Malfunctioned inflammatory response and serotonin metabolism at the microbiota-gut-brain axis drive feather pecking behavior in laying hens

Feather pecking (FP) is a multifactorial abnormal behavior in laying hens where they display harmful pecks in conspecifics. FP has been associated with the altered functioning of the microbiome-gut-brain axis affecting host emotions and social behavior. The altered levels of serotonin (5-HT), a key monoaminergic neurotransmitter at both terminals of the gut-brain axis, affect the development of abnormal behavior, such as FP in laying hens. However, the underlying mechanism involving reciprocal interactions along the microbiota-gut-brain axis, particularly about the metabolism of 5-HT, remains unclear in FP phenotypes. This study examined the microbiota diversity, intestinal microbial metabolites, inflammatory responses, and 5-HT metabolism in divergently selected high (HFP; n = 8) and low (LFP; n = 8) FP hens to investigate the possible interconnections between FP behavior and the examined parameters. The 16S rRNA analysis revealed that compared to LFP birds, the gut microbiota of HFP birds exhibited a decrease in the abundance of phylum Firmicutes and genera Lactobacillus, while an increase in the abundance of phylum Proteobacteria and genera Escherichia Shigella and Desulfovibrio. Furthermore, the intestinal differential metabolites associated with FP phenotypes were mainly enriched in the tryptophan metabolic pathway. HFP birds had higher tryptophan metabolites and possibly a more responsive immune system compared to the LFP birds. This was indirectly supported by altered TNF-α levels in the serum and expression of inflammatory factor in the gut and brain. Moreover, HFP birds had lower serum levels of tryptophan and 5-HT compared to LFP birds, which was consistent with the downregulation of 5-HT metabolism-related genes in the brain of HFP birds. The correlation analysis revealed that genera Lactobacillus and Desulfovibrio were associated with differences in intestinal metabolites, 5-HT metabolism, and inflammatory response between the LFP and HFP birds. In conclusion, differences in the cecal microbiota profile, immune response and 5-HT metabolism drive FP phenotypes, which could be associated with the gut abundance of genera Lactobacillus and Desulfovibrio.

Structural variation and eQTL analysis in two experimental populations of chickens divergently selected for feather-pecking behavior

Feather pecking (FP) is a damaging nonaggressive behavior in laying hens with a heritable component. Its occurrence has been linked to the immune system, the circadian clock, and foraging behavior. Furthermore, dysregulation of miRNA biogenesis, disturbance of the gamma-aminobutyric acid (GABAergic) system, as well as neurodevelopmental deficiencies are currently under debate as factors influencing the propensity for FP behavior. Past studies, which focused on the dissection of the genetic factors involved in FP, relied on single nucleotide polymorphisms (SNPs) and short insertions and deletions < 50 bp (InDels). These variant classes only represent a certain fraction of the genetic variation of an organism. Hence, we reanalyzed whole-genome sequencing data from two experimental populations, which have been divergently selected for FP behavior for over more than 15 generations, performed variant calling for structural variants (SVs) as well as tandem repeats (TRs), and jointly analyzed the data with SNPs and InDels. Genotype imputation and subsequent genome-wide association studies, in combination with expression quantitative trait loci analysis, led to the discovery of multiple variants influencing the GABAergic system. These include a significantly associated TR downstream of the GABA receptor subunit beta-3 (GABRB3) gene, two microRNAs targeting several GABA receptor genes, and dystrophin (DMD), a direct regulator of GABA receptor clustering. Furthermore, we found the transcription factor ETV1 to be associated with the differential expression of 23 genes, which points toward a role of ETV1, together with SMAD4 and KLF14, in the disturbed neurodevelopment of high-feather pecking chickens.

The Relationships between Damaging Behaviours and Health in Laying Hens

Simple Summary

The design of housing systems and genetic selection of laying hens have in the past focused mainly on productivity, excluding issues around the animals’ behavioural needs and welfare. Because of inadequate housing conditions and especially a barren environment, behavioural disorders such as feather and body pecking, as well as cannibalism, occur in the modern layer industry. Since conventional cages for egg production were banned in the European Union in January 2012, alternative systems such as floor, aviary, free-range, and organic systems have become increasingly common and now concern over 50% of hens housed in Europe. Despite the many advantages that come with non-cage systems, the shift to a housing system where laying hens are kept in larger groups and more complex environments has given rise to new challenges related to management, health, and welfare. We have carried out a review showing the close relationships between damaging behaviours and health in modern husbandry systems for laying hens.

Abstract

Since the ban in January 2012 of conventional cages for egg production in the European Union (Council Directive 1999/74/EC), alternative systems such as floor, aviary, free-range, and organic systems have become increasingly common, reaching 50% of housing for hens in 2019. Despite the many advantages associated with non-cage systems, the shift to a housing system where laying hens are kept in larger groups and more complex environments has given rise to new challenges related to management, health, and welfare. This review examines the close relationships between damaging behaviours and health in modern husbandry systems for laying hens. These new housing conditions increase social interactions between animals. In cases of suboptimal rearing and/or housing and management conditions, damaging behaviour or infectious diseases are likely to spread to the whole flock. Additionally, health issues, and therefore stimulation of the immune system, may lead to the development of damaging behaviours, which in turn may result in impaired body conditions, leading to health and welfare issues. This raises the need to monitor both behaviour and health of laying hens in order to intervene as quickly as possible to preserve both the welfare and health of the animals.

