DOES PREENING BEHAVIOR REDUCE THE PREVALENCE OF AVIAN FEATHER LICE (PHTHIRAPTERA: ISCHNOCERA)?

Animals defend themselves against parasites in many ways. Defenses, such as physiological immune responses, are capable of clearing some infections. External parasites that do not feed on blood, however, are not controlled by the physiological immune system. Instead, ectoparasites like feather-feeding lice (Phthiraptera: Ischnocera) are primarily controlled by behavioral defenses such as preening. Here we test the hypothesis that birds able to preen are capable of clearing infestations of feather lice. We experimentally manipulated preening ability in a captive population of rock pigeons (Columba livia) that were infested with identical numbers of feather lice (Columbicola columbae or Campanulotes compar or both). We then monitored the feather louse infestations for 42 wk. Birds with impaired preening remained infested throughout the experiment; in contrast, the prevalence of lice on birds that could preen normally decreased by 50%. These data indicate that it is indeed possible for birds to clear themselves of feather lice, and perhaps other ectoparasites, by preening. We note, however, that captive birds spend more time preening than wild birds, and that they are less likely to be reinfested than wild birds. Thus, additional studies are necessary to determine under what circumstances wild birds can clear themselves of ectoparasites by preening.

Protection Generated by Prior Exposure to Pathogens Depends on both Priming and Challenge Dose.

Free-living hosts encounter pathogens at a wide range of frequencies and concentrations, including low doses that are largely aclinical, creating a varied landscape of exposure history and reinfection likelihood. While several studies show that higher priming doses result in stronger immunological protection against reinfection, it remains unknown how the reinfection challenge dose and priming dose interact to determine the likelihood and severity of reinfection. We manipulated both priming and challenge doses of Mycoplasma gallisepticum, which causes mycoplasmal conjunctivitis, in captive house finches (Haemorhous mexicanus), to assess reinfection probability and severity. We found a significant interaction between priming and challenge doses on reinfection probability, with the likelihood of reinfection by a high but not a low challenge dose decreasing exponentially at higher priming doses. While this interaction was likely driven by lower average infection probabilities for low-dose versus high-dose challenges, even the highest priming dose provided only negligible protection against reinfection from low-dose challenges. Similarly, pathogen loads during reinfection were significantly reduced with increasing priming doses only for birds reinfected at high but not low doses. We hypothesize that these interactions arise to some degree from fundamental differences in host immune responses across doses, with single low doses only weakly triggering host immune responses. Importantly, our results also demonstrate that reinfections can occur from a variety of exposure doses and across diverse degrees of standing immunity in this system. Overall, our study highlights the importance of considering both initial and subsequent exposure doses where repeated exposure to a pathogen is common in nature.

Managing the Health of Captive Flocks of Birds.

There are many intersecting aspects to the avicultural management of a captive flock. Extensive knowledge of the natural history of the species kept is key to fulfilling the environmental, social, nutritional, and behavioral requirements of the birds, whether in a mixed- or sole-species aviary. Species compatibility with the environment, climate, and other co-occupants plays a role as well, as does hygiene, good avicultural management, and veterinary involvement and consultation. In understanding and meeting these requirements, optimal health can be maintained through the reduction or elimination of stressors and the maintenance of normal physiologic function.

Managing Disease Outbreaks in Captive Flocks of Birds.

The modern avian practitioner may be called upon to manage disease outbreak in aviary or zoologic bird flocks. Traditionally, managing these types of disease events has been based on avicultural production principles, which may require modification to adapt to the modern leisure, educational, or exhibition aviary. We discuss how principles of avicultural medicine and disease investigation may be adapted to the aviary flock and illustrate these modified principles with real-world examples.

Paralytic and Amnesic Shellfish Toxins Impacts on Seabirds, Analyses and Management.

