More eggs but less social and more fearful? Differences in behavioral traits in relation to the phylogenetic background and productivity level in laying hens

Variation in litter occupancy and dust bathing patterns among layer strains following periods of litter restriction

Producers are moving toward cage-free systems to house laying hens. These include aviary styles with multilevel wire enclosures and litter areas on the floor. In aviaries with doors hens can be confined within the tiered enclosure, which can be done to promote oviposition in nests and prevent hens from laying eggs in litter. However, there are multiple genetic strains of laying hen used in the egg industry, and some show different temporal patterns for key behaviors that could affect when they want to be on litter. For example, though dust bathing by laying hens is typically considered to peak in early afternoon, there may be variation in timing of motivation to dust bathe among strains. Differences in hens' temporal patterns, coupled with aviary configurations or management practices, may restricts birds' ability to perform important behaviors, such as dust bathing (DB), when they would most prefer to do them. Our objective was to determine if there were strain differences in the temporal pattern of DB. We examined the timing of DB in 4 strains of laying hen (Hy-Line Brown [HB], Bovans Brown [BB], DeKalb White [DW], and Hy-Line W36 [W36]) housed in aviaries using 144 hens of each strain per aviary unit (4 units/strain). We recorded the number of hens DB and on litter using instantaneous scan sampling every 5 min using video collected at 26 and 28 wk of age beginning at 11:35 (when litter access began each day) to 20:00 (lights off). Brown strains acclimated to litter access more slowly than white strains. Hens of all strains DB most often soon after gaining access to litter, and more white hens (DW and W36) DB simultaneously and in the presence of more conspecifics. Further examination of diurnal rhythm of behaviors, such as dust bathing, under unconstrained conditions by a range of genetic strains of laying hens is needed to design management practices and aviary styles that best meet hens' needs.

Exploratory Study on Individual Locomotor Activity in Local Dual-Purpose and Commercial Breeder Pullets

Improving animal welfare is a prerequisite for the societal acceptance of poultry production. Support for improvements requires practical tools to quantify animal welfare and identify predispositions at the individual level, where possible. In this study, the activities and behavior of dual-purpose chickens (N = 245) and commercial breeders (N = 224) were analyzed. The general locomotor activity (GLA) data were collected using an RFID system over five days with 9-to-14-week-old animals. The results show that the animals of comparable age and stocking density differed from each other in their activity (p ≤ 0.001) according to breed, but no sex differences were observed (p = 0.159). No correlations were found between GLA and plumage condition (p > 0.05). The individual variations within the breeds are presented and discussed on an animal-by-animal level, providing new insights into the individual behavioral variability of chickens. The RFID systems can reliably generate GLA data that help to understand the potential interplay between behavior and animal welfare. The technology is also suitable for creating individual (personality) profiles that can be used for breeding. With a better understanding of the role of activity, husbandry and management practices can be adapted to improve animal welfare.

Understanding Circadian and Circannual Behavioral Cycles of Captive Giant Pandas (Ailuropoda melanoleuca) Can Help to Promote Good Welfare

Circadian and circannual cycles of behavior regulate many aspects of welfare including metabolism, breeding, and behavioral interactions. In this study, we aim to demonstrate how systematically determining circadian and circannual cycles can provide insight into animals' needs and be part of an evidence-based approach to welfare assessment. We measured and analyzed the observational behavioral data of 13 zoo-housed giant pandas (Ailuropoda melanoleuca), across life stages and between sexes, each month for one year using live camera footage from six zoos across the world. Our results indicate that life stage was associated with changes in overall activity, feeding, locomotion, and pacing, and that sex influenced scent anointing and anogenital rubbing. Overall, the circadian rhythms showed three peaks of activity, including a nocturnal peak, as seen in wild giant pandas. We also found associations between sexual-related, stereotypical/abnormal, and feeding behavior, which are possibly linked to the timing of migration of wild pandas, and elucidated the relationship between a mother and cub, finding that they concentrate maternal behaviors to mainly after closing hours. Understanding these cycle patterns can aid animal care staff in predicting changing needs throughout the day, year, and life cycle and preemptively provide for those needs to best avoid welfare concerns.

