Differences in intestinal microbial metabolites in laying hens with high and low levels of repetitive feather-pecking behavior

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.

Cecal microbiota transplantation: unique influence of cecal microbiota from divergently selected inbred donor lines on cecal microbial profile, serotonergic activity, and aggressive behavior of recipient chickens

BACKGROUND

Accumulating evidence from human trials and rodent studies has indicated that modulation of gut microbiota affects host physiological homeostasis and behavioral characteristics. Similarly, alterations in gut microbiota could be a feasible strategy for reducing aggressive behavior and improving health in chickens. The study was conducted to determine the effects of early-life cecal microbiota transplantation (CMT) on cecal microbial composition, brain serotonergic activity, and aggressive behavior of recipient chickens.

METHODS

Chicken lines 6₃ and 7₂ with nonaggressive and aggressive behavior, respectively, were used as donors and a commercial strain Dekalb XL was used as recipients for CMT. Eighty-four 1-d-old male chicks were randomly assigned to 1 of 3 treatments with 7 cages per treatment and 4 chickens per cage (n = 7): saline (control, CTRL), cecal solution of line 6₃ (6₃-CMT), and cecal solution of line 7₂ (7₂-CMT). Transplantation was conducted via oral gavage once daily from d 1 to 10, and then boosted once weekly from week 3 to 5. At weeks 5 and 16, home-cage behavior was recorded, and chickens with similar body weights were assigned to paired aggression tests between the treatments. Samples of blood, brain, and cecal content were collected from the post-tested chickens to detect CMT-induced biological and microbiota changes.

RESULTS

6₃-CMT chickens displayed less aggressive behavior with a higher hypothalamic serotonergic activity at week 5. Correspondingly, two amplicon sequence variants (ASVs) belonging to Lachnospiraceae and one Ruminococcaceae UCG-005 ASV were positively correlated with the levels of brain tryptophan and serotonin, respectively. 7₂-CMT chickens had lower levels of brain norepinephrine and dopamine at week 5 with higher levels of plasma serotonin and tryptophan at week 16. ASVs belonging to Mollicutes RF39 and GCA-900066225 in 7₂-CMT chickens were negatively correlated with the brain 5-hydroxyindoleacetic acid (5-HIAA) at week 5, and one Bacteroides ASV was negatively correlated with plasma serotonin at week 16.

CONCLUSION

Results indicate that CMT at an early age could regulate aggressive behavior via modulating the cecal microbial composition, together with central serotonergic and catecholaminergic systems in recipient chickens. The selected CMT could be a novel strategy for reducing aggressive behavior through regulating signaling along the microbiota-gut-brain axis.

Restorative effects of Lactobacillus rhamnosus LR-32 on the gut microbiota, barrier integrity, and 5-HT metabolism in reducing feather-pecking behavior in laying hens with antibiotic-induced dysbiosis

The development of abnormal feather-pecking (FP) behavior, where laying hens display harmful pecks in conspecifics, is multifactorial and has been linked to the microbiota-gut-brain axis. Antibiotics affect the gut microbial composition, leading to gut-brain axis imbalance and behavior and physiology changes in many species. However, it is not clear whether intestinal dysbacteriosis can induce the development of damaging behavior, such as FP. The restorative effects of Lactobacillus rhamnosus LR-32 against intestinal dysbacteriosis-induced alternations need to be determined either. The current investigation aimed to induce intestinal dysbacteriosis in laying hens by supplementing their diet with the antibiotic lincomycin hydrochloride. The study revealed that antibiotic exposure resulted in decreased egg production performance and an increased tendency toward severe feather-pecking (SFP) behavior in laying hens. Moreover, intestinal and blood-brain barrier functions were impaired, and 5-HT metabolism was inhibited. However, treatment with Lactobacillus rhamnosus LR-32 following antibiotic exposure significantly alleviated the decline in egg production performance and reduced SFP behavior. Lactobacillus rhamnosus LR-32 supplementation restored the profile of the gut microbial community, and showed a strong positive effect by increasing the expression of tight junction proteins in the ileum and hypothalamus and promoting the expression of genes related to central 5-HT metabolism. The correlation analysis revealed that probiotic-enhanced bacteria were positively correlated, and probiotic-reduced bacteria were negatively correlated with tight junction-related gene expression, and 5-HT metabolism, and butyric acid levels. Overall, our findings indicate that dietary supplementation with Lactobacillus rhamnosus LR-32 can reduce antibiotic-induced FP in laying hens and is a promising treatment to improve the welfare of domestic birds.

