I have a 4 week old Orust chick with a swolen butt and abdomen. Eats good, poops good and doesn't act sick.
Iwould keep a close eye on it. Chicks younger than this can suffer from omphalitis or mushy chick disease, but most die whithing the first 2 weeks of life. Chicks all have air sacs throughout the body, and those can leak under the skin, usually from an injury, causing puffiness. Does it feel like air or fluid, or does it feel normal? Here is some reading for you: https://www.backyardchickens.com/a/mushy-chick-disease-yolk-sack-infection-omphalitis http://ijasvm.com/ijasvmadmin/upload/IJASVM_5113cbc51d31b.pdf https://www.backyardchickens.com/t/171121/deflating-subcutaneous-emphysema http://www.thepoultrysite.com/publications/6/diseases-of-poultry/223/subcutaneous-emphysema
