3 ways to ‘spay’ a dog
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?