The light response in chickens divergently selected for feather pecking behavior reveals mechanistic insights towards psychiatric disorders

Background

Feather pecking is a serious behavioral disorder in chickens that has a considerable impact on animal welfare and poses an economic burden for poultry farming. To study the underlying genetics of feather pecking animals were divergently selected for feather pecking over 15 generations based on estimated breeding values for the behavior.

Methods and results

By characterizing the transcriptomes of whole brains isolated from high and low feather pecking chickens in response to light stimulation we discovered a putative dysregulation of micro RNA processing caused by a lack of Dicer1. This results in a prominent downregulation of the GABRB2 gene and other GABA receptor transcripts, which might cause a constant high level of excitation in the brains of high feather pecking chickens. Moreover, our results point towards an increase in immune system-related transcripts that may be caused by higher interferon concentrations due to Dicer1 downregulation.

Conclusion

Based on our results, we conclude that feather pecking in chickens and schizophrenia in humans have numerous common features. For instance, a Dicer1 dependent disruption of miRNA biogenesis and the lack of GABRB2 expression have been linked to schizophrenia pathogenesis. Furthermore, disturbed circadian rhythms and dysregulation of genes involved in the immune system are common features of both conditions.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11033-021-07111-4.

L. rhamnosus improves the immune response and tryptophan catabolism in laying hen pullets

In mammals, early-life probiotic supplementation is a promising tool for preventing unfavourable, gut microbiome-related behavioural, immunological, and aromatic amino acid alterations later in life. In laying hens, feather-pecking behaviour is proposed to be a consequence of gut-brain axis dysregulation. Lactobacillus rhamnosus decreases stress-induced severe feather pecking in adult hens, but whether its effect in pullets is more robust is unknown. Consequently, we investigated whether early-life, oral supplementation with a single Lactobacillus rhamnosus strain can prevent stress-induced feather-pecking behaviour in chickens. To this end, we monitored both the short- and long-term effects of the probiotic supplement on behaviour and related physiological parameters. We hypothesized that L. rhamnosus would reduce pecking behaviour by modulating the biological pathways associated with this detrimental behaviour, namely aromatic amino acid turnover linked to neurotransmitter production and stress-related immune responses. We report that stress decreased the proportion of cytotoxic T cells in the tonsils (P = 0.047). Counteracting this T cell depression, birds receiving the L. rhamnosus supplementation significantly increased all T lymphocyte subset proportions (P < 0.05). Both phenotypic and genotypic feather peckers had lower plasma tryptophan concentrations compared to their non-pecking counterparts. The probiotic supplement caused a short-term increase in plasma tryptophan (P < 0.001) and the TRP:(PHE + TYR) ratio (P < 0.001). The administration of stressors did not significantly increase feather pecking in pullets, an observation consistent with the age-dependent onset of pecking behaviour. Despite minimal changes to behaviour, our data demonstrate the impact of L. rhamnosus supplementation on the immune system and the turnover of the serotonin precursor tryptophan. Our findings indicate that L. rhamnosus exerts a transient, beneficial effect on the immune response and tryptophan catabolism in pullets.

Causes of feather pecking and subsequent welfare issues for the laying hen: a review

When feather-pecking behaviour by hens becomes repetitive, plumage damage often results for the recipient of the pecks. The forceful removal of feathers and vigorous pecks directed at the skin may also cause pain, fear and even wounds. ‘Outbreaks’ of pecking behaviour have been reported in all housing systems in which poultry are managed. Pecking may progress to cannibalism and death, thus constituting significant hen welfare and farm economy problems. Farmers apply preventative management practices to minimise the risk of outbreaks. However, outbreaks are unpredictable and, once in progress, are difficult to control, especially in non-cage housing systems. For more than a century, research has been directed at trying to identify the causal factors underlying this problem, without success. The problem is multi-factorial and different studies often identify contradictory findings, such as, for example, in relation to the effects of adding forage to increase environmental enrichment, among others. The present review aims to provide background information about severe feather-pecking behaviour in laying hens, with mention of the resultant issues from repeated performance, such as, for example, on feather cover over the life of the laying hen. On-farm surveys, epidemiological studies and experimental trials have generated much information that has improved our general understanding of the significance of the problem, even though studies have typically been inconclusive due to its multi-factorial causes. While ‘Good Practice Guides’ are available and provide relevant advice for farmers to manage flocks to minimise the risk of outbreaks, we suggest significant progress towards identifying the root-cause(s) of the problem will more likely be achieved through controlled experimental trials using research models than through survey approaches. For example, using a stress-induction model, researchers should first focus on the impact of cumulative stressors in the flock that seem to predispose a hen to either become a feather pecker, or be the victim of pecking. Subsequent research should then investigate the affected hens for altered behavioural or (neuro-) physiological states, or physical stimuli on the skin and feathers, that may increase the motivation of hens to become feather peckers.

Analysis of the brain transcriptome in lines of laying hens divergently selected for feather pecking

Background

Feather pecking (FP) in laying hens reduces animal welfare and leads to economic losses for the layer industry. FP is considered a heritable condition that is influenced by dysregulation of neurotransmitter homeostasis, the gut microbiome, and the immune system. To identify genes and biological pathways responsible for FP behavior we compared the brain transcriptomes of 48 hens divergently selected for FP. In addition, we tested if high feather peckers (HFP) and low feather peckers (LFP) respond differently to light since light has been shown to trigger FP behavior.

