What Causes Oversized Hatching Eggs in Broiler Breeders?

Oversized eggs are due to a variety of possibilities in any breed of chicken. The causes vary from genetics, to stress, to accidents during the long egg formation within the hen, which takes 24 to 26 hours before the egg is laid. Only normal-sized, and well-shaped eggs should be used for hatching. Large eggs, whether double-yolked or composed of an egg inside another egg, Russian doll style, would never successfully incubate. Double-yolked eggs are chicken twins, which cannot develop and hatch. This is not a concern in general, as oversized eggs are considered idiopathic in nature and not a large issue in the broiler breeding shed. Large eggs are not generally symptomatic of disease.

  1. Ovulation Mishap

    • Double-yoked or eggs with more than one yolk are the result of the release of several yolks during ovulation. These multiple yolks journey down the oviduct where albumin is added and finally the shell. The two ovums can be fertile but will never develop due to the lack of proper space for twins to grow in the egg.

    Large Thin-Shell

    • Occasionally a large, thin-shelled egg will be laid by the hen, and is not a good choice to hatch. These eggs are possibly due to a long sequence of laying by the hen and she managed to produce an atypical egg. They are probably not nutritionally related unless the hen is repeatedly laying thin-shelled eggs. A veterinarian would be able to test this hen and others for calcium deficiency. Some older hens may have trouble using the proper nutrients to create good shell quality.

    Double Egg

    • A fully formed, shelled egg within another fully formed egg -- identical to the Russian nesting dolls -- rarely appears. These eggs are do to a mishap in the presentation of the egg or a merging in the ovulation, shell production process. These are discarded, and the hen should be observed for any complications.

    Genetics and Youth

    • Some young birds will lay small or unusual eggs. This is due to their newness to laying and their developmental stage. Hens almost exclusively outgrow these issues as they mature. There is a theory that hens that lay oversized or multiple-yolked eggs are genetically predisposed, as other animals, to the "twinning." If a hen consistently presents oversized eggs she may carry a gene for such eggs.