

rdft ^*^ 



Twin chicks, 19 days old, hatched from a double-yolked egg. Since double-yolkers are rarely 

 twice as large as ordinary eggs, the twins did not have enough room to develop, as evidenced 

 by the badly crippled female, left; the male, right, though otherwise normal, had crooked 

 outer toes. The mother of the chicks was a dominant White Plymouth Rock; the father, a New 

 Hampshire. Vhoto by John H. Vondell 



By F. P. JEFFREY, T. W. FOX, and J. R. SMYTH, JR. 

 Department of Poultry Husbandry 



TWIN CHICKS hatching from a 

 double-yolked egg broke the 

 dull routine of an experiment con- 

 ducted here last year in a study to 

 determine how long fertility lasts 

 during the early period of the lay- 

 ing year in hens. 



Of the 208 eggs set, only one pro- 

 duced the famous twins that are 

 supposed to be, undeniably, the first 

 chicken twins to survive hatching. 

 The remainder of the eggs did not 

 hatch. (Only one in every 500 eggs 

 laid by hens is a double-yolker.) 



Not since 1850, when Bernard in 

 Paris, France, reported the success- 

 ful hatching of double-yolked eggs 

 has there been any reference to such 

 an occurrence. 



Chicks of Different Sex 



Proof that the twins did not orig- 

 inate from a single yolk was evi- 

 denced in the different sexes and 

 different down colors. The male 

 was pure white; the female, clear 

 red; that is, red without any black 



in the primary and secondary wing 

 feathers. 



Double-Yolked Eggs Infertile 



Double-yolked eggs ^vere found 

 to be two-and-one-half times less 

 fertile than single-yolked eggs — a 

 good reason why commercial hatch- 

 eries avoid setting double-yolked 

 eggs. Moreover, embryos from such 

 eggs died during the first seven days 

 of incubation (a mortality rate that 

 was four times as heavy as that 

 found in ordinary eggs) . 



In spite of the high mortality, 

 however, 30 percent of the embryos 

 in double-yolked eggs survived at 

 least for 14 days or longer, and 

 many were fully developed before 

 dying. 



Double-yolked eggs are laid in 

 greatest numbers during the early 

 production period. In the flocks 

 studied, the incidence of double- 

 yolked eggs dining the first seven 

 weeks of egg prochiction was 2.8 

 percent, 