Disturbed circadian rhythm of locomotor activity of pullets is related to feather pecking in laying hens

Various aspects of activity, such as spontaneous activity, explorative activity, activity in open-field tests, and hyperactivity syndrome have been explored as causal factors of feather pecking in laying hens, with no clear results. In all previous studies, mean values of activity over different time intervals were used as criteria. Incidental observation of alternated oviposition time in lines selected for high (HFP) and low feather pecking (LFP), supported by a recent study which showed differentially expressed genes related to the circadian clock in the same lines, led to the hypothesis that feather pecking may be related to a disturbed diurnal activity rhythm. Hence activity recordings of a previous generation of these lines have been reanalyzed. Data sets of a total of 682 pullets of 3 subsequent hatches of HFP, LFP, and an unselected control line (CONTR) were used. Locomotor activity was recorded in pullets housed in groups of mixed lines in a deep litter pen on 7 consecutive 13-h light phases, using a radio-frequency identification antenna system. The number of approaches to the antenna system was recorded as a measure of locomotor activity and analyzed using a generalized linear mixed model including hatch, line, time of day and the interactions of hatch × time of day and line × time of day as fixed effects. Significant effects were found for time and the interaction line × time of day but not for line. All lines showed a bimodal pattern of diurnal activity. The peak activity of the HFP in the morning was lower than that of the LFP and CONTR. In the afternoon peak all lines differed with the highest mean in the LFP followed by CONTR and HFP. The present results provide support for the hypothesis that a disturbed circadian clock plays a role in the development of feather pecking.

Connecting gut microbiomes and short chain fatty acids with the serotonergic system and behavior in Gallus gallus and other avian species

The chicken gastrointestinal tract has a diverse microbial community. There is increasing evidence for how this gut microbiome affects specific molecular pathways and the overall physiology, nervous system and behavior of the chicken host organism due to a growing number of studies investigating conditions such as host diet, antibiotics, probiotics, and germ-free and germ-reduced models. Systems-level investigations have revealed a network of microbiome-related interactions between the gut and state of health and behavior in chickens and other animals. While some microbial symbionts are crucial for maintaining stability and normal host physiology, there can also be dysbiosis, disruptions to nutrient flow, and other outcomes of dysregulation and disease. Likewise, alteration of the gut microbiome is found for chickens exhibiting differences in feather pecking (FP) behavior and this alteration is suspected to be responsible for behavioral change. In chickens and other organisms, serotonin is a chief neuromodulator that links gut microbes to the host brain as microbes modulate the serotonin secreted by the host's own intestinal enterochromaffin cells which can stimulate the central nervous system via the vagus nerve. A substantial part of the serotonergic network is conserved across birds and mammals. Broader investigations of multiple species and subsequent cross-comparisons may help to explore general functionality of this ancient system and its increasingly apparent central role in the gut-brain axis of vertebrates. Dysfunctional behavioral phenotypes from the serotonergic system moreover occur in both birds and mammals with, for example, FP in chickens and depression in humans. Recent studies of the intestine as a major site of serotonin synthesis have been identifying routes by which gut microbial metabolites regulate the chicken serotonergic system. This review in particular highlights the influence of gut microbial metabolite short chain fatty acids (SCFAs) on the serotonergic system. The role of SCFAs in physiological and brain disorders may be considerable because of their ability to cross intestinal as well as the blood-brain barriers, leading to influences on the serotonergic system via binding to receptors and epigenetic modulations. Examinations of these mechanisms may translate into a more general understanding of serotonergic system development within chickens and other avians.

Influence of different dietary fibre contents in the diet on feather pecking, locomotor activity and performance of laying hens

1. This trial investigated the effects of three diets with increasing proportions of insoluble dietary fibre (3%, 6% and 9%) but with similar metabolisable energy on behaviour, plumage condition and laying performance of Lohmann Tradition hens.2. At 21 weeks of age, four groups of 20 hens each (= four replicates/treatment) were randomly assigned to one of the three feeding treatments and exclusively fed with their assigned feed until the end of the laying period.3. Severe feather pecking decreased with increasing fibre content (3%: 0.78 pecks/30min/hen, 6%: 0.31, 9%: 0.12; P<0.0001). In contrast, no effect of fibre was seen for gentle feather pecking (P=0.19) and aggressive pecking (P=0.84). The number of free feathers in the littered area increased with increasing fibre content (3%: 0.06 feathers/625cm²/hen, 6%: 0.09, 9%: 0.16; P=0.0074). Over time plumage quality worsened in all hens, but was consistently better with increasing fibre content (fibre content x sampling period; P<0.0001). Locomotor activity was similar across all treatments, except for a slight decrease in hens fed the 3% fibre diet at the end of the experimental period. No effect of fibre content on hens' weight (P=0.75) was detectable. Similarly, performance did not differ between hens fed varying dietary fibre.4. The results supported the assumption that increasing dietary fibre helps to reduce the risk for the occurrence of feather pecking in laying hens, i.e., improve well-being, while having no negative effects on performance.