Results

Of approximately 48 million reads/sample an average of 98.4% were mapped to the chicken genome (GRCg6a). We found 13,070 expressed genes in the analyzed brains of which 423 showed differential expression between HFP and LFP. Genes of uncertain function and non-coding RNAs were overrepresented among those transcripts. Functional analyses revealed the involvement of cholinergic signaling, postsynaptic activity, membrane channels, and the immune system. After the light stimulus, 28 genes were found to be differentially expressed. These included an interaction cluster of core components of the circadian clock. However, differences in the response to light between HFP and LFP were not detectable.

Conclusions

Genes involved in cholinergic signaling, channel activity, synaptic transmission, and immune response were found to be involved in FP behavior. We propose a model in which the gut microbiota modulates the immune system, which in turn affects cholinergic signaling. This might have an influence on monoamine signaling with possible involvement of GABA or glutamate signaling.

Omics Application in Animal Science-A Special Emphasis on Stress Response and Damaging Behaviour in Pigs

Increasing stress resilience of livestock is important for ethical and profitable meat and dairy production. Susceptibility to stress can entail damaging behaviours, a common problem in pig production. Breeding animals with increased stress resilience is difficult for various reasons. First, studies on neuroendocrine and behavioural stress responses in farm animals are scarce, as it is difficult to record adequate phenotypes under field conditions. Second, damaging behaviours and stress susceptibility are complex traits, and their biology is not yet well understood. Dissecting complex traits into biologically better defined, heritable and easily measurable proxy traits and developing biomarkers will facilitate recording these traits in large numbers. High-throughput molecular technologies (“omics”) study the entirety of molecules and their interactions in a single analysis step. They can help to decipher the contributions of different physiological systems and identify candidate molecules that are representative of different physiological pathways. Here, we provide a general overview of different omics approaches and we give examples of how these techniques could be applied to discover biomarkers. We discuss the genetic dissection of the stress response by different omics techniques and we provide examples and outline potential applications of omics tools to understand and prevent outbreaks of damaging behaviours.

Chicken lines divergently selected on feather pecking differ in immune characteristics

It is crucial to identify whether relations between immune characteristics and damaging behaviors in production animals exist, as these behaviors reduce animal welfare and productivity. Feather pecking (FP) is a damaging behavior in chickens, which involves hens pecking and pulling at feathers of conspecifics. To further identify relationships between the immune system and FP we characterized high FP (HFP) and low FP (LFP) selection lines with regard to nitric oxide (NO) production by monocytes, specific antibody (SpAb) titers, natural (auto)antibody (N(A)Ab) titers and immune cell subsets. NO production by monocytes was measured as indicator for innate pro-inflammatory immune functioning, SpAb titers were measured as part of the adaptive immune system and N(A)Ab titers were measured as they play an essential role in both innate and adaptive immunity. Immune cell subsets were measured to identify whether differences in immune characteristics were reflected by differences in the relative abundance of immune cell subsets. Divergent selection on FP affected NO production by monocytes, SpAb and N(A)Ab titers, but did not affect immune cell subsets. The HFP line showed higher NO production by monocytes and higher IgG N(A)Ab titers compared to the LFP line. Furthermore the HFP line tended to have lower IgM NAAb titers, but higher IgM and IgG SpAb titers compared to the LFP line. Thus, divergent selection on FP affects the innate and adaptive immune system, where the HFP line seems to have a more responsive immune system compared to the LFP line. Although causation cannot be established in the present study, it is clear that relationships between the immune system and FP exist. Therefore, it is important to take these relationships into account when selecting on behavioral or immunological traits.

Influence of the microbiota-gut-brain axis on behavior and welfare in farm animals: A review

There is increasing evidence of a pivotal role of the gut microbiota (GUT-M) in key physiological functions in vertebrates. Many studies discuss functional implications of the GUT-M not only on immunity, growth, metabolism, but also on brain development and behavior. However, while the influence of the microbiota-gut-brain axis (MGBA) on behavior is documented in rodents and humans, data on farm animals are scarce. This review will first report the well-known influence of the MGBA on behavior in rodent and human and then describe its influence on emotion, memory, social and feeding behaviors in farm animals. This corpus of experiments suggests that a better understanding of the effects of the MGBA on behavior could have large implications in various fields of animal production. Specifically, animal welfare and health could be improved by selection, nutrition and management processes that take into account the role of the GUT-M in behavior.

Review of Sensor Technologies in Animal Breeding: Phenotyping Behaviors of Laying Hens to Select Against Feather Pecking

Simple Summary

The European Cooperation in Science and Technology (COST) Action GroupHouseNet aims to provide synergy among scientists to prevent damaging behavior in group-housed pigs and laying hens. One goal of this network is to determine how genetic and genomic tools can be used to breed animals that are less likely to perform damaging behavior on their pen-mates. In this review, the focus is on feather-pecking behavior in laying hens. Reducing feather pecking in large groups of hens is a challenge, because it is difficult to identify and monitor individual birds. However, current developments in sensor technologies and animal breeding have the potential to identify individual animals, monitor individual behavior, and link this information back to the underlying genotype. We describe a combination of sensor technologies and “-omics” approaches that could be used to select against feather-pecking behavior in laying hens.

