Multi stage and single stage incubation systems use similar equipment but are operated quite differently except that they both turn the embryos much the same. Multi-stage incubation systems must provide for the average needs of all embryos within the incubator, thus it may not meet the specific needs of the youngest and oldest embryos at the same time in the incubator.
Single stage incubation systems allow the hatchery manager to:
1. Alter specific incubator temperatures for a specific embryo age or for eggs that have been stored
2. Manipulate the ventilation damper to modify relative humidity, gas concentrations and provide a more uniform temperature throughout the incubator cabinet.
3. Generally the hatcher unit is constructed similar to the single stage setter and are typically more robust in providing a superior environment compared to the more classic type multi-stage hatchers.
The result of being able to provide specific set points the single stage incubation system can provide the embryo and chick:
1. improved nutrient utilization
2. improved organ system maturation at hatch
3. improved hatchling performance in the field.
When you manipulate or control the damper you will not only alter the amount of fresh air that moves through the incubator to change gas concentrations (CO2, O2, and H2O) but you also influence uniformity of heat distribution. Fresh air ventilation also makes it difficult to maintain relative humidity as one must maintain a specific damper opening that will support the oxygen needs of the oldest as well as the youngest embryos although it may not be optimal.
Single stage incubation systems allow you to restrict ventilation (oxygen) when there is reduced need for oxygen to help maintain a uniform environment within the incubator and to increase ventilation of the incubator as embryos tissue mass increases. At the same time, by restricting the damper opening during the early part of incubation to reduce air flow through the incubator it is easier to maintain elevated humidity without having to use humidifiers which will create localized areas of cooler air, creating unevenness in incubating temperature in different parts of the incubators.
Egg temperature: Single stage incubation allows one to alter incubator temperature to meet the needs of the developing embryo. We know that incubation temperature can impact thyroid development which can in turn affect how the hatchling responds to stressors in the broiler house (Iqbal et al., 1990, Christensen et al., 2005, Wineland et al., 2006a)
If you look at the heat production curve of developing eggs you will see that internal egg temperature will be below incubator set point early and above set point later in incubation (Romijn and Lokhorst, 1960). The temperature that the embryo is developing at can influence the embryo and hatchling (Wineland et al. 2006, Christensen et al. 2007, Oviedo et al. 2008).
Moisture loss from the egg: Moisture loss from the egg will be influenced by the eggshell porosity and the humidity that the incubators are set at. Eggshell porosity as measured by moisture loss or conductance of the eggshell informs us of the ability to allow gases to pass through the pores of the egg. Oxygen will move into the egg and carbon dioxide and water vapor will move out. The main effect upon moisture loss from eggs in any incubation system is the relative humidity the eggs are exposed to in the incubator cabinet. Elevated relative humidity reduces moisture loss and low relative humidity will increase moisture loss from a particular egg. While moisture loss at specific times of incubation is important it does not have to be lost uniformly over the incubation period. Single stage incubation allows one to manipulate the time of moisture loss from the egg which helps in maintaining temperature uniformity within the incubator when uniformity is needed most. Normally, ventilation dampers are closed during the initial 6-10 days of incubation and in some hatcheries the incubators do not operate humidification systems if the setter rooms are properly maintained. Closing the damper also allows the carbon dioxide concentration to increase which some people advocate during the early period of incubation. Typically using single stage incubation we see less moisture loss (8-10% average) from the eggs of a flock when compared to the same flock in a multi-stage incubation system (12-14% average). Eggs will lose moisture over a fairly wide range and the embryos have the ability to maintain specific body moisture content (Funderburk et al. 2007).
Low conductance eggs which demonstrate reduced moisture loss within a given environment can be reduced further by elevated relative humidity. It is critical to keep in mind that if an eggshell has reduced porosity (reduced eggshell conductance) it is restricting the amount of vital gases that pass in and out of the egg and to or from the developing embryo. This is critical during the period the embryo enters into the plateau of oxygen consumption. Eggshells which exhibit low conductance restricts the amount of oxygen to the developing embryo while a higher conductance eggshell allows more oxygen to the developing embryo. Oxygen is of course needed by the embryo so as to properly utilize nutrients for energy and tissue development (Christensen et al. 2005, Christensen et al. 2007, Wineland et al. 2006b). Incubators may have to be operated differently for different breeds as it has been demonstrated that different breeds exhibit different eggshell conductance. This can explain why some breeds are less susceptible to metabolic problems than other when incubators are not operated correctly.
