The main issue was that, although hatchability was excellent, chick quality was not – primarily due to thick bellies. Lowering humidity set point in the setter from 53 per cent to 50 per cent delivered the quality this hatchery was looking for, with first week mortality in the farm reducing to significantly below their standard.

However as soon as “winter”, with daily temperatures of 18 to 25°C, was over, October brought a combination of high temperatures (30°C) and high humidity (up to 80 per cent). Phone calls described the same thick-belly problem again.

By logging-in to the hatchery’s control system remotely, Mr Barten could see that relative humidity remained well above the previously advised set point during the first days of incubation. Only when valve positions were opened in accordance with the incubation programme did relative humidity reduce to the required point. This was not so strange. Given that inlet air was both warm and humid, it needed little warming after entering the setter and therefore retained high humidity. Combined with water evaporation from the eggs, there was too much water in the air to achieve sufficient weight loss.

His advice was to open the air valves a further 10 to 20 per cent during the first days of incubation, to allow relative humidity to drop to its lowered set point. This once again resolved the issue of thick bellies, also demonstrating to the hatchery manager the importance of responding to external climate by running “winter” and “summer” ventilation programmes.

However external climatic conditions can change frequently – and unexpectedly. In daily hatchery practice, responding quickly enough to compensate for these changing conditions can be difficult.

In this case, a newly developed upgrade for the setter’s ventilation control provided a reliable solution. With this in place, humidity becomes the leading parameter for valve position, providing carbon dioxide remains below the designated maximum set-point. This is usually reached during the second half of incubation, as the embryo’s metabolism increases.

The next time Mr Barten received a call, the hatchery’s manager reported that life was much improved. With valve positions responding quickly and reliably to changes in external climatic conditions, chick quality was exactly where it should be, and now constantly, throughout the year.