Acquired urinary incontinence (AUI) in the bitch is currently reported to affect 20% of all neutered bitches compared to <1% of intact bitches and males, however the full aetiology of AUI in the bitch remains undetermined.

Our previously reported in vitro work demonstrates that neutering a canine causes a decrease in bladder responsiveness to neurogenic field and muscarinic stimulation. The aim of this study was to determine if neutering alters the collagen percentile of the canine urinary bladder.

Sections of bladder were dissected from entire and neutered male and female dogs (ME, MN, FE and FN respectively), with informed owner consent. They were fixed, sectioned and stained with Masson Orange G. Images of the strips (5/bladder) were evaluated morphometrically and were captured and analyzed using image analyzing software to determine collagen percentage. Data are expressed as mean ± s.e. mean (n= number of dogs), and compared by ANOVA (Bonferroni post-test). * indicates significant difference (p<0.001) from entire.

Strikingly these results show that neutering a bitch causes increased collagen in the urinary bladder wall, whilst neutering a male dog does not. This suggests that changes in female reproductive hormones post neutering may play a role in the physical changes reported. It is hypothesized that the increase of collagen and concurrent proportional decrease in smooth muscle within the bladder of neutered bitches may play a role in the development of AUI.