Abstract

Damaging behaviors, like feather pecking (FP), have large economic and welfare consequences in the commercial laying hen industry. Selective breeding can be used to obtain animals that are less likely to perform damaging behavior on their pen-mates. However, with the growing tendency to keep birds in large groups, identifying specific birds that are performing or receiving FP is difficult. With current developments in sensor technologies, it may now be possible to identify laying hens in large groups that show less FP behavior and select them for breeding. We propose using a combination of sensor technology and genomic methods to identify feather peckers and victims in groups. In this review, we will describe the use of “-omics” approaches to understand FP and give an overview of sensor technologies that can be used for animal monitoring, such as ultra-wideband, radio frequency identification, and computer vision. We will then discuss the identification of indicator traits from both sensor technologies and genomics approaches that can be used to select animals for breeding against damaging behavior.

Stress response, peripheral serotonin and natural antibodies in feather pecking genotypes and phenotypes and their relation with coping style

Feather pecking (FP), a serious welfare and economic issue in the egg production industry, has been related to coping style. Proactive and reactive coping styles differ in, among others, the stress response, serotonergic activity and immune activity. Yet, it is unknown whether genetic lines divergently selected on FP (i.e. FP genotypes) or individuals differing in FP (i.e. FP phenotypes) can be categorized into coping styles. Therefore, we determined peripheral serotonin (5-HT) levels, natural antibody (NAb) titers, behavioral and corticosterone (CORT) responses to manual restraint (MR) in FP genotypes (high FP (HFP), low FP (LFP) and unselected control (CON) line) and FP phenotypes (feather pecker, feather pecker-victim, victim and neutral). We further examined the consistency of and relationships between behavioral and physiological measures. FP genotypes differed in behavioral responses to MR, 5-HT levels and NAb titers, but not in CORT levels after MR. HFP birds had less active responses at adolescent age, but more active responses at adult age compared to LFP and CON birds. The CON line had higher 5-HT levels at adolescent age, while the HFP line had lower 5-HT levels than the other lines at adult age. Overall, the HFP line had lower IgM NAb titers, while the LFP line had lower IgG NAb titers compared to the other lines. FP phenotypes differed in behavioral responses to MR and 5-HT levels, but not in CORT levels after MR or NAb titers. Within the HFP line, feather peckers tended to have less active responses compared to neutrals at adolescent age, while victims had more active responses compared to the other phenotypes at adult age. Feather peckers had higher 5-HT levels than neutrals at adult age. Behavioral and CORT responses to MR were not consistent over time, suggesting that responses to MR might not reflect coping style in this study. Furthermore, proactive behavioral responses were correlated with reactive physiological measures and vice versa. Thus, it was not possible to categorize FP genotypes or FP phenotypes into specific coping styles.

Enhanced Expression of Serotonin Receptor 5-Hydroxytryptamine 2C is Associated with Increased Feather Damage in Dongxiang Blue-Shelled Layers

The gene encoding the serotonin receptor 5-hydroxytraptamine 2C (HTR2C) has been implicated in behavioral phenotypes in a number of species. In previous studies, a mutation in the chicken HTR2C gene was found to be associated with feather condition, thereby suggesting a relationship between the gene and receiving feather pecking activity. The present study analyzed the chicken HTR2C gene at both the genomic make-up and expression level in Dongxiang blue-shelled layer. A significant association between the single nucleotide polymorphism (SNP) rs13640917 (C/T) and feather condition was confirmed in the Chinese local layer. Enhanced HTR2C gene expression (151.1-fold) that was associated with high feather damage indicated that the right cerebrum might be the critical region for HTR2C to participate in the regulation of receiving feather pecking behavior.

The presence of extreme feather peckers in groups of laying hens

Feather pecking is a serious economic and welfare problem in laying hens. Feather damage occurs mainly through severe feather pecking (SFP). Selection experiments have proved that this behavior is heritable and lines have been divergently selected for high (HFP) and low feather pecking (LFP). The number of bouts of SFP per hen follows a Poisson distribution with a maximum nearby 0. A few studies indicate that the distribution within flocks is not homogenous but contains sub-groups of birds showing extremely high levels of feather pecking (EFP). It was the aim of the current study to re-analyze data on SFP of lines selected for HFP/LFP and their F2 cross so as to uncover hidden sub-populations of EFP birds. Data of seven selection generations of HFP and LFP selection lines as well as their F2 cross have been used. We fitted a two-component mixture of Poisson distributions in order to separate the sub-group of EFP from the remaining birds. HFP and LFP lines differed mainly in mean bouts per bird. The proportion of EFP was only marginal in the LFP as compared with the HFP and the F2 population. Selection for LFP did not result in total elimination of EFP. The presence of even small proportions of EFP may play an important role in initiating outbreaks of feather pecking in large flocks. Further studies on feather pecking should pay special attention to the occurrence of EFP sub-groups.

