Mushy Chick infected chick
Yolk Sac Infection, Omphallitis
Yolk Sac Infection is a bacterial infection of the nabel and yolk sac of a chick. Turkeys, ducks, and chicks can develop the infection usually one to three days after hatching and the infection can be any number of bacteria commonly found in a chicken coop. Mortality is high and as many as 10% of the chicks might come down with the disease. Poor hygiene in the breeder flock or hatchery is the main cause but the bacteria could be picked up from dirty brooders or poor incubation practices.
The signs are listlessness, closed eyes, no appetite, diarrhea, pasty poop on the chickens vent area, and a swollen stomach. Once infected the chicks are probably going to die in less than one week and antibiotics are of limited use as it is a systemic infection, not localized.
The best preventative measures re sanitation and hygiene from breeding flock right through hatching and hardening the chicks off. Eggs that are extremely soiled with manure are more likely to pass the bacteria on to the yolk inside the egg. Culling is the most humane thing to do with a mush chick. If you don’t have the heart to snap it’s neck use a ziplock bag and put the chick in the freezer to end its misery.