How normal is dirty rear feathers for a white leghorn layer

[bobbieschicks]

My 20 week old pullet started laying Thanksgiving Day. Since that time she has had a dirty looking rear off and on. I've checked her vent area and it's not blocked or weird looking. But her rear feathers keep getting dirty/messy. Is it because she is the only layer pullet and the rooster is riding her too much? What do you think is causing this? Is this normal for white leghorns? What could be happening here? I changed her feed to Layer feed over the weekend and she's been getting more treats lately (yogurt with egg shells & oyster shells) - could this be causing the issues?

She's not laying regularly yet. Yesterday was the 1st time in 3 days that she laid and egg - it was "normal" but smaller and had lumps on the outside - calcium deposits? Today I found two softshelled eggs in the manure box.
https://www.backyardchickens.com/forum/viewtopic.php?id=605049 page #9 shows the eggs from today

Here's her back end.

 

[CMV]

Some birds have chronically poopy butts. I had a group of layers that refused to roost, so they had messy butts all the time from lying in their own waste at night. I had to do regular baths and feather trims on their butts to keep them from looking nasty.

Does she have diarrhea? Have you checked for worms?

I can tell you it is not likely related to your roo. It is something going on with her.

 

[bobbieschicks]

I did worm them all the day before Thanksgiving (Valbazen) and 10 days earlier (Wazine) & I did the Sevin dust both times and cleaned out the coop both times. I'll take a closer look at her in a few minutes and see if I can see anything going on with her feathers. I did check her vent yesterday and it was clear of obstructions and seemed fine. It was just the low down feathers that seemed dirty. Her poop is next to the egg in the picture and it seems excessive but in the normal range.

I'll see if giving her a dry bath with DE cleans her off sufficiently - I noticed her getting cleaner looking after dust bathing yesterday and then today that's what her butt looked like. I'm wondering if it's the change in feed from Purina Medicated Start & Grow to Layena w/Omega 3 that is throwing her digestive tract off.