You should change them after every feeding because they should be washed after every feeding.
Every day.
your nipples often swell up when you are cold, and often tickling them helps
How often should you change the fuel filter?
Monthly
if you want to be safe, every day or so
as often as needed
You should change your oil every 3,000 miles. If you drive your car rough, then you should change it more often.
everyday
How often should you change water pump in a boat
Every week
The average motorist should change the oil every 3000 miles. Oil should be changed more often if driven in dusty condition.
A female dog's nipples get bigger when she is pregnant because the puppies can more easily get ahold of bigger nipples to nurse from their mother, plus milk collects in the body of the mother and that makes the area bigger.