Objective For many generations, most species of farm animals have been subjected to intense and strictly targeted selection for improvement of their performance traits. This has led to substantial changes in animal anatomy and physiology, which resulted in considerable differences between the current animal breeds and their wild ancestors. The aim of the study was to determine whether there is breed-specific variability in behaviour as well as differences in emotional reactivity and preferences of laying hens. Methods The investigations involved 50 Green-legged Partridge, 50 Polbar, and 50 Leghorn hens. All birds were kept in the same conditions, and the behavioural tests were carried out at 30 weeks of age. We used the tonic immobility test and a modified open-field test including such objects as water, commercial feed, feed enriched with cereal grains, finely cut straw, and insect larvae, a sandpit, a mirror, and a shelter imitating a hen nest. Results The research results demonstrate that the birds of the analysed breeds differ not only in the excitability and emotional reactivity but, importantly, also in the preferences for environment-enriching elements. Ensuring hens’ well-being should therefore be based on environmental modifications that will facilitate acquisition of essential elements of chickens’ behaviour. The greatest emotional reactivity was found in the Leghorn breed, which may be a result of correlated selection aimed at an increase in chicken productivity. Conclusion The differences in the behaviour of the birds from the analysed breeds indicate that laying hens cannot be regarded as one group of animals with the same environmental requirements.

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

This study aimed to develop a methodology for using ultrasonic technology (USG) to record eggshell thickness for selection of layers. Genetic correlations between eggshell strength and its thickness have been reported to be around 0.8, making shell thickness a selection index candidate element. Applying ultrasonic devices to measure shell thickness leaves an egg intact for further handling. In this study, eggs from 2 purebred populations of Rhode Island White (RIW) and Rhode Island Red (RIR) hens were collected on a single day in the 33rd week of the farm laying calendar from 2,414 RIR and 4,525 RIW hens. Beginning from the large end of the egg, measurements were taken at 5 latitudes: 0º (USG0), 45º (USG45), 90º (USG90), 135º (USG135), and 180º (USG180). To estimate the repeatability of readings, measurements were repeated at each parallel on 3 meridians. Electronic micrometer measurement ( EMM: ) were taken with an electronic micrometer predominantly at the wider end of eggs from 2,397 RIR and 4,447 RIW hens. A multiple-trait statistical model fit the fixed effect of year-of-hatch × hatch-within-year, and random effects due to repeated measurements (except EMM) and an animal's additive genetic component. The shell was thinnest in the region where chicks break it upon hatching (USG0, USG45). Heritabilities of shell thickness in different regions of the shell ranged from 0.09 to 0.19 (EMM) in RIW and from 0.12 to 0.23 (EMM) in RIR and were highest for USG45 and USG0. Because the measurement repeatabilities were all above 0.90, our recommendation for balancing egg strength against hatching ease is to take a single measurement of USG45. Due to high positive genetic correlations between shell thickness in different regions of the shell its thickness in the pointed end region will be modified accordingly, in response to selection for USG45.

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