Regulatory T Cell Modulation by Lactobacillus rhamnosus Improves Feather Damage in Chickens

It is currently unclear whether potential probiotics such as lactic acid bacteria could affect behavioral problems in birds. To this end, we assessed whether a supplementation of Lactobacillus rhamnosus JB-1 can reduce stress-induced severe feather pecking (SFP), feather damage and fearfulness in adult birds kept for egg laying. In parallel, we assessed SFP genotypic and phenotypic-related immune responses and aromatic amino acid status linked to neurotransmitter production. Social stress aggravated plumage damage, while L. rhamnosus treatment improved the birds' feather cover in non-stressed birds, but did not impact fearfulness. Our data demonstrate the significant impact of L. rhamnosus supplementation on the immune system. L. rhamnosus supplementation induced immunosuppressive regulatory T cells and cytotoxic T cells in both the cecal tonsils and the spleen. Birds exhibiting the SFP phenotype possessed lower levels of cecal tonsils regulatory T cells, splenic T helper cells and a lower TRP:(PHE+TYR). Together, these results suggest that bacteria may have beneficial effects on the avian immune response and may be useful therapeutic adjuncts to counteract SFP and plumage damage, thus increasing animal health and welfare.

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 Impact of Probiotic Bacillus subtilis on Injurious Behavior in Laying Hens

Simple Summary

Injurious behavior prevention is a critical issue in the poultry industry due to increasing social stress, leading to negative effects on bird production and survivability, consequently enhancing gut microbiota dysbiosis and neuroinflammation via the microbiota–gut–brain axis. Probiotics have been used as potential therapeutic psychobiotics to treat or improve neuropsychiatric disorders or symptoms by boosting cognitive and behavioral processes and reducing stress reactions in humans and various experimental animals. The current data will first report that probiotic Bacillus subtilis reduces stress-induced injurious behavior in laying hens via regulating microbiota–gut–brain function with the potential to be an alternative to beak trimming during poultry egg production.

Abstract

Intestinal microbiota functions such as an endocrine organ to regulate host physiological homeostasis and behavioral exhibition in stress responses via regulating the gut–brain axis in humans and other mammals. In humans, stress-induced dysbiosis of the gut microbiota leads to intestinal permeability, subsequently affecting the clinical course of neuropsychiatric disorders, increasing the frequency of aggression and related violent behaviors. Probiotics, as direct-fed microorganism, have been used as dietary supplements or functional foods to target gut microbiota (microbiome) for the prevention or therapeutic treatment of mental diseases including social stress-induced psychiatric disorders such as depression, anxiety, impulsivity, and schizophrenia. Similar function of the probiotics may present in laying hens due to the intestinal microbiota having a similar function between avian and mammals. In laying hens, some management practices such as hens reared in conventional cages or at a high stocking density may cause stress, leading to injurious behaviors such as aggressive pecking, severe feather pecking, and cannibalism, which is a critical issue facing the poultry industry due to negative effects on hen health and welfare with devastating economic consequences. We discuss the current development of using probiotic Bacillus subtilis to prevent or reduce injurious behavior in laying hens.

Gut Microbiota Implications for Health and Welfare in Farm Animals: A Review

Simple Summary

Farm animal health and welfare have been paid increasing concern in the world, which is generally assessed by the measurements of physical health, immune response, behavior, and physiological indicators, such as stress-related hormone, cortisone, and norepinephrine. Gut microbiota as a “forgotten organ” has been reported for its great influence on the host phenotypes through the immune, neural, and endocrine pathways to affect the host health and behavior. In addition, fecal microbiota transplantation as a novel approach is applied to regulating the composition and function of the recipient farm animals. In this review, we summarized recent studies that gut microbiota influenced health, immunity, behavior, and stress response, as well as the progress of fecal microbiota transplantation in farm animals. The review will provide new insights into the measurement of farm animal health and welfare concerning gut microbiota, and the implication of fecal microbiota transplantation to improve productivity, health, and welfare. Above all, this review suggests that gut microbiota is a promising field to evaluate and improve animal welfare.

