First of all, even it had been sterilized, they still have the want of sex. They will just need less often than they never have sterilized. Therefore, they will still mow. They mow because of they need some thing. Besides when they need food or drink, they may also mow when their toilet is too dirty. You know, they like clean. They may mow as they don't like the food you are giving them as want to have new food...