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Optimum Humidity for Ostrich Incubation

by 5m Editor
9 May 2008, at 12:00am

By Pas Reform. Ostriches are indigenous to Africa, although today it is not uncommon to find them being farmed commercially around the world for meat and leather production.

Background

In the wild, ostriches hatch their own eggs through natural incubation, in which both male and female take ‘shifts’. However under commercial conditions, almost all ostrich farmers rely on artificial incubation.

During artificial incubation, it is important to ensure that the eggs lose enough weight by evaporating water through the pores in the egg shell. Sufficient weight loss is necessary to obtain an air space which is big enough to facilitate internal pipping, after which the chick gradually changes over from respiration through the chorion-allantois to lung respiration as it prepares for the final step, external pipping.

Unfortunately there is little available research on optimal weight loss in ostriches. But in practice, good results are obtained with a weight loss of 15 per cent from setting to external pipping. However, depending on climatic conditions, incubator operators often find it hard to achieve such high weight loss and losing too little weight results in lower hatchability and oedematous chicks. When opening unhatched eggs, it is common to find full grown chicks that failed to pip the air cell. These chicks actually drown in their own eggs.

Advice

Weight loss during incubation depends on the relative humidity of the air around the eggs and the porosity of the egg shell. Natural variation in the porosity of different eggs means it is impossible to give exact recommendations for optimum relative humidity. But in general, relative humidity in ostrich incubation should be between 25 and 35 per cent.

To find the correct level of relative humidity, weigh a few eggs individually before setting and again at regular intervals. Calculate the average percentage of weight loss - which should be 0.37 %. for each day of incubation - to achieve the desired weight loss of 15 % at external pipping (around 41 days of incubation). If the actual average weight loss is too low, adjustments can still be made to correct this. Make sure that enough eggs are weighed to represent a viable average, as there may be considerable variation in the weight loss of individual eggs!

The temperature and relative humidity of the air in the room in which the incubator is situated also affects the humidity inside the incubator. From the Mollier diagram (summarized in table), it can be concluded that with a room temperature of 25ºC and 50%RH, the humidity in the setter at incubation temperature will drop to 24.4%. Some evaporated water from the eggs will raise this to a higher level. Likewise, humidity in the setter will be higher at higher room humidity levels, but also at higher room temperatures with equal room humidity.

With this in mind, the following is recommended:

  • Ventilate the room to ensure that outlet air (containing water evaporated from the eggs) does not become inlet air.

  • Aim for a room climate 25ºC/ 50% RH or any other combination that results in a maximum relative humidity of 25% at incubation temperature by using the Mollier diagram. On warm and/or humid days, an air conditioner may be required, to cool and dehumidify at the same time. Remember, the incubator’s humidifying system can only increase humidity. It cannot decrease it!

  • Ventilate the setter sufficiently to remove water produced by eggs. More ventilation causes: a) lower humidity in setter , and b) higher weight loss of eggs.

If weight loss at transfer is less then 10%, H.R. Wilson, University of Florida, suggests as an emergency measure in his “Incubation and hatching of Ratites”, to drill about four holes of 2mm diameter in the shell over the aircell at the time of transfer to the hatcher. At that moment, it is already too late to correct insufficient weight loss, but this does allow the chick to survive by lung respiration after pipping into the (small) air cell. Many of these embryos will require some assistance in hatching, because they will be malpositioned to some degree, due to their oedematous condition.

Temperature room % RH Room RH (%) in setter*
0 50 18
20 60 21.7
20 70 25.4
20 80 29.0
25 50 24.4
25 60 29.3
25 70 34.2
25 80 39.1
30 50 32.7
30 60 39.3
30 70 45.8
30 80 52.3

*after warming to incubation temperature

April 2008