Egg Incubation Physiology - Anatomy & Physiology

Changes in Composition of the Egg during Incubation

• As the embryo grows within the egg, the composition of the egg changes.
• Both yolk and albumin diminish.
  • Yolk providing energy for growth and maintenance of the embryo.
  • Albumin providing protein for the embryo and giving up water, which is lost through pores in the shell.
• Water is produced when yolk fat is oxidised.
• Water lost from the egg is replaced by air, creating the 'air cell' at the blunt end of the egg.
• Embryo punctures the chorioallantoic and internal shell membrane.
  • Able to begin pulmonary ventilation, rebreathing the 'air cell' gas.
  • Transition from diffusive respiration through the chorioallantois to breathing through the lungs.

Heat Transfer to the Egg

Heat Transfer to the Egg

• Transfer of heat from the body to the egg is the most important contribution of the incubating adult to incubation.
• Most birds develop a seasonal bare patch of skin known as the 'brood patch' on part of the thorax and abdomen.
  • 'Brood patch' is in direct contact with the egg to permit a greater heat transfer than if there were feathers between them.
• At the same time, there is an increase in the size and number of blood vessels in the bare skin.
  • Serves to increase heat transfer, as hot blood runs closer to the surface.
• Adult can adjust the rate of heat transfer by:
  • Standing or leaving the egg.
  • The closeness with which the 'brood patch' is applied to the egg.
  • Responding physiologically to the temperature of the egg, thus increasing or decreasing metabolic heat production.
• 'Brood patch' temperature is 34.9-42.4ºC.
  • This is 1.1-5.5ºC higher than the egg temperature.

Heat Loss from the Egg

• Heat loss from the egg is prevented by a thin boundary layer of air adjacent to the shell.
• If the egg is in a nest, the nest will also provide resistance to heat loss.