Improper nutrition of breeders e.g. the use of mouldy feed or feed lacking micronutrients
Eggs are cracked, dirty or wet.
Improper egg cleaning and fumigation.
Eggs stored improperly or for too long before incubation.
Improper incubation parameters such as too high or too low temperature or humidity or insufficient egg turning during the incubation period. (See questions number 21, 22 and 25 for more details on proper temperature, humidity and turning rate)