In layer hen commercial production systems, chicks are exposed to different stressors. One example, is that they are not raised by any living adult animals and do not receive maternal care. In the wild, chicks experience a sensetive period for the first 3 days of life, where they undergo filial imprinting. The chicks create a social bond with the hen during this time period, and they receive high levels of maternal care for the first weeks of their lives. The social bond and the maternal care influence the emotional development of the chicks.
During the sensitive period, environmental stimuli have stronger effects on developing chicks than at any other time during the chicks’ lives. This experience, only taking place at this specific ontogenetic phase, has a particular impact on chicks’ cognitive, social, and neural development.
Filial imprinting is when chicks learn to progressively approach and follow a particular conspicuous stimulus with certain general properties. It is most often the first stimulus they have visual, auditory, or tactile experience with, which typically is the hen or other chicks, but it can also be other stimuli, like artificial objects. Filial imprnting behaviors remain until adulthood. The social bond between a chick and its stimulus can be critical for the chick’s survival. Filial imprinting have been observed occurring in domesticated chicks.
Chicks learn from their mothers, for example, how to socially interact and peck, which have a great impact on the behavior of the chicks. Chicks receive safety and warmth from their mothers. These factors affect sociability, cognition, and emotional stability in chicks.
Globally, billions of chicks are hatched annually in industrial settings with highly standardized methods. The eggs are incubated in darkness in incubators that can fit tens of thousands of eggs, and the temperature and humidity are heavily controlled. There is a rather loud noise level inside the incubators (~90 dB). It is common to fumigate the incubators with formalin as disinfection during the 3 days before the hatching date. The hatched chicks are tilted from racks onto a conveyer belt system. Here, they are sorted by sex, vaccinated, beak trimmed (not in Sweden, but it is common in most countries), and placed in boxes for transport. The commercial hatchery procedure is stressful for the chicks, which influences their levels of corticosterone (CORT), behavior, cognitive judgment bias, and weight. The effects can be long-lasting. The stress can, for example, lead to severe feather pecking, which is a welfare problem that can cause injuries and even lead to death in chickens.
If chicks in layer hen commercial hatcheries were to imprint on a model hen, it could potentially affect the emotional state of the chicks positively, because of the importance of the filial imprinting process. Imprinting could then possibly be used to counteract the early life stress chicks experience in layer hen commercial hatcheries, and thus improve chick welfare.
Chicks imprinting on a stimulus, have been shown to affect their weight. Higuchi (1976) performed an experiment where some of the chicks were imprinted on a live dove. The imprinted chicks weighed more compared to the non-imprinted chicks.
The aim of this project was to examine short- and long-term effects of filial imprinting on a model hen on the emotional state of White Leghorn chicks (Gallus gallus domesticus), hatched at Linköping University, Sweden.
- (1) The imprinted chicks would be more optimistic than the non-imprinted chicks.
- (2) The imprinted chicks would show less fearful behavior compared to the non-imprinted chicks.
- (3) The imprinted chicks would weigh more than the non-imprinted chicks.