Is this normal

My heifer is bred, well I think she is, but she has almost always had a "fat" area around her tail..

 

She is 3yrs old...

 

It looks like the older she gets the bigger it gets. is this a normal thing..

 

I have looked at other cows around here and they don't seen to have the same fat tail area, but then again mine is a bit plumper than the ones I've looked at..

 

 

Is this normal