Ventilation and gas concentration: Ventilation of an incubator has two components. The first is the ability of the fan to move air around within the incubator so that airflow is across all eggs as uniformly as possible. This allows us to provide heat to the very young embryo and remove excess metabolic heat from the older developing embryo. The removal of this excess metabolic heat is achieved through a combination of airflow and incubator set points. The second aspect of incubator ventilation is changing the vital gas concentrations to meet the needs of the developing embryo. The ability of the single stage incubation system to do this allows us to manage the development of the embryo much better. Increasing oxygen concentrations when needed will allow proper nutrient utilization.
Single stage and multistage incubation system comparison: Our group conducted a series of comparisons between Chickmaster multi-stage and single-stage systems in a commercial broiler hatchery. The results (Wineland et al. 2008) demonstrated improved body weight, feed conversion and leg health (see representative tables below from one of the experiments). Where you are able to control the incubation parameters more precisely for a specific age of embryo you can see improvements in performance. Single stage incubation will have an economic return if an investment is made, but like all incubation systems, the hatchery manager must be aware how his incubators are running and what his hatchling quality is like so he can fine tune the incubators.
Body weights during grow-out (SSMS 12)
Processing plant data (SSMS 12)
Where you are able to control the incubation parameters more precisely for a specific age of embryo you can see improvements in performance.
Christensen, V. L., M. J. Wineland, I. Yildrum, D. T. Ort and K. M. Mann, 2005. "Incubator temperature and oxygen concentrations at the plateau stage in oxygen uptake affect turkey embryo plasma T4 and T3 concentrations." Int. J. Poult. Sci. 4:268-273.
Christensen, V.L., M.J. Wineland, J.L. Grimes, E.O. Oviedo, P.S. Mozdziak, D.T. Ort and K.M. Mann 2007. Effect of Incubator Temperature and Oxygen Concentration at the Plateau Stage in Oxygen Consumption on Turkey Embryo Muscle Growth and Development. International Journal of Poultry Science 6 (6): 406-412, 2007
Funderburk, S.L., M. J. Wineland, J. Beavers, J. Shepard, H. R. Cutchin, K. M. Mann, V. L. Christensen, and E. O. Oviedo-Rondon, 2007. The impact of two incubator systems upon moisture content in eggs and chicks. Poult. Sci. (Suppl. 1.), 86:749
Iqbal, A., E. Decuypere, A.Abd El Azim, and E.R. Kuhn. 1990. Pre- and post-hatch high temperature exposure affects the thyroid hormones and corticosterone response to acute heat stress in growing chickens (Gallus domesticus). J. Therm. Biol. 15:149-153.
Oviedo-Rondón, E. O., J. Small, M.J. Wineland, V.L. Christensen, P.S. Mozdziak, M.D. Koci, S.V.L. Funderburk, D.T. Ort, and K.M. Mann. 2008. Broiler embryo bone development is influenced by incubator temperature, oxygen concentration and eggshell conductance at the plateau stage in oxygen consumption. British Poultry Science Journal 49(6):.666-676
Romijn, C., and W. Lokhorst. 1960. Foetal heat production in the fowl. J. Physiol. 150:239-249.
Wineland, M.J., V.L. Christensen, I. Yildirum, B.D. Fairchild, D.T. Ort and K. M. Mann. 2006a Incubator environment interacts with the genetic line of broiler at the plateau stage to affect embryo plasma thyroxine and triiodotyrosine concentrations. Int. J. of Poult. Sci. 5:714-722.
Wineland, M.J., V.L. Christensen, I. Yildirim, B.D. Fairchild, K.M. Mann and D.T. Ort, 2006b Incubator temperature and oxygen concentration at the plateau stage in oxygen consumption affects intestinal maturation of broiler chicks. Int. J. of Poult. Sci. 5:229-240
Wineland, M. J., E. O. Oviedo-Rondon, H. R. Cutchin, J. H. Small, K.M. Mann, and J. Beavers. 2008. A field comparison of hatch and broiler performance using both single stage and multi-stage incubation. Poultry Science 87, Sup. 1. Abstract 149, p. 48. Poultry Science Meeting July 2008
This presentation was given at the 9no SEMINARIO DE ACTUALIZACIÓN AVICOLA DE AMEVEA, Argentina. September 16th, 2010. Engormix.com thanks the authors and the organizing committee for the contribution.