The development of laying hen locomotion in 3D space is affected by early environmental complexity and genetic strain

Adult laying hens are increasingly housed in spatially complex systems, e.g., non-cage aviaries, where locomotion between elevated structures can be challenging for these gallinaceous birds. This study assessed the effect of early environmental complexity on spatial skills in two genetic strains. Brown (B) and white (W) feathered birds were raised in: Conventional cages with minimal complexity (Conv) or rearing aviaries with low (Low), intermediate (Mid), or high complexity (High). Birds from each housing treatment were challenged at three different time points in three different, age-appropriate vertical spatial tasks. Whites performed better than brown birds in all tests regardless of rearing environment. In chicks, test performance was predominantly explained by variation between replicates and differences in motivation for test participation. Treatment effects were seen in pubertal birds (pullets), with pullets from aviaries performing better than those from Conv. White High pullets performed better than white Mid or Low, an effect that was not found in browns. Pullets preferred to use a ramp to move downwards, but only when ramps had previously been experienced and when the ramp was not too steep. Overall, early environmental complexity affected spatial skills of laying hen pullets with stronger effects in white than brown feathered birds.

Domestication and social environment modulate fear responses in young chickens

Domesticated species differ from their wild ancestors in a mosaic of traits. Classical domestication theories agree that reactivity to fear and stress is one of the main traits affected. Domesticated species are expected to be less fear and stress prone to than their wild counterparts. To test this hypothesis, we compared the behavioural responses of White Leghorn (WL) chicks to their wild counterparts, Red Junglefowl (RJF) chicks in risk-taking situations. In order to obtain food, the chicks faced an unknown and potentially harmful object at the presence or absence of a social partner. We found that according to our predictions, RJF were more stressed and fearful of the object than the WL. Still, RJF were more explorative than WL. Additionally, the presence of a social partner reduced the fear response in both, but had a stronger effect on RJF. Finally, WL were more food orientated than the RJF. Our results confirmed classical domestication hypotheses of downregulation of the stress system and importance of the social partner in domesticated farm chicken.

Differences among domestic chicken breeds in tonic immobility responses as a measure of fearfulness

Background

One priority for animal welfare is for animals to experience less fear, especially during human contact. For domestic animals, breeds that are less fearful may provide genetic resources to develop strains with improved welfare due to lower susceptibility to fear. Genetic predispositions inherited in these breeds might reflect the large diversity of chicken breeds. The goal of the present study was to systematically test a diverse group of chicken breeds to search for breeds that experience less fear.

Methods

Nineteen chicken breeds from commercial hybrid lines, native layer-type, meat-type and dual-purpose breeds, ornamental breeds as well as bantam breeds were tested in a standardized tonic immobility (TI) test. Chickens were manually restrained on their back, and the time to first head movement and first leg movement, the duration of TI, as well as the number of attempts needed to induce TI were measured.

Results

The TI response differed among chicken breeds (p ≤ 0.001) for naïve, mature hens. The median number of attempts required to induce TI ranged from 1 to 2 and did not differ significantly among breeds. Median durations were much more variable, with Lohmann Brown showing shortest durations (6 s, 12 s, 58 s for time to first head movement, first leg movement and total duration of TI, respectively). In contrast, medians reached the maximum of 600 s for all three measures in German Creepers. Repeated tests on the same individuals did not affect attempts needed to induce TI nor TI durations. Breeds clustered into two main groups, with layer-type native breeds and ornamental breeds having longer TI durations, and bantam, dual-purpose and meat-type native breeds having shorter TI durations.

Conclusions

Our findings provide evidence for substantial variation of fearfulness among breeds. This variation could be linked to the intended use during the breed's specific history. Knowledge and quantitative measurement of these behavioural responses provide the opportunity to improve welfare through selection and future breeding.

Fearfulness in Commercial Laying Hens: A Meta-Analysis Comparing Brown and White Egg Layers

