A double yolker
is an egg
(usually a chicken
egg) which has two yolks
. Triple yolkers are rarer but not unheard of. Since the yolk is the site of the embryo
in a fertilized egg, this occurrence is roughly analogous to fraternal twins
or triplets in a human pregnancy.
Double yolkers are usually large or extra-large size eggs, produced by young chickens whose egg-laying cycles are not fully synchronized. They can also result from a diet over-rich in nutrients, since a chicken who thinks times are good might try to create more offspring than usual. Then again, some chickens just seem to produce double yolkers their whole lives.
some info from: http://www.goldenvalley.com/faq.html