Abstract

In the past few decades, farm animal health and welfare have been paid increasing concern worldwide. Farm animal health and welfare are generally assessed by the measurements of physical health, immune response, behavior, and physiological indicators. The gut microbiota has been reported to have a great influence on host phenotypes, possibly via the immune processes, neural functions, and endocrine pathways, thereby influencing host phenotypes. However, there are few reviews regarding farm animals’ health and welfare status concerning the gut microbiota. In this point of view, (1) we reviewed recent studies showing that gut microbiota (higher alpha diversity, beneficial composition, and positive functions) effectively influenced health characteristics, immunity, behaviors, and stress response in farm animals (such as pigs, chickens, and cows), which would provide a novel approach to measure and evaluate the health status and welfare of farm animals. In addition, fecal microbiota transplantation (FMT) as one of the methods can modulate the recipient individual’s gut microbiota to realize the expected phenotype. Further, (2) we highlighted the application of FMT on the improvement of the production performance, the reduction in disease and abnormal behavior, as well as the attenuation of stress in farm animals. It is concluded that the gut microbiota can be scientifically used to assess and improve the welfare of farm animals. Moreover, FMT may be a helpful strategy to reduce abnormal behavior and improve stress adaption, as well as the treatment of disease for farm animals. This review suggests that gut microbiota is a promising field to evaluate and improve animal welfare.

The gut microbiota and microbial metabolites are associated with tail biting in pigs

Tail biting is an abnormal behaviour that causes stress, injury and pain. Given the critical role of the gut-microbiota in the development of behavioural problems in humans and animals, the aim of this study was to determine whether pigs that are biters, victims of tail biting or controls (nine matched sets of pigs) have a different microbiota composition, diversity and microbial metabolite profile. We collected faecal and blood samples from each individual for analysis. The gut microbiota composition was most different between the biter and the control pigs, with a higher relative abundance of Firmicutes in tail biter pigs than the controls. Furthermore, we detected differences in faecal and plasma short chain fatty acids (SCFA) profiles between the biter and victim pigs, suggesting physiological differences even though they are kept in the same pen. Thus, in addition to supporting an association between the gut microbiota and tail biting in pigs, this study also provides the first evidence of an association between tail biting and SCFA. Therefore, further research is needed to confirm these associations, to determine causality and to study how the SCFA profiles of an individual play a role in the development of tail biting behaviour.

Ingestion of Lactobacillus rhamnosus modulates chronic stress-induced feather pecking in chickens

Feather pecking (FP) is a stress-induced neuropsychological disorder of birds. Intestinal dysbiosis and inflammation are common traits of these disorders. FP is, therefore, proposed to be a behavioral consequence of dysregulated communication between the gut and the brain. Probiotic bacteria are known to favorably modulate the gut microbiome and hence the neurochemical and immune components of the gut-brain axis. Consequently, probiotic supplementation represents a promising new therapeutic to mitigate widespread FP in domestic chickens. We monitored FP, gut microbiota composition, immune markers, and amino acids related to the production of neurochemicals in chickens supplemented with Lactobacillus rhamnosus or a placebo. Data demonstrate that, when stressed, the incidence of FP increased significantly; however, L. rhamnosus prevented this increase. L. rhamnosus supplementation showed a strong immunological effect by increasing the regulatory T cell population of the spleen and the cecal tonsils, in addition to limiting cecal microbiota dysbiosis. Despite minimal changes in aromatic amino acid levels, data suggest that catecholaminergic circuits may be an interesting target for further studies. Overall, our findings provide the first data supporting the use of a single-strain probiotic to reduce stress-induced FP in chickens and promise to improve domestic birds' welfare.

Gut Microbial Composition and Predicted Functions Are Not Associated with Feather Pecking and Antagonistic Behavior in Laying Hens

BACKGROUND

Feather pecking is a well-known problem in layer flocks that causes animal welfare restrictions and contributes to economic losses. Birds' gut microbiota has been linked to feather pecking. This study aims to characterize the microbial communities of two laying hen lines divergently selected for high (HFP) and low (LFP) feather pecking and investigates if the microbiota is associated with feather pecking or agonistic behavior.

METHODS

Besides phenotyping for the behavioral traits, microbial communities from the digesta and mucosa of the ileum and caeca were investigated using target amplicon sequencing and functional predictions. Microbiability was estimated with a microbial mixed linear model.

RESULTS

Ileum digesta showed an increase in the abundance of the genus Lactobacillus in LFP, while Escherichia was abundant in HFP hens. In the caeca digesta and mucosa of the LFP line were more abundant Faecalibacterium and Blautia. Tryptophan metabolism and lysine degradation were higher in both digesta and mucosa of the HFP hens. Linear models revealed that the two lines differ significantly in all behavior traits. Microbiabilities were close to zero and not significant in both lines and for all traits.

CONCLUSIONS

Trait variation was not affected by the gut microbial composition in both selection lines.

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.

