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By Dr. Ron Meijerhof , Poultry Performance Plus, Voorst, the Netherlands
To maintain their body temperature at a certain level, chicks have to find a balance between their heat production and the heat loss. A real accurate standard for heat production of a day-old chick is not available, but an estimated heat production of 0.3 watt for a day old chick that has not yet eaten seems to be a workable average. To warm up a body, a certain amount of energy is needed. For chickens this so called specific heat is 3.35 kJ per kg of chicken per degree Celsius. So to warm up 1 kg of day old chicks with 1ºC we need to add 3.35 kJ of energy. If we assume that a day old chick weighs on average 40 grams, it means warming up a chicken by 1ºC takes 0.134 kJ or 134 Joule.A day old chick produces 0.3 watt of heat, which is equal to 0.3 Joule of heat per second. If this heat is not completely removed the body will go up in temperature. If no heat is lost at all and the bird produces 0.3 Joule per second, with a specific heat of 134 Joule per chicken, it will take roughly 450 seconds (134 Joule / 0.3 Joule per second) or 7.5 minutes to increase their body temperature by 1ºC.Increasing heat production
We do see that if the body temperature of the chick rises, it’s metabolism increases as well, resulting in more heat production. Exact figures on this are not known, but by looking at the incubation process (which is more intensively studied) we can assume that this heat production will increase with 10 to maximum 20% if body temperatures goes up. This means that the increase in body temperature by 1ºC will take even less than 7.5 minutes if no heat is removed. Of course, a situation where no heat is removed at all is just theory. But if the temperature of the air is equal to the temperature of the body, no heat will be lost directly to the air, and the chick has to find other ways to lose that surplus of heat.
We do see that if the body temperature of the chick rises, it’s metabolism increases as well, resulting in more heat production. Exact figures on this are not known, but by looking at the incubation process (which is more intensively studied) we can assume that this heat production will increase with 10 to maximum 20% if body temperatures goes up. This means that the increase in body temperature by 1ºC will take even less than 7.5 minutes if no heat is removed. Of course, a situation where no heat is removed at all is just theory. But if the temperature of the air is equal to the temperature of the body, no heat will be lost directly to the air, and the chick has to find other ways to lose that surplus of heat.
Breathing through nostrils
Luckily enough, nature has created an alternative way of heat loss. If water is evaporated, this has a cooling effect as it costs energy. When a chick is at optimum temperature, it breaths through its nostrils and by doing so, it evaporates about 1 to 2 gram of water in 24 hours. This means that it slowly loses water and would dehydrate but digestion of the residual yolk produces about 1 gram of metabolic water per 24 hour, so the bird is kept nicely in balance.
Luckily enough, nature has created an alternative way of heat loss. If water is evaporated, this has a cooling effect as it costs energy. When a chick is at optimum temperature, it breaths through its nostrils and by doing so, it evaporates about 1 to 2 gram of water in 24 hours. This means that it slowly loses water and would dehydrate but digestion of the residual yolk produces about 1 gram of metabolic water per 24 hour, so the bird is kept nicely in balance.
Evaporation of water costs energy, 2260 Joule per gram. This means that if a chicken evaporates 1 gram in 24 hour, it will lose 0.026 Joule per second (2260 J /24 h/3600 s). As its heat production is 0.3 Joule per second, this is not enough to lose all the generated heat, but when a chick breaths normally, its water loss by breathing contributes to about 10% of the total heat loss needed.However, if heat loss from the skin is not sufficient to lose the remaining 90% of the heat production, for instance because air temperature is too high, the body temperature will start to increase. The first reaction of the birds will be to spread out the wings and feathers a bit more, to increase surface area for heat loss, but if body temperature moves up to approximately 106ºF (41.1ºC), it will start panting as well. Panting is the birds substitute for sweating, and it cools the body by increasing the amount of moisture evaporated.
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Source: World Poultry, Vol. 27, No. 3, 2011
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