Marine biotoxins have been frequently implicated in morbidity and mortality events in numerous species of birds worldwide. Nevertheless, their effects on seabirds have often been overlooked and the associated ecological impact has not been extensively studied. On top of that, the number of published studies confirming by analyses the presence of marine biotoxins from harmful algal blooms (HABs) in seabirds, although having increased in recent years, is still quite low. This review compiles information on studies evidencing the impact of HAB toxins on marine birds, with a special focus on the effects of paralytic and amnesic shellfish toxins (PSTs and ASTs). It is mainly centered on studies in which the presence of PSTs and/or ASTs in seabird samples was demonstrated through analyses. The analytical techniques commonly employed, the tissues selected and the adjustments done in protocols for processing seabird matrixes are summarized. Other topics covered include the role of different vectors in the seabird intoxications, information on clinical signs in birds affected by PSTs and ASTs, and multifactorial causes which could aggravate the syndromes. Close collaboration between seabird experts and marine biotoxins researchers is needed to identify and report the potential involvement of HABs and their toxins in the mortality events. Future studies on the PSTs and ASTs pharmacodynamics, together with the establishment of lethal doses in various seabird species, are also necessary. These studies would aid in the selection of the target organs for toxins analyses and in the postmortem intoxication diagnoses.

ASSESSING THE HUMORAL RESPONSE TO AND SAFETY OF A COMMERCIALLY AVAILABLE EQUINE WEST NILE VIRUS VACCINE IN A ZOO-BASED CONSERVATION BREEDING POPULATION OF ENDANGERED GREATER SAGE-GROUSE (CENTROCERCUS UROPHASIANUS).

Greater sage-grouse (Centrocercus urophasianus) are an endangered species in Canada and have been extirpated from five states in the United States. Infectious diseases can pose a challenge to conservation efforts, and the greater sage-grouse is susceptible to West Nile virus (WNV). This study measured the humoral response to a commercially available WNV vaccine in a zoo-based conservation breeding population of greater sage-grouse. Since the initiation of the conservation program in 2014, all sage-grouse at the Calgary Zoo's Wildlife Conservation Centre have been vaccinated against WNV. Juveniles received a series of three vaccines every 2-3 wk starting around 2 wk of age; adults had received the same vaccination series at hatch and had since been boostered annually. Antibody titers were measured on 60 serum samples from 36 juveniles and 18 adults collected in 2018 using either serum neutralization or plaque-reduction neutralization methods. No detectable antibody response was noted in juveniles after their second (n = 17) or third booster vaccinations (n = 23). Only 35% of 20 adult samples collected had positive titers even after multiple years of vaccination. Only two cases of adverse vaccine reaction have been noted in this species with over 800 doses being administered between 2014 and 2020. Despite a lack of antibody response in juveniles and most adults, there have been no WNV-associated deaths in this population even with confirmed cases of WNV in free-ranging greater sage-grouse and other species in the area during this time frame, suggesting that cell-mediated immunity may be of greater importance for protection against WNV infections in this species. The initial vaccination series was changed in 2019 to a series of only two doses of vaccine, and no clinical cases or mortality from WNV occurred in 2019 or 2020 with the new protocol.

WEST NILE VIRUS SEROCONVERSION IN EASTERN LOGGERHEAD SHRIKE (LANIUS LUDOVICIANUS MIGRANS) AFTER VACCINATION WITH A KILLED VACCINE.

The loggerhead shrike (Lanius ludovicianus migrans) is a migratory songbird that has undergone massive population declines in Ontario since the 1950s. As part of a broad strategy of recovery, a captive breeding population was established in the late 1990s. This species appears to be extremely sensitive to West Nile virus (WNV) infection, with prior outbreaks at Ontario breeding facilities reaching a 100% mortality rate. This study aimed to investigate the humoral response to vaccination in juvenile birds given single versus serial booster vaccinations, as well as to assess the duration of protective virus-neutralizing titers in annually vaccinated adult birds, by measuring WNV-neutralizing antibodies via the Plaque Reduction Neutralization Test. Twenty-two adult birds and forty 18-22-day-old chicks were included in the study. Annual vaccination resulted in serum neutralizing antibody against WNV for only 59% of adult individuals 1 yr following vaccination. These results, coupled with the death of one vaccinated adult individual due to WNV infection, suggest that a second booster vaccination may be required to adequately protect adult individuals throughout the WNV transmission season. The results of the trial involving juvenile birds indicate that vaccination does not effectively stimulate the immune system of naïve juveniles to produce serum-neutralizing antibodies against WNV in the majority of tested birds, although serial booster vaccination appears to provide a level of improved seroconversion. However, the loss of 19% of naïve juveniles to natural WNV infection versus a less than 3% loss of juveniles that received at least one vaccination suggests some level of cell-mediated immunity and protection against infection takes place in juvenile birds postvaccination. The deaths of several nonvaccinated juveniles and one vaccinated adult at this study facility suggest that WNV continues to be a pathogen of high risk in this species in captivity, and likely in the wild as well.