High fearfulness in commercial laying hens can negatively affect production parameters and animal welfare. Brown and white egg layers differ in several behavioral characteristics, though reported differences in fearfulness are inconsistent. A meta-analysis was conducted to determine whether there are systematic differences in measures of fearfulness between brown and white layers. Twenty-three studies that examined either 1 or both of 2 behavioral tests were included: tonic immobility (TI) (longer duration = higher fearfulness, 16 studies) and novel object (NO) test (lower approach rate = higher fearfulness, 11 studies). The 2 tests were analyzed separately. TI analyses: A generalized linear mixed effect model (GLMM) with a lognormal distribution was fitted to describe the data with experiment nested in study as a random effect. Explanatory (X) variables were considered through backward selection, where potential X-variables included color (brown vs. white layers), decade (1980s, 2000s, 2020s), age (prelay vs. in lay), genetic stock (hybrid vs. grand-/parent stock), and methodology (back vs. side position). NO test analyses: univariable GLMMs with a beta distribution were fitted with approach rate as the Y-variable and color, decade, age, stock, or 2 methodological factors (test duration, single vs. group testing) as X-variables. Models were evaluated by assessing information criteria, residuals/random effect normality, significance of X-variables and model evaluation statistics (mean square prediction error, concordance correlation coefficient). TI duration was best explained by a color-by-decade interaction (P = 0.0006). Whites in the 1980s had longer TI durations (709.43 ± 143.88 s) than browns in the 1980s (282.90 ± 59.70 s), as well as in comparison to browns (208.80 ± 50.82 s) or whites (204.85 ± 49.60 s) in the 2020s. The NO approach rate was best explained by color (P ≤ 0.05 in 3 models), age (P < 0.05 in 3 models), and decade (P = 0.04). Whites had a higher approach rate (0.7 ± 0.07) than browns (0.5 ± 0.11), birds in lay a higher rate (0.8 ± 0.07) than birds prelay (0.4 ± 0.12), and approach rate for papers published in the 2000s (0.8 ± 0.09) was higher than in the 2020s (0.2 ± 0.12). The phylogenetic difference in the 1980s was no longer detectable after enforcing an upper limit on TI durations (10 min), as became common practice in later studies. Our findings suggest that phylogenetic differences in fearfulness and changes over time are test dependent, and this raises important questions and potential consequences for assessing hen welfare in commercial egg production.

Contrafreeloading and foraging-related behavior in hens differing in laying performance and phylogenetic origin

Different breeds of domestic and junglefowl differ in foraging strategies indicating that domestication resulted in modified energy saving behavioral strategies. In the present study we investigated foraging strategies and foraging-related behavior in 4 lines of laying hens differing in phylogenetic origin and laying performance to analyze a possible relationship between foraging and the level of egg production. High performing brown and white pure bred lines were compared with their low performing brown and white counterparts. To control possible effects on behavior other than genetic effects, all hens were reared and kept in an identical environment. A total of 72 hens from each line were kept in 6 compartments with 12 hens per compartment, respectively. Observations were done for 3 times during one laying period. Foraging strategy was tested by a contrafreeloading (CFL) paradigm. CFL describes a behavior in which animals prefer food that requires effort to obtain, although at the same time food is freely available. The hens were offered a commercial standard diet in one trough and a mixture of wood shavings and commercial standard diet in another trough. The behavior of hens was video recorded and the activity level of individual hens in the litter area was recorded by an antenna-transponder system. The high performing layers showed less CFL and foraging-related behavior compared with their low performing counterparts in both the white and brown layers. Despite differences in CFL, all hens showed a preference for the commercial standard diet compared to the mixture of wood-shavings. Our results show an association between foraging strategy and level of egg production. This suggests that a high level of egg production is accompanied by behaviors enabling the hens to satisfy their higher energy demand more efficiently. Saving energy by reduced activity probably allows them to reallocate energy into reproduction, that is, laying performance.

Commercial layer hybrids kept under organic conditions: a comparison of range use, welfare and egg production in two layer strains

Outdoor range areas provide laying hens with improved opportunities to perform natural behaviors and increase the available space per bird, however, birds are also exposed to potentially stressful factors including weather and predators. Ability to cope with challenging environments varies between different strains and must be considered to ensure good welfare. The aim of this study was to determine how suitable 2 hybrids, the Dekalb White (DW) and the Bovans Brown (BB), are for organic production with special emphasis on ranging behavior. A total of 1,200 hens were housed according to organic regulations across 12 flocks of 100 birds. Range and shelter use, effect of weather, vegetation cover, egg production and quality, and mortality were assessed in addition to a range of clinical welfare indicators. Initially a greater proportion of DW hens accessed the range. However, after approximately 2 mo, a greater proportion of BB were using the range and venturing further from the house. DW hens were more likely to use the shelters than BB hens (P < 0.001). Vegetation was also worn away to a greater extent in the BB ranges. Weather affected the proportion of hens that went outside, the distance ranged from the popholes, and shelter use. BB hens were found to have better plumage condition (P < 0.001), fewer footpad lesions (P < 0.001), fewer comb wounds (P < 0.001), and lower mortality rates (P = 0.013). Both hybrids experienced keel bone fractures, though DW hens had more at the cranial portion (P < 0.001) and BB at the caudal portion (P < 0.001). DW hens had an earlier onset of lay and higher egg production than BB hens (P < 0.001), though BB hens laid heavier eggs (P < 0.001) with thicker shells (P = 0.001). Overall, BB hens seemed to perform superiorly or equivalently to the DW hens for all variables apart from egg production. These results demonstrate the importance of considering the strain of bird selected for organic production systems in order for the birds to reap the potential benefits that are offered by outdoor access.

