Spay or Wait One Heat Cycle

Last Modified: September 17, 2006


Dear OncoLink "Ask The Experts,"

I have an 11-month-old female white German Shepherd dog who I do not plan to breed. I was told by the breeder to allow her to go through one initial heat cycle before neutering her, so that she could fully develop her bone structure, muscle, and size.

I am now hearing that my dog may pay the price by being prone to mammary tumors in the future. Who is correct?


Lili Duda, VMD, Section Editor of the OncoLink Veterinary Oncology Menu, responds:

Spaying is removal of the ovaries and uterus, or more recently in this country - and standard practice in European countries ? removal of just the ovaries. It is a very well-established fact that "spaying" a dog before the first, second, or third heats provides a significant decrease in the risk of developing mammary carcinoma later in life.

The risk reduction is greatest when performed before the first heat, and decreases gradually until there is no risk reduction if performed after the fourth heat. However, it should be noted that for dogs with breast cancer who have not been previously spayed, there may be a survival benefit to spaying at the time of surgery.

Many breeders recommend allowing a female dog to go through one heat cycle to allow for full maturation of body structure. While this makes intuitive sense, there is little empirical data published on this topic. Furthermore, there has been a recent trend to neuter (spaying females and castrating males) animals as young as 8 to 12 weeks of age in the animal shelter setting, in an attempt to alleviate pet overpopulation. There is a modest amount of data to suggest that this procedure is safe and relatively free of significant side effects later in life, but this is still a matter of significant controversy.