training-your-property:

All good playthings know that ‘no’ is not a permitted word.  But that doesn’t mean they can’t convey their disagreement. 

She may find it degrading at first, but men pay more attention to her udders than her words.  You’re just helping her to understand that they hold more value to her existence. 

In the end, it should enjoy and even giggle at using them to say no in such a way.  Just as much as she says yes by hopping up and down.  She may not agree with a point, but it shows she embraces the place you’ve put her.