COMPARISON BETWEEN STANDARD ZOO QUARANTINE PRACTICES AND RISK-BASED MANAGEMENT OF ANIMAL TRANSFERS: A RETROSPECTIVE ANALYSIS OF AVIAN ACQUISITION MORBIDITY AND MORTALITY (2013-2018).

Beginning 01 January 2016, for all animals transferred into the collection, Disney's Animal Kingdom used a risk-based process that relies on pathogen hazard identification and then assessment and mitigation of the risk for each identified pathogen hazard. Data on morbidity, mortality, and disease introduction was compared for birds transferred in pre- and post-risk-based processes used during the period 2013-2018. When assessing morbidity within 3 mo of acquisition, logistic regression revealed that birds entering "straight to collection" had lower morbidity rates than those entering with either "standard quarantine" or "risk-based standard quarantine" methods (P = 0.032). Mortality within 3 mo of acquisition was not significantly different between straight-to-collection and standard quarantine or risk-based standard quarantine methods (P = 0.40). In addition, no transmissible pathogens of concern were introduced with acquired birds using either method. Implementation of a risk-based approach to animal transfers between zoos and aquariums may be an alternative method that does not pose a greater risk to animal morbidity or mortality while still protecting the collection from disease introduction.

Identification and Characterization of the ATG8, a Marker of Eimeria tenella Autophagy / Identificação e Caracterização do ATG8, um marcador de autofagia em Eimeria tenella

Abstract Autophagy plays an important role in maintaining cell homeostasis through degradation of denatured proteins and other biological macromolecules. In recent years, many researchers focus on mechanism of autophagy in apicomplexan parasites, but little was known about this process in avian coccidia. In our present study. The cloning, sequencing and characterization of autophagy-related gene (Etatg8) were investigated by quantitative real-time PCR (RT-qPCR), western blotting (WB), indirect immunofluorescence assays (IFAs) and transmission electron microscopy (TEM), respectively. The results have shown 375-bp ORF of Etatg8, encoding a protein of 124 amino acids in E. tenella, the protein structure and properties are similar to other apicomplexan parasites. RT-qPCR revealed Etatg8 gene expression during four developmental stages in E. tenella, but their transcriptional levels were significantly higher at the unsporulated oocysts stage. WB and IFA showed that EtATG8 was lipidated to bind the autophagosome membrane under starvation or rapamycin conditions, and aggregated in the cytoplasm of sporozoites and merozoites, however, the process of autophagosome membrane production can be inhibited by 3-methyladenine. In conclusion, we found that E. tenella has a conserved autophagy mechanism like other apicomplexan parasites, and EtATG8 can be used as a marker for future research on autophagy targeting avian coccidia.