Omnivores Going Astray: A Review and New Synthesis of Abnormal Behavior in Pigs and Laying Hens

Pigs and poultry are by far the most omnivorous of the domesticated farm animals and it is in their nature to be highly explorative. In the barren production environments, this motivation to explore can be expressed as abnormal oral manipulation directed toward pen mates. Tail biting (TB) in pigs and feather pecking (FP) in laying hens are examples of unwanted behaviors that are detrimental to the welfare of the animals. The aim of this review is to draw these two seemingly similar abnormalities together in a common framework, in order to seek underlying mechanisms and principles. Both TB and FP are affected by the physical and social environment, but not all individuals in a group express these behaviors and individual genetic and neurobiological characteristics play an important role. By synthesizing what is known about environmental and individual influences, we suggest a novel possible mechanism, common for pigs and poultry, involving the brain-gut-microbiota axis.

Developmental immune activation programs adult behavior: insight from research on birds

Immune activation early in life can program adult behavioral expression. Previous research on birds has documented effects of parasite exposure and immune challenges early in life on dispersal, song, personality, learning and feather pecking. However, the mechanisms responsible for mediating these programming effects are unknown. Candidate brain regions that may be most sensitive include the hippocampus and HVC. Without an understanding of mechanism, it is difficult to assess if programmed behaviors represent pathological side effects or behavioral modifications with benefits to either hosts or parasites. Future research on birds promises to provide novel insight into the adaptive value of programming effects of early life immune activation and the capacity for selection to buffer hosts against negative effects.

Relationships between range access as monitored by radio frequency identification technology, fearfulness, and plumage damage in free-range laying hens

Severe feather-pecking (SFP), a particularly injurious behaviour in laying hens (Gallus gallus domesticus), is thought to be negatively correlated with range use in free-range systems. In turn, range use is thought to be inversely associated with fearfulness, where fearful birds may be less likely to venture outside. However, very few experiments have investigated the proposed association between range use and fearfulness. This experiment investigated associations between range use (time spent outside), fearfulness, plumage damage, and BW. Two pens of 50 ISA Brown laying hens (n=100) were fitted with radio frequency identification (RFID) transponders (contained within silicone leg rings) at 26 weeks of age. Data were then collected over 13 days. A total of 95% of birds accessed the outdoor run more than once per day. Birds spent an average duration of 6.1 h outside each day over 11 visits per bird per day (51.5 min per visit). The top 15 and bottom 15 range users (n=30), as determined by the total time spent on the range over 13 days, were selected for study. These birds were tonic immobility (TI) tested at the end of the trial and were feather-scored and weighed after TI testing. Birds with longer TI durations spent less time outside (P=0.01). Plumage damage was not associated with range use (P=0.68). The small group sizes used in this experiment may have been conducive to the high numbers of birds utilising the outdoor range area. The RFID technology collected a large amount of data on range access in the tagged birds, and provides a potential means for quantitatively assessing range access in laying hens. The present findings indicate a negative association between fearfulness and range use. However, the proposed negative association between plumage damage and range use was not supported. The relationships between range use, fearfulness, and SFP warrant further research.

Integrated Genome-wide association and hypothalamus eQTL studies indicate a link between the circadian rhythm-related gene PER1 and coping behavior

Animal personality and coping styles are basic concepts for evaluating animal welfare. Struggling response of piglets in so-called backtests early in life reflects their coping strategy. Behavioral reactions of piglets in backtests have a moderate heritability, but their genetic basis largely remains unknown. Here, latency, duration and frequency of struggling attempts during one-minute backtests were repeatedly recorded of piglets at days 5, 12, 19, and 26. A genome-wide association study for backtest traits revealed 465 significant SNPs (FDR ≤ 0.05) mostly located in QTL (quantitative trait locus) regions on chromosome 3, 5, 12 and 16. In order to capture genes in these regions, 37 transcripts with significant SNPs were selected for expressionQTL analysis in the hypothalamus. Eight genes (ASGR1, CPAMD8, CTC1, FBXO39, IL19, LOC100511790, RAD51B, UBOX5) had cis- and five (RANGRF, PER1, PDZRN3, SH2D4B, LONP2) had trans-expressionQTL. In particular, for PER1, with known physiological implications for maintenance of circadian rhythms, a role in coping behavior was evidenced by confirmed association in an independent population. For CTC1 a cis-expression QTL and the consistent relationship of gene polymorphism, mRNA expression level and backtest traits promoted its link to coping style. GWAS and eQTL analyses uncovered positional and functional gene candidates for coping behavior.

Individual Consistency of Feather Pecking Behavior in Laying Hens: Once a Feather Pecker Always a Feather Pecker?

The pecking behavior [severe feather, gentle feather, and aggressive pecks (AP)] of individual White Shaver non-cage laying hens (n = 300) was examined at 21, 24, 27, 32, and 37 weeks. Hens were housed in 30 groups of 10 hens each and on 3 cm litter with access to a feeder, perch, and two nest boxes. The number of severe feather pecks given (SFPG) and received (SFPR) was used to categorize hens as feather peckers (P), victims (V), neutrals (N), or feather pecker-victims (PV) at each age. Hens categorized as PV exhibited pecking behaviors similar to P and received pecks similar to V. SFP given were correlated with APs given, but not with gentle feather pecks (GFP) given throughout the study. State-transition plot maps illustrated that 22.5% of P remained P, while 44% of PV remained PV throughout the duration of the study. Lifetime behavioral categories identified hens as a consistent feather pecker (5%), consistent neutral (3.9%), consistent victim (7.9%), consistent feather pecker-victim (29.4%), or inconsistent (53.8%) in their behavioral patterns throughout their life. Consistent feather peckers performed more SFP than hens of other categories, and consistent neutral hens received fewer GFP than consistent feather PV. No differences in corticosterone or whole blood serotonin levels were observed among the categories. Approximately, half of the population was classified as a feather pecker at least once during the study, while the remainder was never categorized as a feather pecker. Therefore, even if the development and cause of feather pecking may be multifactorial, once the behavior has been developed, some hens may persist in feather pecking. However, as some hens were observed to never receive or perform SFP, emphasis should be made to select for these hens in future breeding practices.

