Rising global temperatures mean that many researchers are looking for ways to stop farmed chickens from overheating. This could involve exposing eggs to slightly higher temperatures during incubation, with previous research suggesting promising outcomes.
However, the behavioural consequences in adult chickens of this approach are less clear, particularly in terms of how it could affect the sociability and aggressiveness of males, which influences flock well-being.
To learn more about this, at KU Leuven, Belgium, and his colleagues put 60 high-quality chicken eggs in three identical incubators.
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They first set each incubator to the standard temperature of 37.6掳C used in hatcheries, which reflects the conditions experienced in a natural nest under a laying hen.
The researchers then increased the temperature of one incubator by 1掳C, while another was raised by 2掳C. Both were set to these temperatures for 8 hours a day, from days 15 to 20 after laying. Chicken eggs typically hatch on day 20 or 21. For the remaining 16 hours of the day, all the incubators were at 37.6掳C.
After hatching, all the chicks were kept in identical temperature-controlled conditions. Over the next six weeks, the researchers ran a series of behavioural tests.
The results show that the males exposed to the standard incubation temperature as eggs were generally less sociable than the equivalent females. Sociability was measured by how vocal the chicks were when isolated for 3 minutes and how much time they spent in a 鈥渟ocial zone鈥� close to other chicks during the tests.
The male chicks that were incubated at 1掳C or 2掳C above the standard temperature were almost twice as vocal as the female equvialents when isolated for 3 minutes.
The males in the 2掳C group also spent twice as much time in the social zone, compared with those in the 1掳C and standard hatchery temperature groups.
Given the crowded living conditions in most chicken farms, increased sociability may make these male birds less aggressive towards the females and therefore improve the overall welfare of the flock, says Norton.
Why a higher incubation temperature affects male behaviour is unclear, but temperature variations probably also occur in natural nests. 鈥淭he eggs in the middle lose heat more slowly than the eggs on the outside,鈥� says Norton. 鈥淥ur hypothesis is that maybe the end result is a group of chicks with different personalities.鈥�
The research focused on male chicks, although early results suggest similar effects may occur among females, but to a much lesser extent.
In commercial farms, adult males are often aggressive towards other chickens, including females, says Norton. If longer-term studies confirm the results of this research, slightly overheating incubated eggs could not only make chickens more resilient to climate change, but also improve their welfare, he says.
Coping with warmer conditions may also be beneficial as poultry production increasingly moves to hotter countries for global consumption, says Norton.
Applied Animal Behaviour Science