Advances in genetic selection and breeder practice improve commercial layer hen welfare

Modern commercial layer breeds represent the culmination of ~7000 years of natural genetic selection. This selection was driven in former times by a combination of genetic-shift and -drift events, that led to chickens being favoured as domesticated species for meat and egg production. More recently, in the early 20th century, the concept of hybrid vigour was discovered and accelerated the natural breeding progress that delivered new genetic lines and more favourable production traits. In the mid-20th century, the broiler-type and egg layer-type lines diverged and, in the 21st century, genetic analysis has further accelerated the progress made towards extended primary breeding characteristics such as egg quality, production and feed-intake traits, together with secondary breeding characteristics such as behavioural traits that have improved robustness in different housing systems, climates and feed types, which together have significantly improved welfare traits. Most recently, there has been the adoption of higher-powered computational analytics together with quantitative trait loci and single-nucleotide polymorphism assessment, which have further improved the uniformity of production traits within breeds. Most importantly, this has provided the primary breeding companies with improved and broader basis of selection of the modern commercial layer breeds, which also improved the alignment of layer strains with market requirements, and diverse variations in housing, nutritional and environmental conditions. This is also testament to the speed with which the commercial layer geneticists can respond to changing welfare policy on factors such as stocking density and beak treatment. The present paper reviews the modern approaches to genetic selection, including considerations of and benefits to the welfare state of commercial layers.

A Proposed Role for Pro-Inflammatory Cytokines in Damaging Behavior in Pigs

Sickness can change our mood for the worse, leaving us sad, lethargic, grumpy and less socially inclined. This mood change is part of a set of behavioral symptoms called sickness behavior and has features in common with core symptoms of depression. Therefore, the physiological changes induced by immune activation, for example following infection, are in the spotlight for explaining mechanisms behind mental health challenges such as depression. While humans may take a day off and isolate themselves until they feel better, farm animals housed in groups have only limited possibilities for social withdrawal. We suggest that immune activation could be a major factor influencing social interactions in pigs, with outbreaks of damaging behavior such as tail biting as a possible result. The hypothesis presented here is that the effects of several known risk factors for tail biting are mediated by pro-inflammatory cytokines, proteins produced by the immune system, and their effect on neurotransmitter systems. We describe the background for and implications of this hypothesis.

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.

Cecal motility and the impact of Lactobacillus in feather pecking laying hens

The gut-microbiota-brain axis is implicated in the development of behavioural disorders in mammals. As such, its potential role in disruptive feather pecking (FP) in birds cannot be ignored. Birds with a higher propensity to perform FP have distinct microbiota profiles and feed transit times compared to non-pecking counterparts. Consequently, we hypothesize that the gut microbiota is intimately linked to FP and gut motility, which presents the possibility of using probiotics to control FP behaviour. In the present study, we aim to assess the relationship between cecal motility and the probiotic Lactobacillus rhamnosus in chickens classified as peckers (P, 13 birds) and non-peckers (NP, 17 birds). We show that cecal contractions were 68% less frequent and their amplitude increased by 58% in the presence of L. rhamnosus. Furthermore, the number of FP bouts performed by P birds was positively correlated with contraction velocity and amplitude. We present the first account of gut motility measurements in birds with distinct FP phenotypes. Importantly, the present work demonstrates the clear impact of a probiotic on cecal contractions. These findings lay the foundation for identifying biological differences between P and NP birds which will support the development of FP control strategies.

Differences in gut microbiota composition of laying hen lines divergently selected on feather pecking

Feather pecking (FP), a damaging behavior where laying hens peck and pull at feathers of conspecifics, is multifactorial and has been linked to numerous behavioral and physiological characteristics. The gut microbiota has been shown to influence host behavior and physiology in many species, and could therefore affect the development of damaging behaviors, such as FP. Yet, it is unknown whether FP genotypes (high FP [HFP] and low FP [LFP] lines) or FP phenotypes (i.e., individuals differing in FP, feather peckers and neutrals) differ in their gut microbiota composition. Therefore, we identified mucosa-associated microbiota composition of the ileum and cecum at 10 and 30 wk of age. At 30 wk of age, we further identified luminal microbiota composition from combined content of the ileum, ceca, and colon. FP phenotypes could not be distinguished from each other in mucosa-associated or luminal microbiota composition. However, HFP neutrals were characterized by a higher relative abundance of genera of Clostridiales, but lower relative abundance of Lactobacillus for the luminal microbiota composition compared to LFP phenotypes. Furthermore, HFP neutrals had a higher diversity and evenness for the luminal microbiota compared to LFP phenotypes. FP genotypes could not be distinguished from each other in mucosa-associated microbiota composition. Yet, FP genotypes could be distinguished from each other in luminal microbiota composition. HFP birds were characterized by a higher relative abundance of genera of Clostridiales, but lower relative abundance of Staphylococcus and Lactobacillus compared to LFP birds. Furthermore, HFP birds had a higher diversity and evenness for both cecal mucosa-associated and luminal microbiota compared to LFP birds at adult age. In conclusion, we here show that divergent selection on FP can (in)directly affect luminal microbiota composition. Whether differences in microbiota composition are causal to FP or a consequence of FP remains to be elucidated.

