Ventilation: interaction of gas exchange and temperature control
Beware of overheating
The heat production of an embryo increases as it grows. The embryo absorbs oxygen and, in addition to heat, releases carbon dioxide (CO2) and water (H2O) to the air. Fresh air must be supplied and used air must be extracted otherwise the embryo will suffocate. At the same time, fresh air introduced for ventilation should have the least possible direct impact on the embryo temperature and should not cause temperature fluctuations and variations in the incubator. At the start of the incubation process, the incubator is kept closed as much as possible (air inlet closed) to exclude cold air. A high relative humidity caused by the eggs losing moisture ensures the eggs heat up to incubation temperature uniformly. This requires an incubator with a high heating capacity, as an incubator loaded with 60,000 eggs of 60 grams has to heat up an egg mass of 3,600 kg. Eggs have the thermal properties of water, and just try heating up 3.6 cubic metres of water by a few degrees… If the eggs are heated too quickly (within 4-6 hours) to incubation temperature, there is a high risk they will start to sweat. In an incubator with a high heating capacity and high heat transfer, it is best to heat the eggs gradually, or increase the heat in small stages, up to incubation temperature in 20-24 hours. It will take at least the same amount of time in an incubator with a low heating capacity and low heat transfer, but in these conditions the embryos will start development with less uniformity. The optimal heating profile varies from one incubator to another (and per parent stock age), so always follow the manufacturer’s advice.
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Between day 16 and day 18, when the embryos produce a lot of heat, measure the EST to see if any dangerous hot spots are developing. Monitor the temperature of the eggs in the centre of the trays at various locations in the incubator. If the average eggshell exceeds 39.2°C (102.5°F), the hatchability and chick quality will suffer. This has consequences not only for the incubation result, but also for chick development and the mortality rate later at the broiler farm. The growth and feed conversion performance of these chicks will also be poorer.
If the ventilation rate is set high to remove heat and moisture there is a risk of larger differences in EST being created in the incubator. This may cause some eggs to be incubated too cold. Regulate this by not opening the air inlets too much (air circulation inside the incubator for more uniform heat distribution). Or pre-treat the incoming air.
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Not every infrared thermometer is the same. An IR thermometer that can measure this remotely (right) is useful, but not very accurate. An ear thermometer is better. Also make sure that it is acclimatised (e.g. put it in the incubator for a while), because if condensation forms on the thermometer itself, the measurement is incorrect. Advanced thermometers preheat automatically to prevent this. A digital screen does not automatically mean that the measurement is accurate!
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Ha tc he ry S i gnal s