The Welfare Status of Hens in Different Housing Systems – A Review

The currently used poultry farming methods, which aim to maximise economic profit, are based on ever new technological solutions that improve flock management and increase bird performance. However, they do not always meet the natural needs of birds. Every housing method and technological solution currently in use is faced with some issues, such as social stress, adverse temperature/ humidity conditions, risk of zoonoses, and behavioural pathologies, which determine poultry performance and welfare. Disregard for animal welfare involves not only ethical but also practical aspects, because well-being and housing comfort translate into better weight gains, health and productivity of the birds. The studies reported here suggest that every production system, despite the many welfare-improving aspects, causes numerous behavioural, productivity and health abnormalities in laying hens. Therefore, further research is needed to identify various risk factors for the purpose of improving housing systems and increasing the welfare of hens.

Keel Bone Damage in Laying Hens-Its Relation to Bone Mineral Density, Body Growth Rate and Laying Performance

Simple Summary

Keel bone damage is an important welfare issue for laying hens. Four lines of laying hens, differing in phylogenetic origin and laying rate kept in single cages or a floor housing system were weighed and deformities of the keel bone were evaluated regularly between 15 and 69 weeks of age. Deformities, fractures and the bone mineral density of the keels were assessed after hens were euthanized. We analyzed the relationship between bone mineral density and total egg number as well as body growth. Hens kept in cages showed more deformities, but fewer fractures and a lower bone mineral density of the keel bone than did floor-housed hens. Keel bones of white-egg layers had a lower mineral density and were more often deformed compared with brown-egg layers. Keel bones were more often broken in hens of the layer lines with a high laying rate compared to the lines with a moderate laying rate. Laying rate and adult body weight had an effect on the keel bone mineral density. The study contributes to the understanding of factors causing keel bone damage in laying hens. It showed that the bone mineral density greatly affects keel bone deformities.

Abstract

Keel bone damage is an important animal welfare problem in laying hens. Two generations of four layer lines, differing in phylogenetic background and performance level and kept in single cages or floor pens were weighed and scored for keel bone deformities (KBD) during the laying period. KBD, keel bone fractures (KBF) and the bone mineral density (BMD) of the keels were assessed post mortem. For BMD, relationships to laying performance and body growth were estimated. Caged hens showed more deformities, but fewer fractures and a lower BMD of the keel bone than floor-housed hens. White-egg layers had a lower BMD (0.140–0.165 g/cm²) and more KBD than brown-egg layers (0.179–0.184 g/cm²). KBF occurred more often in the high-performing lines than the moderate-performing ones. However, in the high-performing lines, BMD was positively related to total egg number from 18 to 29 weeks of age. The adult body weight derived from fitted growth curves (Gompertz function) had a significant effect (p < 0.001) on keels’ BMD. The study contributes to the understanding of predisposing factors for keel bone damage in laying hens. It showed that the growth rate has a rather subordinate effect on keels’ BMD, while the BMD itself greatly affects KBD.

Influence of Age and Phylogenetic Background on Blood Parameters Associated With Bone Metabolism in Laying Hens

The high laying performance of today’s laying hens places enormous demands on their mineral metabolism. While up-to-date data are rare, the present study aimed to describe blood parameters associated with egg laying and bone metabolism during the pre-laying period, in the course of the laying period and the daily egg laying cycle. Ten to 15 laying hens of two high-performing, phylogenetically divergent lines (BLA: brown-egg layer; WLA: white-egg layer), kept in single cages were blood sampled at 17, 25, 29, 49, and 69 weeks of age. Sampling was made at 6 a.m., 10 a.m., 2 p.m. and, with the exception of week 17, 6 p.m. Blood samples were analyzed for concentrations of total and ionized calcium, inorganic phosphate (PO4), markers of bone formation (osteocalcin) and resorption [carboxyterminal crosslinked telopeptide of type I collagen (CTX-I)], 25-hydroxycholecalciferol (25(OH)D₃) and estradiol-17β. In the pre-laying period (17 week), the estradiol-17β level calculated for WLA was more than twice as high as the level calculated for BLA, while no significant difference could be observed in the laying period (25 to 69 weeks). BLA hens had significantly higher total calcium concentrations at 49 weeks of age as well as up to twice as high levels of osteocalcin and 25(OH)D₃ than WLA at any time of the day from 25 to 69 weeks of age. While osteocalcin, CTX-I and 25(OH)D₃ concentrations were significantly higher before the onset of lay, total calcium and estradiol-17β levels significantly increased from 17 to 69 weeks of age. In contrast, PO4 values varied only slightly during the experimental period and ionized calcium was highest at 17 and 49 weeks of age and lowest around peak production (29 week). In the course of the daily egg laying cycle blood concentrations clearly reflected the stage of egg formation. Our results provide up-to-date data of bone- and egg laying-associated blood parameters of two contemporary purebred layer lines over the course of the pre- and egg-laying period and the daily egg laying cycle. Differences between brown- and white-egg layers raise questions, whether phylogenetic background determines their efficiency to cope with high calcium demands relating to egg production.

