Level of stress in relation to emotional reactivity of hens

Abstract

The aim of the study was to associate behavioural reactions of laying hens with the level of stress and to answer the question whether it is possible to select reactions that will facilitate phenotypic assessment of the level of stress in these birds. The investigations were carried out in 50 Green-legged Partridge, 50 Polbar and 50 Leghorn birds. A modified open-field test (MOFT) and a tonic immobility test were applied. Next, the quality of feathers was evaluated and the level of corticosterone in the feathers was determined. The corticosterone level was assessed in relation to the genetic group and feather quality and in relation to the probability of the presence/absence of specific physiological-behavioural reactions. The analysis of the results revealed no correlations between the corticosterone level in the feathers and the quality of the feathers. In turn, there was a correlation between the hen breed and the corticosterone level in the feathers: a significant difference was found between Zk and Pb hens. It was demonstrated that the corticosterone level was significantly higher in birds that exhibited such behaviours as preening in the open-field test. To sum up the results, it can be concluded that such behaviours as feather preening and latency until tonic immobility occurs can be indicators of stress in laying hens. HIGHLIGHTSThere was a correlation between the breed and the corticosterone level in the feathers: there was a significant difference between the Green-legged Partridge (3.97 ± 0.17) and Polbar (4.50 ± 0.19) hens. No significant correlations were found between the corticosterone level and the behavioural reactivity in the analysed hens. It was demonstrated that the corticosterone level was significantly higher in birds that exhibited self-grooming behaviours in the open-field test (4.61) than in hens that did not show such behaviours (3.91). ARTICLE HISTORY

Behavioural Variability in Chicks vs. the Pattern of Behaviour in Adult Hens

“…Therefore, investigations mainly focus on adjustment of birds' temperament to the environment. However, as indicated by the present study and previous investigations conducted by the authors [3,5], there is another aspect, i.e., the environment is not universal for individual genotypes and determines hens' behaviour in various ways.…”

“…The Zk chicks turned out to be fast and active and definitely outcompeted the other breeds in both competitiveness tests (I and II). Importantly, Zk chicks come from parents with a lower corticosterone level in the feathers, in comparison with the Lg and Pb breeds [5]. Chicks' behaviour is modified already at the stage of embryonic development through transfer of hormones between the hen and the egg and the formation of the HPA axis involved in responses to stimuli [15][16][17].…”

“…Chicks of three breeds of laying hens were used in the experiments: 60 green-legged partridge (Zk), 60 Polbar (Pb), and 60 Leghorn (Lg) birds. The chicks hatched in a flock where hens were previously assessed with behavioural tests and the corticosterone levels in their feathers was determined, indicating significant differences in the temperament and stress level between the breeds [3,5].…”

“…It appears that birds' environmental needs may vary not only between species but also between breeds [3] and individuals of the same breed [4]. Previous investigations [3,5] have demonstrated that hens from three different breeds (green-legged partridge-Zk, Polbar-Pb, and Leghorn-Lg) kept in environments as identical as possible not only differed in the level of activity, emotional arousal, or degree of curiosity, but also preferred different enrichments of the environment, which collectively resulted in a different level of stress in the birds [5]. The Zk breed showed interest in objects that allowed scratching and searching, i.e., the birds preferred a container filled with finely shredded straw and woodchips as well as insect larvae but ignored a feed container, shelter box, or mirror.…”

“…Both breeds had a higher level of stress than the Zk chicks. The authors reported that the living environment fulfilled the needs of the Zk breed only, but failed to satisfy the needs of the Lg hens [3,5]. The birds were kept on bedding and thus the need of the Zk chickens to scratch and search was satisfied.…”