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Mushy Chick Disease / Yolk Sack Infection

Mushy Chick Disease, also known as a yolk sack infection, can kill newborn chicks.

Mushy chick disease develops inside the egg as the chick develops. Chicks once born stagger about and look sleepy. They will be reluctant to move and stay under the heat source. Mortality follows, with the worst of it occurring within the first couple of days of the chicks life. Chicks that survive the first few days will usually never be as strong or healthy as the rest of the flock.


The infection is caused by contamination by several common bacteria types that enter through the porous eggshell inside the incubator or before the egg is placed into the incubator. Incubation conditions are ideal for breeding bacteria as well as incubating eggs. Once the egg is infected, some of the harmful bacteria can break down the yolk sac, which causes secondary infection to move in.


Only preventative treatment is possible. Ensure nest boxes are kept clean, eggs used for incubation are clean, and incubators are disinfected before use. Remember, the first week of a chick’s life is when it is most likely to pick up the infection as it has little or no immunity at this time. A post-mortem can be carried out by a specialist veterinary service to confirm yolk sac infection. Disinfect your incubator but ensure your hatching eggs are collected regularly and laid in a clean nest.

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