Chickens selected for feather pecking can inhibit prepotent motor responses in a Go/No-Go task

Repetitive feather pecking (FP) where birds peck and pull out feathers of conspecifics could reflect motor impulsivity through a lack of behavioural inhibition. We assessed motor impulsivity in female chickens (n = 20) during a Go/No-Go task where birds had to peck (Go) or inhibit pecks (No-Go) appropriately to obtain a food reward, depending on visual cues in an operant chamber. Birds were selected to show divergent FP performance based on their genotype (high predisposition for FP or unselected control line) and phenotype (peckers or non-peckers). Genotype, phenotype, and its interaction did not affect the number of pre-cue responses, percentage of responses during No-Go cues (false alarms), or efficiency (number of rewards over number of responses). We present the first documentation of a Go/No-Go task to measure the ability of birds genetically and phenotypically selected for FP activity to inhibit a prepotent motor response. Results indicate that the repetitive motor action of FP does not reflect impulsivity and is not genetically linked to a lack of behavioural inhibition as measured in a Go/No-Go task.

Early-life microbiota transplantation affects behavioural responses, serotonin and immune characteristics in chicken lines divergently selected on feather pecking

Gut microbiota influences host behaviour and physiology, such as anxiety, stress, serotonergic and immune systems. These behavioural and physiological characteristics are related to feather pecking (FP), a damaging behaviour in chickens that reduces animal welfare and productivity. Moreover, high FP (HFP) and low FP (LFP) lines differed in microbiota composition. However, it is unknown whether microbiota can influence the development of FP. For the first time, we identified the effects of microbiota transplantation on FP, and behavioural and physiological characteristics related to FP. HFP and LFP chicks received sterile saline (control), HFP or LFP microbiota transplantation during the first two weeks post-hatch. Microbiota transplantation influenced behavioural responses of the HFP line during treatment and of the LFP line after treatment. In both lines, homologous microbiota transplantation (i.e., receiving microbiota from their line) resulted in more active behavioural responses. Furthermore, microbiota transplantation influenced immune characteristics (natural antibodies) in both lines and peripheral serotonin in the LFP line. However, limited effects on microbiota composition, stress response (corticosterone) and FP were noted. Thus, early-life microbiota transplantation had immediate and long-term effects on behavioural responses and long-term effects on immune characteristics and peripheral serotonin; however, the effects were dependent on host genotype. Since early-life microbiota transplantation influenced behavioural and physiological characteristics that are related to FP, it could thus influence the development of FP later in life.

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.

Assessing the effect of rate and extent of starch digestion on laying hen performance

The inclusion of starch with a lower rate and extent of digestion has proven to be beneficial in broiler production. However, less is known about its effect on laying hen performance. Therefore, 6 diets were formulated to produce differing ratios (0:100, 20:80, 40:60, 60:40, 80:20, and 100:0) of semi-purified wheat starch (rapidly digested) and pea starch (PS; slowly digested). Each diet was fed to 120 conventionally caged Lohmann LSL lite hens in groups of 12, from 27 to 46 wk of age, and its effects on performance and feather covering were assessed. Data were analyzed by regression analysis, and the significance level was chosen at P ≤ 0.05. Hen-day egg production (HDP) was high (97.05%) and unaffected by PS concentration for 0 to 10 wk of the trial, followed by a quadratic-shaped HDP, with an estimated maximum at 67% PS concentration, for the 10 to 20 wk period of the trial. Overall (0 to 20 wk), HDP increased linearly with PS. No effect on egg weight was found (average weight = 59.6±2.1 g), but eggshells were thickest at the 55% PS concentration. Body weight gain was affected by PS concentration and maximized at 49% PS. Body weight uniformity and mortality were not affected by dietary treatment. Feed intake increased linearly with PS from 102 to 109 g/hen/d, while feed: egg mass ratio was minimal at 26% PS. Using a scale from 1 to 4 per body part (neck, wings, back, vent and breast), only neck feather cover increased linearly with PS, from 3.0 (0% PS) to 3.2/4 (100% PS). However, back and total feather coverage showed a trend (P = 0.054 and P = 0.079 respectively) to increase linearly with PS as well (from 3.7 to 3.9/4 and 15.6 to 16.6/20, respectively). In summary, feeding PS at low to intermediate concentrations improved laying hen performance. Further research should focus on the mechanisms involved in this effect.

