Spaying Large-Breed Dogs Later in Their First Year May Decrease Incontinence Risk

According to a study published in the March/April issue of the Journal of Veterinary Internal Medicine, waiting to spay large-breed female dogs until later in their first year of life may decrease their risk of developing urethral sphincter mechanism incompetence (USMI). For smaller dogs, the age at spaying did not appear to affect incontinence risk.

“The most compelling clinical impact of the results of our study is the need to make age of neuter recommendations based on the projected adult weight of the bitch,” write the authors.

The investigators collected retrospective data about incontinent spayed female dogs from veterinary hospitals in the United States. Participating clinics also provided data from healthy spayed female dogs to serve as a control group. Dogs with urinary tract infections, hyperadrenocorticism, diabetes mellitus, or kidney disease, and those receiving corticosteroids or immunosuppressive drugs were excluded. In all, the researchers collected data from 163 incontinent dogs and 193 continent dogs.

The age at time of ovariohysterectomy was not significantly different between incontinent and continent dogs (median age: both groups, 8.5 months). However, incontinent dogs weighed significantly more than continent dogs at presentation (median weight: incontinent dogs, 25.4 kg; continent dogs, 17.7 kg). Body condition scores were the same in both groups (median score: both groups, 5). The age at presentation was not significantly different between the groups (median age: incontinent dogs, 72 months; continent dogs, 65 months). Among dogs with USMI, the median time from ovariohysterectomy to the first sign of incontinence was 3.73 years (range, 5-5417 days).

In a regression analysis, the researchers found a significant interaction between weight at time of presentation for incontinence and age at ovariohysterectomy. For dogs weighing over 25 kg, the hazard of developing USMI significantly decreased with every 1-month delay in ovariohysterectomy within the first year of life. For dogs weighing less than 25 kg, the hazard did not significantly change with the age at ovariohysterectomy.

Of the 163 incontinent dogs for whom treatment data were available, 75.5% received phenylpropanolamine, 21.5% received diethylstilbestrol, and 3.1% received both drugs. Although urinalysis was performed in nearly all incontinent dogs, systolic blood pressure was obtained in only 1 dog. The authors express concern that blood pressure is not monitored in more dogs receiving phenylpropanolamine.

Previous studies have indicated that large dogs are more likely than small dogs to develop USMI, say the authors. However, they write, this is the first study to examine how the interaction of body size and ovariohysterectomy timing affects USMI risk.

The authors conclude, “The data presented here show that the risk of USMI is not significantly decreased in smaller breed dogs by delaying [ovariohysterectomy], thus making the decision to neuter before initiation of estrus more appropriate. However, in dogs with projected adult weights >25 kg, the timing of neuter and its associated risks and benefits should be carefully considered and discussed with pet owners.”

Study limitations listed by the investigators include its retrospective nature, potential inaccuracies in data provided by the participating clinics, and the lack of a case-control population. The study was performed at the Ohio State University College of Veterinary Medicine and was partly funded by Merck Animal Health.

Dr. Laurie Anne Walden received her doctorate in veterinary medicine from North Carolina State University. After an internship in small animal medicine and surgery at Auburn University, she returned to North Carolina, where she has been in small animal primary care practice for over 20 years. Dr. Walden is also a board-certified editor in the life sciences and owner of Walden Medical Writing, LLC. She works as a full-time freelance medical writer and editor and continues to see patients a few days each