Background

The effects of hatching at high altitude on hatchability and chick quality depend largely on the altitude at which the hatching eggs are produced - and how the hatchery manager adjusts the incubation programme.

Barometric pressure declines with altitude, as does the partial pressure of oxygen and absolute humidity. Fresh ventilating air will tend to be colder and drier than at sea level.

Oxygen availability

The oxygen content of air is always 21per cent, but reduced partial pressure at altitude provides less oxygen from a given volume of air. This pressure reduction results in lower levels of oxygen for the embryo, which is partially compensated by the embryo's higher capacity for binding oxygen to  blood haemoglobin (Dragon, et. Al (1999). Journal of Experimental Biology; 220: 2787 - 2795). At altitudes above 2000 meters, it can help to inject oxygen into the setter and the hatcher, to raise the oxygen level from 21 to 23 â€" 25 per cent. The main drawbacks of using oxygen are cost and safety. Its use may, therefore, be limited to hatching parent stock.

Water loss

It is reasonable to assume that the drier air at altitude will result in increased moisture loss from the eggs. However, it is important to realize that breeder flocks adapt to altitude by producing eggs with a lower effective pore area. This offsets increased diffusion and therefore water vapour loss through the egg shell at any altitude remains the same as at sea level (Reduction of Pore Area of the Avian Eggshell as an Adaptation to Altitude; H. Rahn et. al, 1977).

Conclusions

The following three scenarios are considered:

Eggs produced at sea level: hatchery at altitude (1000 to 2000 meters)
Of the three scenarios, this is the least desirable because it will definitely result in reduced hatchability. Eggs produced at sea level have a relatively large effective pore area and will therefore lose more water at higher altitudes. To compensate, setters and hatchers should be operated at a higher relative humidity. This is best achieved by pre-conditioning the inlet air to a relative humidity of 75 per cent, with a temperature of 24 - 28°C (optimum). At the same time, increase the ventilation rate from normal for sea level, to accomodate the reduced oxygen levels.

Eggs produced at same altitude as hatchery (1000 to 2000 meters)
In general this will give good results. Ventilation rates should be higher than normal for sea level. During humid external conditions, increase ventilation even more, as humidity reduces oxygen levels in the air still further. This higher ventilation rate may cause reduced humidity in the setters and hatchers. To avoid constant humidifying, humidity set points should be lowered and the resulting more than optimal weight loss (eg. 14 - 15%) is preferred in this case.

Eggs produced at altitude; hatchery at sea level
Generally, this will give good results. The set points for relative humidity need to be reduced to achieve optimum weight loss as the eggs have a reduced effective pore area.

Advice

Exact set points for relative humidity are dependent on a.o. altitude and egg shell conductivity (age flock, nutrition, genetics). It is therefore recommended that relative humidity set points are fine-tuned by weighing trays of eggs before setting and again at transfer at 18 , 18.5 days.
Optimum weight loss for good hatchability and chick quality is indicated in the table below.

Alternatively the size of the aircell provides an indicator of weight loss.â  If during an egg-breakout â too many wet, fully developed embryo's that fail to pip are observed, this indicates insufficient weight loss and/or a shortage of oxygen. In this case, set points for relative humidity should be reduced and/or ventilation rate should be increased.

For further information or advice, please contact the Pas Reform Academy.