Effects of age at first access to range area on pecking behaviour and plumage quality of free-range layer chickens

Abstract. The aim of this study was to investigate the effects of age on pecking behaviour and plumage quality of free-range laying hens during first access to range. Six hundred 16-week-old layer pullets obtained from a commercial company were housed in a experimental free-range house. The experimental house consisted of a slat-and-litter floor with range area and was divided into three similar pens. The pullets were randomly assigned to a control and two experimental groups according to age at first access to range area. The birds were allowed into the range area for the first time at 18, 20 and 22 weeks of age in the groups of treatment I, treatment II and control, respectively. Pecking behaviour and plumage quality of the birds were measured for 8-week intervals from 24 to 48 weeks of age. Total feather damage significantly increased with age in all groups (P < 0.040, P < 0.006, P < 0.001). Compared to the control group, birds allowed into the range area earlier had less feather damage. The feather score of the tail body region in all groups was significantly greater (more damage) than in the others (P < 0.001). There were no significant differences for the total pecking behaviour of the birds in the groups at 24, 32, 40 and 48 weeks of age. Incidents of gentle feather pecking in every period were more frequent, while aggressive pecking was less frequent (P < 0.026, P < 0.007, P < 0.001). It can be said that access to range area as early as possible at the beginning of the laying period may be useful to reduce the negative effect of feather pecking in free-range layer chickens.

Tail biting in pigs: blood serotonin and fearfulness as pieces of the puzzle?

Tail biting in pigs is a widespread problem in intensive pig farming. The tendency to develop this damaging behaviour has been suggested to relate to serotonergic functioning and personality characteristics of pigs. We investigated whether tail biting in pigs can be associated with blood serotonin and with their behavioural and physiological responses to novelty. Pigs (n = 480) were born in conventional farrowing pens and after weaning at four weeks of age they were either housed barren (B) or in straw-enriched (E) pens. Individual pigs were exposed to a back test and novel environment test before weaning, and after weaning to a novel object (i.e. bucket) test in an unfamiliar arena. A Principal Component Analysis on behaviours during the tests and salivary cortisol (novel object test only) revealed five factors for both housing systems, labeled ‘Early life exploration’, ‘Near bucket’, ‘Cortisol’, ‘Vocalizations & standing alert’, and ‘Back test activity’. Blood samples were taken at 8, 9 and 22 weeks of age to determine blood platelet serotonin. In different phases of life, pigs were classified as tail biter/non-tail biter based on tail biting behaviour, and as victim/non-victim based on tail wounds. A combination of both classifications resulted in four pig types: biters, victims, biter/victims, and neutrals. Generally, only in phases of life during which pigs were classified as tail biters, they seemed to have lower blood platelet serotonin storage and higher blood platelet uptake velocities. Victims also seemed to have lower blood serotonin storage. Additionally, in B housing, tail biters seemed to consistently have lower scores of the factor ‘Near bucket’, possibly indicating a higher fearfulness in tail biters. Further research is needed to elucidate the nature of the relationship between peripheral 5-HT, fearfulness and tail biting, and to develop successful strategies and interventions to prevent and reduce tail biting.

Hypothalamic vasotocin and tyrosine hydroxylase levels following maternal care and selection for low mortality in laying hens

BACKGROUND

Feather pecking and cannibalism are major concerns in poultry farming, both in terms of animal welfare and farm economics. Genetic selection and introduction of (aspects of) maternal care have been suggested as potential interventions to reduce feather pecking in laying hens. Altered brain development has been proposed to reflect welfare states in animals, and can provide more insight into the underlying processes involved in feather pecking. Both vasotocin (the avian homologue of vasopressin) and dopaminergic neural circuitry have roles in control of social behaviors as well as in the stress response, and may be linked to feather pecking. Thus, the hypothalamus of adult laying hens selected for low early mortality (LML), which show low feather pecking, was examined and compared with a control line of adult laying hens selected for production characteristics only (CL). The effect of foster hen rearing on the two genetic lines and their hypothalamic morphology was also investigated.

RESULTS

We demonstrated an increase in the number of neurons positive for the rate-limiting enzyme in dopamine production, tyrosine hydroxylase, in the periventricular area of the hypothalamus in the LML hens compared to CL hens. Hen-reared chicks showed more vasotocin -positive neurons in the medial pre-optic area compared to the hens raised without a hen. No correlations were found between behavior in an open field at 5-6 weeks of age, and the histology of the same hens at adulthood.

CONCLUSION

The hypothalamic dopaminergic and vasotinergic systems are altered in hens following genetic selection or maternal care, indicating a potential role for these systems in feather pecking.