Behavioural consequences of divergent selection on general locomotor activity in chickens

General locomotor activity is a highly variable phenotypic trait of animals. In domestic chickens it is different within and between breeds. The general locomotor activity is a substantially heritable trait and has been shown to be correlated with several other behavioural traits, such as for example feather pecking and anxiety in chickens. However, whether there is a relation between different levels of general locomotor activity and behavioural changes remained unclear. Therefore, a selection line model system has been established, where hens from the same founder population were selected over eight generations for either high or low general locomotor activity. The selection led to significant increases, respectively decreases in general locomotor activity and differences in growth. We here tested 128 hens of the 8^th generation in three behavioural tests. We assumed fearfulness to be affected from selection on general locomotor activity, which we tested in a tonic immobility test. Socio-positive and socio-negative behaviours were tested in respective test paradigms. Fearfulness was higher in hens selected for high general locomotor activity. Social behavioural traits and feather pecking were not affected by selection for general locomotor activity. Evolutionary mechanisms that link fear and general locomotor activity are discussed and also why social behaviours and feather pecking seems not to be affected from selection on general locomotor activity. Our results provide interesting new insights on how selection on one trait, general locomotor activity, affects the behavioural phenotype in other dimensions too.

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

Both genetic background and maternal care can have a strong influence on cognitive and emotional development. To investigate these effects and their possible interaction, White Leghorn (LH) and Brown Nick (BN) chicks, two hybrid lines of layer hen commonly used commercially, were housed either with or without a mother hen in their first five weeks of life. From three weeks of age, the chicks were tested in a series of experiments to deduce the effects of breed and maternal care on their fear response, foraging and social motivation, and cognitive abilities. The LH were found to explore more and showed more attempts to reinstate social contact than BN. The BN were less active in all tests and less motivated than LH by social contact or by foraging opportunity. No hybrid differences were found in cognitive performance in the holeboard task. In general, the presence of a mother hen had unexpectedly little effect on behavior in both LH and BN chicks. It is hypothesized that hens from commercially used genetic backgrounds may have been inadvertently selected to be less responsive to maternal care than ancestral or non-commercial breeds. The consistent and strong behavioral differences between genetic strains highlights the importance of breed-specific welfare management processes.

Fear but not social behaviour is affected by a polymorphism in the 5'-flanking region of the serotonin transporter (5-HTT) gene in adult hens

The serotonin transporter gene (5-HTT) is involved in the regulation of the neural serotonin. Polymorphisms in the 5-HTT gene have been described in many species to be involved in physiological processes and emotions. A functional polymorphism in the 5´-flanking region of the 5-HTT gene is known from chickens, with a deletion-allele (D), which is associated with an increased 5-HTT expression, in comparison to the wild-type-allele (W). In domestic populations, the majority of hens carry the W-allele. The regulatory changes of the 5-HTT are accompanied in chickens, as in humans, by modulations of fear. Beside these effects on fear, the understanding of potential functional consequences on the social behaviour in the gregarious chicken is lacking. Thus, we here investigated whether the 5-HTT polymorphism with three genotypes (WW, WD, DD), is not only linked to fear-related behaviour, but affects also socio-positive and -negative behaviours of adult hens. Our data confirmed the effects on fear-related behaviour. WW hens showed highest levels of fear. Interestingly, no differences in the social behaviours were present between the hens of the different 5-HTT genotypes. We further discuss implications for potential evolutionary pathways via natural selection and / or artificial selection through domestication of the 5-HTT polymorphism, which might have enabled a stable social lifestyle in the wild ancestors of modern chickens.

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

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 (Chi2 3 = 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.