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 21 per 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 2,000 metres, it can help to inject oxygen into the setter and the hatcher, to raise the oxygen level from 21 to 23&ndah;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 realise 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 eggshell at any altitude remains the same as at sea level (see Reduction of Pore Area of the Avian Eggshell as an Adaptation to Altitude by H. Rahn et al., 1977).

Three ‘Altitude’ Scenarios

1. Eggs Produced at Sea Level; Hatchery at Altitude (1,000-2,000 metres)

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 accommodate the reduced oxygen levels.

2. Eggs Produced at Same Altitude as Hatchery (1,000-2,000 metres)

In general, this will give good results. Ventilation rates should be higher than normal for sea level. During humid external conditions, increase ventilation 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 higher–than–optimal weight loss, e.g. 14–15 per cent, is preferable in this case.

3. 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

• Fine–tune relative humidity set points by weighing trays of eggs before setting and again at transfer at 18.0 to 18.5 days. Exact set points for relative humidity are dependent on largely on altitude and eggshell conductivity (age flock, nutrition, genetics). Optimum weight loss for good hatchability and chick quality is indicated in the table below.
• Judge the size of the air cell as an indicator of weight loss.
• Be aware of signs that indicate insufficient weight loss and/or a shortage of oxygen during an egg break–out. These signs are: too many wet, fully developed embryo’s that fail to pip. If this is observed, reduce set points for relative humidity and/or increase ventilation rate.