Dog Sterilization and Neutering: What About Mixed-Breed Dogs?

While the benefits of sterilization have been clear up until now, a growing body of evidence points against routine early sterilization. The only problem is that the results are not consistent or generalizable. Recommendations have been made based on breed. But what about mixed-breed dogs? An initial answer can be based on the dog’s weight. Sterilization of dogs—both male and female—is common practice. Often encouraged for reproductive reasons, this procedure also helps curb certain undesirable behaviors (aggression, running away, urine marking, hypersexuality) and can reduce certain health problems such as genital infections or tumors. A neutered dog is therefore more likely to live a long life and age more healthily. And until recently, the benefits of sterilization and neutering seemed clear-cut. However, recent studies are challenging some of these assumptions. Numerous studies now reveal that certain cancers and joint disorders are actually promoted by early sterilization in both male and female dogs. As the evidence mounts, sterilization before 6 months of age is becoming a cause for concern, raising questions about standard practice in the United States and much of Europe. However, the trends are not uniform across all dogs. The data do not appear to be consistent and vary by breed. A recent study by the School of Veterinary Medicine in California involving 35 different pedigree dogs confirms this. While each breed has its own characteristics, variations, and very specific risks, in general, smaller pedigree dogs seem less vulnerable to early sterilization (Read the detailed report on the 35 breeds here). But if your dog isn’t a “pedigree dog,” what should you do? Veterinarians also wanted to gather information on early sterilization and neutering of mixed-breed dogs. They therefore examined a sample of mixed-breed dogs, which they categorized by weight (<10 kg (739 dogs), 10–19 kg (546 dogs), 20 to 29 kg (992 dogs), 30 to 39 kg (604 dogs), and over 40 kg (258 dogs)), using the same diagnostic criteria for joint disorders and cancers as for pedigree dogs. Result: Sterilization does not appear to affect the development of one or more cancers in mixed-breed dogs, regardless of their weight or sex. However, in dogs weighing more than 20 kg, sterilization before 1 year of age was generally associated with a higher risk of developing one or more joint disorders. For larger dogs, this risk could be up to three times higher, depending on sex, with a higher risk for males. Smaller dogs were not at this risk. This information can be used to guide veterinary care and recommendations regarding the age at which dogs should be subject to sterilization, not only for veterinarians but also for shelters that take in many mixed-breed dogs and require that animals be subject to sterilization before adoption.