Influences of environmental hatching system factors on multitasking ability and side biases in laying hen chicks hatched on-farm

Abstract

As an alternative to conventional hatcheries, eggs can be placed in a rearing barn on day 18 of incubation (ED18; embryonic development) to hatch on-farm, which eliminates the need of transportation of day-old chicks. In addition, on-farm hatched chicks are exposed to continuous light during late incubation, and have immediate access to feed, water, and litter, which might affect developmental processes. On-farm hatching is currently not commercially implemented in the laying hen sector. However, advancements in in ovo sexing technologies are expected to enable its future adoption. Building on this context, this exploratory study aimed to examine influences of these environmental hatching system factors on the behavioral development, with focus on multitasking abilities and lateralized behavior in layer chicks until eight weeks of age. Hatching eggs (n = 600) were assigned to one of the following treatments from ED18 - ED21 (3 pens/treatment): fully enriched with all factors (ALL), continuous light (L), immediate feed and water access post-hatch (FW), immediate litter access post-hatch (LIT), or fully deprived of all factors (CON). Seventy-five focal chicks (n = 5/pen) were subjected to three behavioral tests: multitasking test at nine days of age, retention test at ten days of age, and step detour test at five and seven weeks of age. Most focal chicks did not meet the multitasking test and retention test criteria, as they did not complete the assigned tasks. Potentially, isolation stress could have overwhelmed the ability of focal chicks to perform during these tests despite habituation. During the step detour test, foot preferences to cross the step and direction preferences to detour the barrier were both affected by week of age (p = 0.06 and p = 0.04, respectively) but not by treatment, with focal chicks showing more preferences at seven than five weeks of age. The lateralized responses during the step detour test involve both motor and visual cognitive aspects. Therefore, visual assessment and motivation to approach the social stimulus might have affected the responses. Additionally, corticosterone secretion in response to chick processing and in-ovo transportation at ED18 might have affected visual lateralization. Our study underlines the dynamic nature and multidimensionality of lateralized behavior in chicks. Currently, it is unclear how the transportation of eggs at ED18 interacted with the hatching system factors during our study and more research is needed to investigate underlying mechanisms.