If the egg is fertile, it is the blastoderm, and if infertile, the blastodisc. In most psittacines, the reproductive tract of the hen includes only the left ovary and left oviduct. The parts of the oviduct include the infundibulum, magnum, isthmus, uterus and vagina. The embryo actually begins to develop before oviposition. The egg may be candled to assess fertility after it is laid, and in some cases, it may show development within a few days of being laid.
Fertility is ascertained by the development of blood vessels within the egg.
For best hatchability, it is best to leave eggs under the hen for at least 14 days, to ensure the health of the developing chick, but this is not always possible or economically advisable. By pulling eggs for artificial incubation, many birds can be induced to lay more eggs than would normally occur, this increasing productivity. Optimum temperatures that simulate those of the natural parents will produce the healthiest chicks. It should go without saying that the production of healthy, viable baby birds requires a healthy flock. Breeder birds should be examined, tested and treated for any disease uncovered.