Fearfulness in commercial laying hens: a meta-analysis comparing brown and white egg layers

Raising laying hens: housing complexity and genetic strain affect startle reflex amplitude and behavioural response to fear-inducing stimuli

“…We found no strain difference in the approach of the NO, which corresponds with some findings in the literature [27,59], though others reported browns to have shorter approach latencies [58], and a meta-analysis on strain differences in fear behaviour showed a lower approach rate in brown than white strains [28]. The same meta-analysis also suggested that strain differences in fear behaviour might be situation dependent [28]. Our results corroborate previous claims that different genetic strains might have different strategies to cope with specific stressors [28,60], as the results from the NA test did not match those from the NO test.…”

“…Additionally, while brown strains are phylogenetically removed from white strains, differences between distinct lines of brown hens or lines of white hens cannot be dismissed, which would add another layer of variation between studies. However, it appears that the perception of the stimulus could be different; what is frightening to a brown bird might not be as frightening to a white bird and vice versa [ 28 ]. We found no strain difference in the approach of the NO, which corresponds with some findings in the literature [ 27 , 59 ], though others reported browns to have shorter approach latencies [ 58 ], and a meta-analysis on strain differences in fear behaviour showed a lower approach rate in brown than white strains [ 28 ].…”

“…However, it appears that the perception of the stimulus could be different; what is frightening to a brown bird might not be as frightening to a white bird and vice versa [ 28 ]. We found no strain difference in the approach of the NO, which corresponds with some findings in the literature [ 27 , 59 ], though others reported browns to have shorter approach latencies [ 58 ], and a meta-analysis on strain differences in fear behaviour showed a lower approach rate in brown than white strains [ 28 ]. The same meta-analysis also suggested that strain differences in fear behaviour might be situation dependent [ 28 ].…”

“…in dogs (Canis familiaris) [23]), and different breeds vary in the level of developmental plasticity of fear behaviour (in sheep (Ovis aries) [24], in rats (Rattus norvegicus domestica) [25]). Similarly, in the commercial-laying hen, there have been many reports of differences in fear behaviour between different genetic strains and breeds of chicken [26][27][28]. Commercial-laying hens can be grouped into two phylogenetic groups that were domesticated in different regions of the world [29] and have either brown or white eggshells, usually corresponding to their feather colour [30].…”

“…Both phylogenetic groups contain multiple distinct strains, a term used in this paper to refer to specific genetic lines. While white hens have long been thought to be flightier and browns appear more docile [ 31 ], differences in fear behaviour between strains might depend on the type of fear-inducing stimulus [ 28 ]. In addition, different response patterns were reported: white hens fled (flew up to avoid) from a looming object, whereas brown birds froze [ 27 ].…”