Egg Incubation Physiology - Anatomy & Physiology
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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.