Hen with large mass on lower abdomen

[cat_named_noodles]

Well, hasn't been a good week for my birds
While treating with Tylan 50 last night for respiratory illness, I noticed my barred rock hen has a softball size mass under her skin on her lower abdomen between her breastbone and vent. It is kind of soft. I haven't gotten any puctures yet. She is acting pretty normal but I don't think she has laid an egg in several weeks. I thought this was because the flock is going through a molt. But I am not sure if she has molted yet. Her fluffy butt hid the mass until I was able to palpate it last night. I am wondering what are the most common things that can cause such a mass/growth. It is pretty round, like a softball, and not very hard. It doesn't seem to bother her that much. Ascites? Tumor? Internal laying? Anyway to tell besides necropsy or xray? My closest avian vet is an hour and a half from here. She may have diarrhea as some poo is on her feathers below her vent, but this could be because of the location of the mass or related to the illness the flockbis having. I am keeping her inside for observation right now.

 

[Eggcessive]

I suppose it is not her crop hanging down? There are some hens than develop a growth under the vent which can be a cyst, hernia, or a teratoma. Also if it feels like air, there can be a leaking air sac from an injury, but those are more to the side. Ascites is fluid that is leaked into the abdomen, and usually makes the whole abdomen full and tight like a drum. Here below are some pictures showing these various problems.
Also some threads to look at:
https://www.backyardchickens.com/t/120841/bald-butt-and-swollen-below-vent
https://www.backyardchickens.com/t/685262/severe-bulge-under-chickens-vent-pictures-please-help
https://www.backyardchickens.com/t/120841/bald-butt-and-swollen-below-vent/20
https://www.backyardchickens.com/t/171121/deflating-subcutaneous-emphysema
http://ijasvm.com/ijasvmadmin/upload/IJASVM_5113cbc51d31b.pdf

Ascites--photo by Casportpony

unknown large mass

 

[cat_named_noodles]

Wow thanks for all the links and info. I will check her and see if she is egg bound when I get home. I wonder if she hurt herself laying huge eggs. A couple weeks ago we were getting double-yolkers almost every other day but couldn't tell who was laying them. If so coild be a hernia from straining. I will have too check her out more closely tonight when I get home and take some pictures. Those pictures are pretty similar but she still has feathers on it.