Later-age spaying of bitches reduces risk of early-onset urinary incontinence, according to new research

9 August 2024

There is growing evidence supporting an association between the age at neutering bitches and subsequent urinary incontinence (UI). However, the evidence for the optimal age and timing to neuter bitches remains inconsistent and previous observational studies have been limited to reporting associations rather than causal effects.

A new study by researchers at the Royal Veterinary College has compared the causal effects between neutering at early age (3 to <7 months) and at later age (≥7 to ≤18 months) on subsequent diagnosis with early-onset UI in bitches¹. The study attempted to overcome the limitations of previous research by using causal inference methodology with a target trial emulation approach. This approach aims to simulate a hypothetical randomised controlled trial by using observational data and can be used to answer a question that often cannot be answered in any other way.

A cohort of 30,953 bitches in primary veterinary care in the VetCompass database, born from 2010 to 2012 and neutered between 3 and 18 months old, were included in the study. Electronic health records were searched using search terms relevant to the diagnosis and management of UI in the clinical notes and treatment fields. The emulated trial included 1,500 bitches overall, comprising 612 neutered early (at 3 to <7 months) and 888 neutered later (at ≥ 7 to ≤ 18 months).

The median age at neutering in the “early” group was 6.1 months and in the “later” group was 12.0 months. The causal odds ratio in bitches neutered later versus early was 0.80, meaning that the odds of developing early-onset UI are 20% lower in bitches neutered later. Therefore, later-age neutering (≥7 to ≤ 8 months) causes reduced odds of early-onset UI diagnosis compared with early-age neutering (3 to <7 months).

This study is one of the first to demonstrate successful application of the target trial approach to veterinary observational data, although it is limited by possible issues with the retrospective analysis of electronic health record data, such as unobserved confounding, missing or misclassified data.

Take home message

Whilst neutering decisions should be carefully considered and are influenced by various factors as well as UI risk, these findings suggest that preference should be given to delaying neutering until after 7 months of age, unless other major reasons justify earlier. These findings can help vets make evidence-based recommendations on the timing of spaying.

Read the full study: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0305526#sec014

Reference

Pegram C, Diaz-Ordaz K, Brodbelt DC, Change Y-M, Hall JL, Church DB and O’Neill DG. (2024) Later-age neutering causes lower risk of early‐onset urinary incontinence than early neutering–a VetCompass target trial emulation study. PLOS ONE. https://doi.org/10.1371/journal.pone.0305526