In North America, veterinarians are generally trained to remove the uterus and ovaries (spay) whereas in Europe, the removal of the ovaries (and sparing the uterus) is often the norm.
Some advocate to spare the ovaries for health reasons (and remove only the uterus) which means females will go through heat cycles, attract males and chaos, but be infertile.
Since chaos around females in heat is often a public safety issue and dog welfare problem, not removing the ovaries seems inappropriate for a successful dog population management program.
But why not just remove the ovaries and leave the uterus behind (ovariectomy, not ovariohysterectomy) which means a less invasive surgery for the free-roaming females?
The answer may be found in a study done on a statistically significant number of dogs in Chile.
It concluded the majority of dogs displayed no long-term (up to 6 months) testosterone levels change after chemical sterilization.
Does castration help reduce roaming?
The implications? We need to better understand the role testosterone plays on sexual, aggressive and
roaming behaviours to appropriately chose the best method of sterilization and intended impact on male dogs beyond shooting blanks.
Our team does not believe, at this point, that chemical sterilization is an ideal choice for free-roaming rez dogs: if a chemically castrated dog continues to pursue females in heat and engage in dog aggression, it remains a public safety issue.
Dr. Judith Samson-French
Effects of surgical and chemical sterilization on the behavior of free-roaming male dogs in Puerto Natales, Chile.
Garde E1, Pérez GE2, Vanderstichel R3, Dalla Villa PF4, Serpell JA5.