Differences in cecal microbiome of selected high and low feather-pecking laying hens

In mammals, it has become increasingly clear that the gut microbiota influences not only gastrointestinal physiology but also modulates behavior. In domestic birds, ceca have the greatest gastrointestinal microbial population. Feather-pecking (FP) behavior in laying hens is one of the most important unsolved behavioral issues in modern agriculture. The aim of the present study was to assess the cecal microbial community of divergently selected high (HFP; n = 20) and low (LFP; n = 20) feather-pecking birds at 60 wk of age. The cecal samples were subjected to community profiling of 16S rRNA and in silico metagenomics using a modified bar-coded Illumina sequencing method on a MiSeq Illumina sequencer. Our results revealed that compared to HFP birds, LFP birds are characterized by an increased overall microbial diversity (beta diversity) shown by a difference in the Bray–Curtis index (R² = 0.171, P < 0.05). Furthermore, operational taxonomic unit comparisons showed an increased presence of Clostridiae and decreased presence of Lactobaccillacae in HFP birds when compared to LFP birds (False Discovery Rate < 0.05, Mann–Whitney comparisons). Our data indicate that there may be differences in the cecal profile between these 2 lines of laying hens. More research, building on this first study using sequencing technology for profiling the chicken cecal microbiome, will be needed in order to reveal if and how there exists a functional link between the performance of FP and the cecal microbial community.

Insect-based diet, a promising nutritional source, modulates gut microbiota composition and SCFAs production in laying hens

Insects could be potential nutritional sources both for humans and animals. Among these, Hermetia illucens, with good amount of chitin and proteins, represents a suitable diet replacement for laying hens. Little is known about insect diet effects on the microbial ecology of the gastrointestinal tract and bacterial metabolites production. In this study we investigated the effect of H. illucens larvae meal administration on cecal microbiota and short chain fatty acids (SCFAs) production in laying hens. 16S rDNA sequencing showed strong differences between cecal microbiota of soybean (SD) and insect diet (ID) groups both in type and relative abundance (unweighted and weighted beta diversity) of microbial species. In particular, Bacteroides plebeius, Elusimicrobium minutum, Alkaliphilus transvaalensis, Christensenella minuta, Vallitalea guaymasensis and Flavonifractor plautii represented the principal contributors of changes in gut microbiota composition of ID group (FDR p-values < 0.05). Of these, F. plautii, C. minuta and A. transvaalensis have the potential to degrade the chitin’s insect meal and correlated with the observed high levels of gut SCFAs produced in ID group. These microorganisms may thus connect the chitin degradation with high SCFAs production. Our results suggest H. illucens as a potential prebiotic by well feeding gut microbiota.

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.

Quantitative genetic analysis of causal relationships among feather pecking, feather eating, and general locomotor activity in laying hens using structural equation models

The objective of this research was to analyze the relationship between feather pecking (FP) and feather eating (FE) as well as general locomotor activity (GLA) using structural equation models, which allow that one trait can be treated as an explanatory variable of another trait. This provides an opportunity to infer putative causal links among the traits. For the analysis, 897 F2-hens set up from 2 lines divergently selected for high and low FP were available. The FP observations were Box-Cox transformed, and FE and GLA observations were log and square root transformed, respectively. The estimated heritabilities of FE, GLA, and FP were 0.36, 0.29, and 0.20, respectively. The genetic correlation between FP and FE (GLA) was 0.17 (0.04). A high genetic correlation of 0.47 was estimated between FE and GLA. The recursive effect from FE to FP was [Formula: see text], and from GLA to FP [Formula: see text] These results imply that an increase of FE leads to an increased FP behavior and that an increase in GLA results in a higher FP value. Furthermore, the study showed that the genetic correlation among the traits is mainly caused by indirect effects.

New biomarkers for intestinal permeability induced by lipopolysaccharide in chickens

Intestinal health is influenced by a complex set of variables involving the intestinal microbiota, mucosal immunity, digestion and absorption of nutrients, intestinal permeability (IP) and intestinal integrity. An increase in IP increases bacterial or toxin translocation, activates the immune system and affects health. IP in chickens is reviewed in three sections. First, intestinal structure and permeability are discussed briefly. Second, the use of lipopolysaccharide (LPS) as a tool to increase IP is discussed in detail. LPS, a glycolipid found in the outer coat of mostly Gram-negative bacteria, has been reported to increase IP in rats, mice and pigs. Although LPS has been used in chickens for inducing systemic inflammation, information regarding LPS effects on IP is limited. This review proposes that LPS could be used as a means to increase IP in chickens. The final section focuses on potential biomarkers to measure IP, proposing that the sugar-recovery method may be optimal for application in chickens.