Modelling of feather pecking behavior in beak-trimmed and non-beak-trimmed crossbred laying hens: variance component and trait-based approach

Because of a ban on the use of beak trimming in some European countries, feather pecking is becoming a substantial problem in the layer industry, both from animal welfare and economic points of view. The feather condition score (FCS) as a measure of feather damage has been shown to be closely related to feather pecking behavior in laying hens housed in groups. To obtain a better understanding of genetic and other biological mechanisms underlying feather pecking behavior, data on FCS of a population of 2,724 female offspring from crossing 50 male W1 and 907 female WB purebred lines were used. The offspring of 25 sires were beak-trimmed, and the offspring of another 25 sires were non-beak-trimmed. Titers of plasma natural antibody (NAb) isotypes IgM and IgG binding keyhole limpet hemocyanin at 24 wk of age were measured. Feather condition was scored at 53 wk of age. In the first part of the present study, we estimated genetic parameters for FCS with 2 variance components models: a traditional linear animal model and a model combining direct and associative genetic effects. In the second part of the present study, a trait-based analysis for FCS was conducted to investigate whether NAb isotype titers can explain variation in FCS among individuals, by fitting a linear mixed model. Though the estimated associative genetic variance was substantial, associative effects for FCS were not statistically significant in both populations (P = 0.09 in beak-trimmed birds, and P = 0.08 in non-beak-trimmed birds). This suggests an insufficient number of records on FCS. Individual's NAb isotypes titers did not show direct effect for FCS of itself, but individual's IgG titers showed a suggestive effect on the FCS of cage mates (associative effect) in beak-trimmed laying hens, which need further confirmation.

Serotonin release in the caudal nidopallium of adult laying hens genetically selected for high and low feather pecking behavior: an in vivo microdialysis study

Severe feather pecking (FP) is a detrimental behavior causing welfare problems in laying hens. Divergent genetic selection for FP in White Leghorns resulted in strong differences in FP incidences between lines. More recently, it was shown that the high FP (HFP) birds have increased locomotor activity as compared to hens of the low FP (LFP) line, but whether these lines differ in central serotonin (5-hydroxytryptamine, 5-HT) release is unknown. We compared baseline release levels of central 5-HT, and the metabolite 5-HIAA in the limbic and prefrontal subcomponents of the caudal nidopallium by in vivo microdialysis in adult HFP and LFP laying hens from the ninth generation of selection. A single subcutaneous d-fenfluramine injection (0.5 mg/kg) was given to release neuronal serotonin in order to investigate presynaptic storage capacity. The present study shows that HFP hens had higher baseline levels of 5-HT in the caudal nidopallium as compared to LFP laying hens. Remarkably, no differences in plasma tryptophan levels (precursor of 5-HT) between the lines were observed. d-fenfluramine increased 5-HT levels in both lines similarly indirectly suggesting that presynaptic storage capacity was the same. The present study shows that HFP hens release more 5-HT under baseline conditions in the caudal nidopallium as compared to the LFP birds. This suggests that HFP hens are characterized by a higher tonic 5-HT release.

Effects of feather pecking phenotype (severe feather peckers, victims and non-peckers) on serotonergic and dopaminergic activity in four brain areas of laying hens (Gallus gallus domesticus)

Severe feather pecking (SFP) in laying hens is a detrimental behavior causing loss of feathers, skin damage and cannibalism. Previously, we have associated changes in frontal brain serotonin (5-HT) turnover and dopamine (DA) turnover with alterations in feather pecking behavior in young pullets (28-60 days). Here, brain monoamine levels were measured in adult laying hens; focusing on four brain areas that are involved in emotional behavior or are part of the basal ganglia-thalamopallial circuit, which is involved in obsessive compulsive disorders. Three behavioral phenotypes were studied: Severe Feather Peckers (SFPs), Victims of SFP, and Non-Peckers (NPs). Hens (33 weeks old) were sacrificed after a 5-min manual restraint test. SFPs had higher 5-HIAA levels and a higher serotonin turnover (5-HIAA/5-HT) in the dorsal thalamus than NPs, with intermediate levels in victims. NPs had higher 5-HT levels in the medial striatum than victims, with levels of SFPs in between. 5-HT turnover levels did not differ between phenotypes in medial striatum, arcopallium and hippocampus. DA turnover levels were not affected by feather pecking phenotype. These findings indicate that serotonergic neurotransmission in the dorsal thalamus and striatum of adult laying hens depends on differences in behavioral feather pecking phenotype, with, compared to non-pecking hens, changes in both SFP and their victims. Further identification of different SFP phenotypes is needed to elucidate the role of brain monoamines in SFP.

Behavioural and Brain Gene Expression Profiling in Pigs during Tail Biting Outbreaks - Evidence of a Tail Biting Resistant Phenotype

