Here's why:
* Spaying removes the ovaries: The ovaries are the primary producers of hormones like estrogen and progesterone, which are crucial for lactation.
* Hormonal changes: Spaying eliminates these hormones, resulting in a significant reduction in milk production.
* Milk production requires hormonal stimulation: Even if a mammal had previously been pregnant and lactating, spaying eliminates the hormonal basis for milk production.
It's important to note that while spaying eliminates milk production, it doesn't always eliminate all maternal instincts. A spayed mammal might still exhibit behaviors like nesting or licking her young, but she will not be able to produce milk.