Usually small, about110 of an ordinary egg, and some of them are too long or too round at the beginning. There are also normal, usually lacking egg yolk.

Chickens lay this kind of egg because foreign bodies, such as exfoliated mucosal tissue, small blood clots (caused by follicular bleeding during ovulation), and worms in the intestine (sometimes occasionally migrating upward to reach the fallopian tube) fall into the fallopian tube, which stimulates the protein secretion part of the fallopian tube and uterus, secretes protein and eggshells, and wraps them around the foreign bodies, thus forming a yolk-free egg, which is not a disease but only an accidental coincidence.

Yellow-free eggs are usually small eggs, but small eggs are not necessarily yellow. Sometimes, it is found that some yolk is wrapped in protein in small eggs. This kind of small egg with yolk is caused by the hen's frightened flight when the yolk matures and falls off, so that part of the mature yolk falls in the abdominal cavity and the other part falls in the fallopian tube. Such a small amount of egg fragments are also close to normal eggs, which can stimulate the fallopian tube to secrete protein, thus forming a small egg with a small amount of yolk. If this rare abnormal egg is often laid, it may be due to the narrow or blocked egg transfusion.