Abnormal tail biting behaviour is a major welfare problem for pigs receiving the behaviour, as well as an indication of decreased welfare in the pigs performing it. However, not all pigs in a pen perform or receive tail biting behaviour and it has recently been shown that these 'neutral' pigs not only differ in their behaviour, but also in their gene expression compared to performers and receivers of tail biting in the same pen. To investigate whether this difference was linked to the cause or a consequence of them not being involved in the outbreak of tail biting, behaviour and brain gene expression was compared with 'control' pigs housed in pens with no tail biting. It was shown that the pigs housed in control pens performed a wider variety of pig-directed abnormal behaviour (belly nosing 0.95±1.59, tail in mouth 0.31±0.60 and 'other' abnormal 1.53±4.26; mean±S.D) compared to the neutral pigs (belly nosing 0.30±0.62, tail in mouth 0.13±0.50 and "other" abnormal 0.42±1.06). With Affymetrix gene expression arrays, 107 transcripts were identified as differently expressed (p<0.05) between these two categories of pigs. Several of these transcripts had already been shown to be differently expressed in the neutral pigs when they were compared to performers and receivers of tail biting in the same pen in an earlier study. Hence, the different expression of these genes cannot be a consequence of the neutral pigs not being involved in tail biting behaviour, but rather linked to the cause contributing to why they were not involved in tail biting interactions. These neutral pigs seem to have a genetic and behavioural profile that somehow contributes to them being resistant to performing or receiving pig-directed abnormal behaviour, such as tail biting, even when housed in an environment that elicits that behaviour in other pigs.

Brain gene expression differences are associated with abnormal tail biting behavior in pigs

Knowledge about gene expression in animals involved in abnormal behaviors can contribute to the understanding of underlying biological mechanisms. This study aimed to explore the motivational background to tail biting, an abnormal injurious behavior and severe welfare problem in pig production. Affymetrix microarrays were used to investigate gene expression differences in the hypothalamus and prefrontal cortex of pigs performing tail biting, pigs receiving bites to the tail and neutral pigs who were not involved in the behavior. In the hypothalamus, 32 transcripts were differentially expressed (P < 0.05) when tail biters were compared with neutral pigs, 130 when comparing receiver pigs with neutrals, and two when tail biters were compared with receivers. In the prefrontal cortex, seven transcripts were differently expressed in tail biters when compared with neutrals, seven in receivers vs. neutrals and none in the tail biters vs. receivers. In total, 19 genes showed a different expression pattern in neutral pigs when compared with both performers and receivers. This implies that the functions of these may provide knowledge about why the neutral pigs are not involved in tail biting behavior as performers or receivers. Among these 19 transcripts were genes associated with production traits in pigs (PDK4), sociality in humans and mice (GTF2I) and novelty seeking in humans (EGF). These are in line with hypotheses linking tail biting with reduced back fat thickness and explorative behavior.

Differential gene expression from genome-wide microarray analyses distinguishes Lohmann Selected Leghorn and Lohmann Brown layers

The Lohmann Selected Leghorn (LSL) and Lohmann Brown (LB) layer lines have been selected for high egg production since more than 50 years and belong to the worldwide leading commercial layer lines. The objectives of the present study were to characterize the molecular processes that are different among these two layer lines using whole genome RNA expression profiles. The hens were kept in the newly developed small group housing system Eurovent German with two different group sizes. Differential expression was observed for 6,276 microarray probes (FDR adjusted P-value <0.05) among the two layer lines LSL and LB. A 2-fold or greater change in gene expression was identified on 151 probe sets. In LSL, 72 of the 151 probe sets were up- and 79 of them were down-regulated. Gene ontology (GO) enrichment analysis accounting for biological processes evinced 18 GO-terms for the 72 probe sets with higher expression in LSL, especially those taking part in immune system processes and membrane organization. A total of 32 enriched GO-terms were determined among the 79 down-regulated probe sets of LSL. Particularly, these terms included phosphorus metabolic processes and signaling pathways. In conclusion, the phenotypic differences among the two layer lines LSL and LB are clearly reflected in their gene expression profiles of the cerebrum. These novel findings provide clues for genes involved in economically important line characteristics of commercial laying hens.

Identification of chromosomal locations associated with tail biting and being a victim of tail-biting behaviour in the domestic pig (Sus scrofa domesticus)

The objective of this study was to identify loci associated with tail biting or being a victim of tail biting in Norwegian crossbred pigs using a genome-wide association study with PLINK case-control analysis. DNA was extracted from hair or blood samples collected from 98 trios of crossbred pigs located across Norway. Each trio came from the same pen and consisted of one pig observed to initiate tail biting, one pig which was the victim of tail biting and a control pig which was not involved in either behaviour. DNA was genotyped using the Illumina PorcineSNP60 BeadChip whole-genome single-nucleotide polymorphism (SNP) assay. After quality assurance filtering, 53,952 SNPs remained comprising 74 animals (37 pairs) for the tail biter versus control comparison and 53,419 SNPs remained comprising 80 animals (40 pairs) for the victim of tail biting versus control comparison. An association with being a tail biter was observed on Sus scrofa chromosome 16 (SSC16; p = 1.6 × 10(-5)) and an unassigned chromosome (p = 3.9 × 10(-5)). An association with being the victim of tail biting was observed on Sus scrofa chromosomes 1 (SSC1; p = 4.7 × 10(-5)), 9 (SSC9; p = 3.9 × 10(-5)), 18 (SSC18; p = 7 × 10(-5) for 9,602,511 bp, p = 3.4 × 10(-5) for 9,653,881 bp and p = 5.3 × 10(-5) for 29,577,783 bp) and an unassigned chromosome (p = 6.1 × 10(-5)). An r(2) = 0.96 and a D' = 1 between the two SNPs at 9 Mb on SSC18 indicated extremely high linkage disequilibrium, suggesting that these two markers represent a single locus. These results provide evidence of a moderate genetic association between the propensity to participate in tail-biting behaviour and the likelihood of becoming a victim of this behaviour.