Resumo A autofagia desempenha um papel importante na manutenção da homeostase celular através da degradação de proteínas desnaturadas e outras macromoléculas biológicas. Nos últimos anos, muitos pesquisadores se concentraram no mecanismo da autofagia em parasitas apicomplexos, mas pouco se sabe sobre esse processo na coccidia aviária. No presente estudo, a clonagem, sequenciamento e caracterização de gene relacionado à autofagia Etatg8 foram investigados pela PCR quantitativa em tempo real (RT-qPCR), mancha ocidental (WB), ensaios indiretos de imunofluorescência (IFAs) e microscopia eletrônica de transmissão (TEM), respectivamente. Os resultados mostraram que o gene Etatg8 de E. tenella possui uma ORF de 375 bp, codificando uma proteína de 124 aminoácidos com estrutura e propriedades semelhantes à de outros apicomplexos. RT-qPCR revelou que Etatg8 é expresso durante os quatro estágios de desenvolvimento de E. tenella. Entretanto, seus níveis transcricionais foram significativamente mais elevados na fase de oocisto não esporulados. Os ensaios de manchas ocidental (WB) e de imunofluorescência (IFA) mostraram que a proteína EtATG8 foi lipidada para ligar-se à membrana do autofagossomo sob condições de deficiência nutritiva (em presença de rapamicina) e se agregar no citoplasma de esporozoítas e merozoítas. No entanto, o processo de produção de membrana do autofagossomo pode ser inibido por um inibidor de autofagia (3-meetiladeninatiladenina, 3-MA). Em conclusão, foi demonstrado que E. tenella tem um mecanismo de autofagia conservado, semelhante ao de outros parasitas apicomplexos, e que EtATG8 pode ser usado como um marcador para futuras pesquisas sobre autofagia direcionada à coccidiose aviária.

The Effects of Silymarin on Acetaminophen-Induced Acute Hepatic and Renal Toxicities in Domestic Pigeons (Columba livia).

This study evaluated the effects of silymarin on acetaminophen-induced acute liver and kidney toxicities in domestic pigeons (Columba livia). Standard colorimetric methods with commercial kits were used to measure the serum activities or levels of biomarkers associated with liver and kidney damage, such as aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, urea, uric acid, total protein, albumin, and total cholesterol, in 21 pigeons randomly assigned into 3 groups (A, B, and C). Groups A and B were administered acetaminophen 3000 mg/ kg PO q24h at the beginning of the experiment (hour 0). Group B pigeons were further treated with silymarin 35 mg/kg, starting at 12 hours after acetaminophen exposure (post-AA), with the silymarin treatment continuing q12h for 3 days. Group C pigeons served as the control group and were given tap water as the placebo. Blood was collected from the pigeons at hours 0, 12, 24, 48, and 72 of the experiment for serum biochemistry analyses. The results showed that treatment of group B pigeons with silymarin decreased the serum levels of aspartate aminotransferase, alanine aminotransferase, urea, and uric acid compared with the untreated control (group A). It also prevented decreases in serum alkaline phosphatase, total protein, albumin, and cholesterol seen in Group A. Mortality, which was 86% in the untreated control (group A), was completely prevented in group B. It was concluded that silymarin remediated the effects of acetaminophen-induced acute toxic liver and kidney injuries, which may result in pigeon mortality.

Immediate and transgenerational effects of thymol supplementation, inactivated Salmonella and chronic heat stress on representative immune variables of Japanese quail.

Environmental challenges are integrated in the inmunoneuroendocrine interplay, impacting the immune system of the challenged individuals, and potentially implying transgenerational effects on their offspring. This study addressed whether dietary supplementation with thymol can modulate the immune response of adult Japanese quail when simultaneously exposed to an inoculum of inactivated Salmonella Enteritidis and a chronic heat stress (CHS). We also evaluated whether the experienced situations by adults can affect the immune response of their undisturbed offspring. In the parental generation, supplemented quail exposed to CHS had a higher inflammatory response and similar values of the heterophil/lymphocyte (H/L) ratio than those that were not supplemented. In their offspring, those chicks whose parents were exposed to CHS showed higher inflammatory response and lower antibody production. Regarding the H/L ratio, chicks whose parents were supplemented showed lower H/L ratio values. Dietary supplementation with thymol partially and positively modulated the inflammatory response and avoided H/L ratio alteration in the parental generation exposed to high environmental temperatures, suggesting these adults were better at dealing with the challenge. The lower H/L ratio values in the offspring suggests that chicks are more capable to deal with potential stressful situations associated with conventional breeding conditions.

Differential house finch leukocyte profiles during experimental infection with Mycoplasma gallisepticum isolates of varying virulence.