Diet structure, butyric acid, and fermentable carbohydrates influence growth performance, gut morphology, and cecal fermentation characteristics in broilers

An experiment with 288 male (Ross 308) 1-d-old broilers was conducted to test the hypothesis that a coarse diet supplemented with butyric acid (BA) and fermentable carbohydrates (FC) improves performance of broilers with a poorly digestible protein source. The interaction effects of diet structure (fine or coarse), FC supplementation (with or without), and BA supplementation (with or without) in a poorly digestible diet based on rapeseed meal (RSM) were tested in a factorial arrangement of 8 (2×2×2) dietary treatments. The coarseness of the diet affected feed intake (FI) (P<0.001), BW gain (P=0.001), and the feed conversion ratio (FCR) (P=0.001) positively. Broilers fed the coarse diets had, on average, 14% heavier gizzards and 11, 7, 5, and 6% lower relative empty weights of the crop, duodenum, jejunum, and ileum, respectively, compared with those fed the fine diets. Dietary coarseness resulted in, on average, 6% greater ileal protein digestibility, 20% lower gizzard pH, 19% greater villus height, 18% lower crypt depth, and 23% reduced cecal branched chain fatty acids (BCFA) compared with chickens fed the fine diets. Broilers fed BA-supplemented diets had an improved FCR (P=0.004) and decreased crypt depth (P<0.001) compared with those fed diets without BA. Fermentable carbohydrate supplementation did not influence growth performance, gut development, or contents of total BCFA and total biogenic amines in the cecal digesta (P>0.05). Supplementation with FC, however, decreased the cecal concentration of spermine by approximately 31% compared with broilers fed diets without FC (P=0.002). In conclusion, feeding a coarse diet supplemented with BA improved performance of broilers fed a diet containing a poorly digestible protein source. The negative effects of a poorly digestible protein source can thus be partly counterbalanced by coarse grinding and BA supplementation in the diet.

Genetic parameters for feather pecking and aggressive behavior in a large F2-cross of laying hens using generalized linear mixed models

Feather pecking and aggressive pecking is a well-known problem in egg production. In the present study, genetic parameters for 4 feather-pecking-related traits were estimated using generalized linear mixed models. The traits were bouts of feather pecking delivered (FPD), bouts of feather pecking received (FPR), bouts of aggressive pecking delivered (APD), and bouts of aggressive pecking received (APR). An F2-design was established from 2 divergent selected founder lines. The lines were selected for low or high feather pecking for 10 generations. The number of F2 hens was 910. They were housed in pens with around 40 birds. Each pen was observed in 21 sessions of 20 min, distributed over 3 consecutive days. An animal model was applied that treated the bouts observed within 20 min as repeated observations. An over-dispersed Poisson distribution was assumed for observed counts and the link function was a log link. The model included a random animal effect, a random permanent environment effect, and a random day-by-hen effect. Residual variance was approximated on the link scale by the delta method. The results showed a heritability around 0.10 on the link scale for FPD and APD and of 0.04 for APR. The heritability of FPR was zero. For all behavior traits, substantial permanent environmental effects were observed. The approximate genetic correlation between FPD and APD (FPD and APR) was 0.81 (0.54). Egg production and feather eating records were collected on the same hens as well and were analyzed with a generalized linear mixed model, assuming a binomial distribution and using a probit link function. The heritability on the link scale for egg production was 0.40 and for feather eating 0.57. The approximate genetic correlation between FPD and egg production was 0.50 and between FPD and feather eating 0.73. Selection might help to reduce feather pecking, but this might result in an unfavorable correlated selection response reducing egg production. Feather eating and feather pecking are genetically correlated and this needs further investigation.

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.

Parents and early life environment affect behavioral development of laying hen chickens

Severe feather pecking (SFP) in commercial laying hens is a maladaptive behavior which is associated with anxiety traits. Many experimental studies have shown that stress in the parents can affect anxiety in the offspring, but until now these effects have been neglected in addressing the problem of SFP in commercially kept laying hens. We therefore studied whether parental stock (PS) affected the development of SFP and anxiety in their offspring. We used flocks from a brown and white genetic hybrid because genetic background can affect SFP and anxiety. As SFP can also be influenced by housing conditions on the rearing farm, we included effects of housing system and litter availability in the analysis. Forty-seven rearing flocks, originating from ten PS flocks were followed. Behavioral and physiological parameters related to anxiety and SFP were studied in the PS at 40 weeks of age and in the rearing flocks at one, five, ten and fifteen weeks of age. We found that PS had an effect on SFP at one week of age and on anxiety at one and five weeks of age. In the white hybrid, but not in the brown hybrid, high levels of maternal corticosterone, maternal feather damage and maternal whole-blood serotonin levels showed positive relations with offsprings' SFP at one week and offsprings' anxiety at one and five weeks of age. Disruption and limitation of litter supply at an early age on the rearing farms increased SFP, feather damage and fearfulness. These effects were most prominent in the brown hybrid. It appeared that hens from a brown hybrid are more affected by environmental conditions, while hens from a white hybrid were more strongly affected by parental effects. These results are important for designing measures to prevent the development of SFP, which may require a different approach in brown and white flocks.