More Than Eggs – Relationship Between Productivity and Learning in Laying Hens

Abstract

The intense selection of chickens for production traits, such as egg laying, is thought to cause undesirable side effects and changes in behavior. Trade-offs resulting from energy expenditure in productivity may influence other traits: in order to sustain energetic costs for high egg production, energy expenditure may be redirected away from specific behavioral traits. For example, such energetic trade-offs may change the hens’ cognitive abilities. Therefore, we hypothesized highly productive laying hens to show reduced learning performance in comparison to moderate productive lines. We examined the learning ability of four chicken lines that differed in laying performance (200 versus 300 eggs/year) and phylogenetic origin (brown/white layer; respectively, within performance). In total 61 hens were tested in semi-automated Skinner boxes in a three-phase learning paradigm (initial learning, reversal learning, extinction). To measure the hens’ learning performance within each phase, we compared the number of active decisions needed to fulfill a learning criteria (80% correct choices for learning, 70% no responses at extinction) using linear models. Differences between the proportions of hens per line that reached criterion on each phase of the learning tasks were analyzed by using a Kaplan–Meier (KM) survival analysis. A greater proportion of high productive hens achieved the learning criteria on each phase compared to less productive hens (Chi23 = 8.25, p = 0.041). Furthermore, high productive hens accomplished the learning criteria after fewer active decisions in the initial phase (p = 0.012) and in extinction (p = 0.004) compared to the less selected lines. Phylogenetic origin was associated with differences in learning in extinction. Our results contradict our hypothesis and indicate that the selection for productivity traits has led to changes in learning behavior and the high productive laying hens possessed a better learning strategy compared to moderate productive hens in a feeding-rewarding context. This better performance may be a response to constraints resulting from high selection as it may enable these hens to efficiently acquire additional energy resources. Underlying mechanisms for this may be directly related to differences in neuronal structure or indirectly to foraging strategies and changes in personality traits such as fearfulness and sociality.

Effects of Maternal Care During Rearing in White Leghorn and Brown Nick Layer Hens on Cognition, Sociality and Fear

“…The comfort of social contact for Leghorns is supported by Väisänen and Jensen [48], who also found young Leghorns prefer to be in close proximity with familiar conspecifics. More recently, social motivation was found to be greater in white egg layers compared to brown egg layers [12]. The BNs were consistently placid and seemingly unmotivated throughout the various tests, except when a familiar human was present.…”

“…Overall, however, interactions between brooded pullets were more antagonistic than among non-brooded pullets. Various chicken breeds and hybrids also show different behavioral fingerprints such as high or low fear [11], social and cognitive preferences and abilities, respectively [12,13,14]. There may also be an interaction between genetic background and the behavioral effects of maternal care, as Versace et al [15] report variation in the response to social stimuli of chicks from different breeds.…”

“…A follow-up study compared Lohmann Brown chicks with pure White Leghorns and also found the brown layers successfully learnt the magnetic cues to retrieve a reward whereas the white layers were unsuccessful [43]. Genetic differences in learning have also been demonstrated in layer hens using Skinner boxes, with high-productivity lines showing faster acquisition of an operant learning task than low-productivity lines [12].…”

Smaller brains in laying hens: New insights into the influence of pure breeding and housing conditions on brain size and brain composition

“…Trade-offs resulting from energy expenditure for productivity may influence other traits: To sustain energy costs for high egg production, energy expenditure may be redirected away from specific behavioral traits. For example, such energy trade-offs may change the hens' cognitive abilities ( Dudde et al., 2018 ), which could manifest in smaller brain volumes. Here, we have shown that these lines have small brains and have suggested that, perhaps, this is one reason for the difficulty of adapting these hens to new housing systems in an appropriate manner, and it is possible that this brain size reduction has functional consequences.…”

“…In recent years, several studies have shown an influence of housing system on spatial learning ability behavior and levels of working memory in laying hens ( Krause et al., 2006 , Tahamtani et al., 2015 , Campbell et al., 2018 , Dudde et al., 2018 ). In addition, different housing environments can also be accompanied by variations in the brains of laying hens, such as in the hippocampus and the nidopallium caudolaterale ( Patzke et al., 2009 ).…”