal Veterinary College has revealed that delaying spaying (neutering) of female dogs (bitches) until between seven and 18 months reduces the risk of early-onset urinary incontinence by 20%, compared with early-age spaying between three and six months.

Three-quarters of all bitches in the UK are spayed, with spaying offering both health-related benefits to the dog (eg avoiding uterine infections later in life) and behavioural benefits for owners (eg issues of the bitch coming in season twice yearly). However, some disadvantages have also been linked to spaying, with increased risk of urinary incontinence (leaking urine while lying down) reported following spaying.

Urinary incontinence affects one-in-thirty bitches in the UK, with spayed bitches over three times more likely to become urinary incontinent. 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 skin sores stemming from urine-soaked skin.

Once a decision to spay a bitch has been taken, the next question is about the best age to spay. Until now, there was some evidence linking age at spay and subsequent urinary incontinence in bitches but most previous veterinary studies only reported on the association between various factors rather than showing true causal links between spaying and urinary incontinence.

To fill this information gap, this new RVC study evaluated whether spaying between three and six months caused a difference in the risk of early-onset urinary incontinence (urinary incontinence diagnosed at any age up to eight years) compared with spaying between seven and 18 months.

Led by the RVC’s VetCompass Programme, the study explored anonymised veterinary clinical records from more than 30,000 bitches born from 2010 to 2012 under first-opinion veterinary care in the UK. As a world first for a study on urinary incontinence in bitches, the study applied a new research method that the RVC is developing called veterinary causal inference, which uses anonymised veterinary electronic clinical records to emulate a randomised controlled trial without requiring the participation of live animals.

Data were analysed from a random sample of 1,500 bitches to replicate a randomised clinical trial and explore the impact of delaying spaying from 3-6 months to instead be spayed from 7-18 months. The new causal inference method created two mirrored groups of study animals that were balanced for characteristics including breed, veterinary group and insurance status so that the researchers could compare the risk of urinary incontinence between bitches that differed only by the age of spaying.

The results showed that spaying between seven and 18 months caused a 20 percent reduction in the risk of early-onset urinary incontinence compared with spaying between three and six months. These new results will help vets to make evidence-based recommendations on the timing of spaying, and owners to make an informed decision, whilst taking other spaying considerations into account.

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 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.