Increasing Environmental Complexity by Providing Different Types of Litter and Perches during Early Rearing Boosts Coping Abilities in Domestic Fowl Chicks

Abstract

Early experience of a complex environment can improve biologically relevant traits related to coping abilities. However, the mechanisms underlying these positive effects have not been well explored. We hypothesized that giving chicks possibilities to express choices within relevant resources could be an important part of the mechanism, as well as a novel way to increase environmental complexity. In a balanced design, laying hen hatchlings of the white hybrid Bovans Robust were reared in a “single-choice” environment (single litter and perch type) or a “multi-choice” environment (four different litter and perch types). Immunological and behavioral indicators of chicks’ coping abilities were explored in this experimental study at three weeks of age. Chicks from “multi-choice” environments had shorter durations of tonic immobility, lower heterophil/lymphocyte ratios, higher natural antibody concentrations, and were more successful in gaining novel food rewards in a repeated opportunity test. These results imply that chicks having access to variation within resource types were less fearful, experienced less chronic stress, would be more able to cope with pathogenic challenges, and potentially had an improved learning ability. To conclude, the more complex environment, achieved by increasing chicks’ possibilities to choose, seemed to make chicks better prepared for potential challenges, boosting their adaptive capacities and their ability to make the most of opportunities.

Effects of the rearing environment complexity on laying hens’ spatial cognition: A holeboard test approach

“…This is supported by the fact that trial duration and the latency to the first baited cup also decreased over time, showing the birds were quicker to perform the task and to find the first bait. These results also support the idea that food deprivation prior to testing is not necessary for laying hens when the food reward is attractive (Arts et al, 2009;Nordquist et al, 2011;Tahamtani et al, 2015).…”

“…In our study, RM ratios stayed relatively low (0.4-0.7) during all phases, though we observed an increase across time. These results are comparable to the ones obtained in previous studies on chickens (Nordquist et al, 2011;Tahamtani et al, 2015), but remained lower to the ones obtained in some studies on pigs (over 0.8 in Gieling et al, 2013;Grimberg-Henrici et al, 2016). It could be that birds did not learn the position of the baits and encountered them by chance while exploring the arena.…”

“…This could be either due to higher fear levels or lower cognitive abilities of the cage-reared birds. Previous research has demonstrated that increased environmental complexity during rearing reduced fearfulness in laying hens (Brantsaeter et al, 2016;Nazar et al, 2022), which supports the idea that cage-reared hens might be more fearful. We saw that cage-reared birds started the Cued phase with a lower RM score than aviary reared birds but reached the same score by the end of the phase.…”

“…Previous studies on laying hens report WM ratios ranging between 0.7 and 0.8 (Nordquist et al, 2011;Tahamtani et al, 2015). The hens in our study demonstrated slightly higher WM ratios (0.8-0.9).…”

“…From 32-40 weeks, birds were tested in a holeboard test modified from Tahamtani et al (2015) and Nordquist et al (2011). It consisted of a habituation phase, followed by a training and testing phase.…”