Leukocyte differentials are a useful tool for assessing systemic immunological changes during pathogen infections, particularly for non-model species. To date, no study has explored how experimental infection with a common bacterial pathogen, Mycoplasma gallisepticum (MG), influences the course and strength of haematological changes in the natural songbird host, house finches. Here we experimentally inoculated house finches with MG isolates known to vary in virulence, and quantified the proportions of circulating leukocytes over the entirety of infection. First, we found significant temporal effects of MG infection on the proportions of most cell types, with strong increases in heterophil and monocyte proportions during infection. Marked decreases in lymphocyte proportions also occurred during infection, though these proportional changes may simply be driven by correlated increases in other leukocytes. Second, we found significant effects of isolate virulence, with the strongest changes in cell proportions occurring in birds inoculated with the higher virulence isolates, and almost no detectable changes relative to sham treatment groups in birds inoculated with the lowest virulence isolate. Finally, we found that variation in infection severity positively predicted the proportion of circulating heterophils and lymphocytes, but the strength of these correlations was dependent on isolate. Taken together, these results indicate strong haematological changes in house finches during MG infection, with markedly different responses to MG isolates of varying virulence. These results are consistent with the possibility that evolved virulence in house finch MG results in higher degrees of immune stimulation and associated immunopathology, with potential direct benefits for MG transmission. RESEARCH HIGHLIGHTS House finches show a marked pro-inflammatory response to M. gallisepticum infection. Virulent pathogen isolates produce stronger finch white blood cell responses. Among birds, stronger white blood cell responses are associated with higher infection severity.

Update on Avian Bornavirus and Proventricular Dilatation Disease: Diagnostics, Pathology, Prevalence, and Control.

Avian bornavirus (ABV) is a neurotropic virus that can cause gastrointestinal and/or neurologic signs of disease in birds. The disease process is called proventricular dilatation disease (PDD). The characteristic lesions observed in birds include encephalitis and gross dilatation of the proventriculus. ABV is widely distributed in captive and wild bird populations. Most birds infected do not show clinical signs of disease. This article is an update of the Veterinary Clinics of North America article from 2013: Avian Bornavirus and Proventricular Dilatation Disease: Diagnostics, Pathology, Prevalence, and Control.

Use of afoxolaner for the treatment of lice (Goniodes pavonis) in different genera (Chrysolophus spp, Lophura spp, Phasianus spp, and Syrmaticus spp) and species of pheasants and West Mexican Chachalacas (Ortalis poliocephala).

Lice are ectoparasites capable of affecting birds, and can result in direct and indirect damage to their host. Afoxolaner is an isoxazoline that has been shown to be effective against these ectoparasites without known adverse effects. The objective of this research was to evaluate the effect of afoxolaner on lice in pheasants and plain chachalacas. A total of 29 pheasants of different genera and species (Chrysolophus pictus, C. amherstiae, Lophura swinghoii, L. nycthemera, Phasianus colchicus, and Syrmaticus reevesii) and 18 West Mexican Chachalacas (Ortalis poliocephala) naturally infested with Goniodes pavonis were used. The birds were allocated to one of two groups: group 1 treated with 2.50 mg/kg of afoxolaner, and group 2 given no treatment. Ectoparasites were collected using the adhesive tape technique and identified. Afoxolaner was administered later as a single dose to group 1, and the clinical assessment to detect ectoparasites was repeated 28 days post-treatment. On day 28 post-treatment, group 1 was found to be negative for the presence of lice. The body weights were compared at the beginning and end of the clinical assessment in both groups and a significant difference in weight of treated birds was found. The mean body weight decreased by 0.017 g in control group, whereas it increased by 0.016 g in treated group. Oral administration of afoxolaner is an effective option for the treatment of Goniodes pavonis infestations in zoo birds.

Is Allopreening a Stimulus-Driven Defense Against Ectoparasites?

Allopreening occurs when 1 bird preens another bird. The behavior is normally directed at the head and neck of the recipient, i.e., regions that the bird cannot self-preen. Studies of penguins, pigeons, and other groups of birds suggest that allopreening plays a role in the control of ectoparasites, such as ticks and feather lice. However, it is not known whether allopreening increases in response to increases in parasite load, or whether it is a programmed response that occurs independently of parasite load. We conducted a laboratory experiment using wild-caught rock pigeons (Columba livia) to test the relationship between ectoparasite load and allopreening rate. We added feather lice (Columbicola columbae) to captive pigeons and tested for changes in allopreening rates compared to control birds with no lice added. Allopreening rates did not change in response to the addition of lice. Interestingly, however, our data revealed a negative correlation between allopreening and self-preening rates.

Phylogeny, pathogenicity and transmissibility of a genotype XII Newcastle disease virus in chicken and goose.

Although Newcastle disease virus (NDV) has a worldwide distribution, some NDV genotypes have more regional geographical ranges within continents. In this study, we isolated a subgenotype XIIb NDV strain, Goose/CH/GD/E115/2017 (E115), from geese in Guangdong province, Southern China, in 2017. Phylogenetic analysis showed that E115 and six other NDVs from geese in China were grouped under subgenotype XIIb and were distinct from subgenotype XIIa, isolated from chickens in South Africa, and subgenotype XIId, isolated from chickens in Vietnam. To better understand the pathogenicity and transmission of the subgenotype XIIb NDVs from geese in Guangdong province, we inoculated chickens and geese with 106 EID50 of the E115 virus. Eight hours after inoculation, three naïve chickens and three naïve geese were co-housed with the infected chickens or geese to assess intraspecific and interspecific horizontal transmission of the E115 virus. The E115 virus induced significant clinical signs without mortality in chickens, while it was not pathogenic to geese. Intraspecific and interspecific horizontal transmission of the E115 virus was observed among chickens and geese via direct contact. Furthermore, although the current vaccines provided complete protection against disease in chickens after challenging them with the E115 virus, the virus could also be transmitted from vaccinated chickens to naïve contact chickens. Collectively, our findings highlight the need for avoiding the mixing of different bird species to reduce cross-species transmission and for surveillance of NDV in waterfowl.

Assembly of pigeon circovirus-like particles using baculovirus expression system.

Pigeon circovirus (PiCV) is able to infect racing and meat pigeons of all ages and is a key factor that triggers young pigeon disease syndrome (YPDS). PiCV vaccine research has been impeded because PiCV cannot be grown or propagated in cell cultures. Virus-like particles (VLPs), which can be generated by a wide range of expression systems, have been shown to have outstanding immunogenicity and constitute promising vaccines against a wide range of pathogens. Cap protein, which contains neutralizing antibody epitopes, is the only capsid protein of PiCV. In this study, the baculovirus expression system was utilized to express the PiCV Cap protein, which was self-assembled into VLPs with a spherical morphology and diameters of 15-18 nm. Specific antibodies against the Cap protein were induced after BALB/c mice immunized intramuscularly (i.m.) with VLPs combined with adjuvant. Based on these findings, PiCV VLPs may be a promising candidate vaccine against PiCV.

Recombinant Modified Vaccinia Virus Ankara (MVA) Vaccines Efficiently Protect Cockatiels Against Parrot Bornavirus Infection and Proventricular Dilatation Disease.

Parrot bornaviruses (PaBVs) are the causative agents of proventricular dilatation disease (PDD), a chronic and often fatal neurologic disorder in Psittaciformes. The disease is widely distributed in private parrot collections and threatens breeding populations of endangered species. Thus, immunoprophylaxis strategies are urgently needed. In previous studies we demonstrated a prime-boost vaccination regime using modified vaccinia virus Ankara (MVA) and Newcastle disease virus (NDV) constructs expressing the nucleoprotein and phosphoprotein of PaBV-4 (MVA/PaBV-4 and NDV/PaBV-4, respectively) to protect cockatiels (Nymphicus hollandicus) against experimental challenge infection. Here we investigated the protective effect provided by repeated immunization with either MVA/PaBV-4, NDV/PaBV-4 or Orf virus constructs (ORFV/PaBV-4) individually. While MVA/PaBV-4-vaccinated cockatiels were completely protected against subsequent PaBV-2 challenge infection and PDD-associated lesions, the course of the challenge infection in NDV/PaBV-4- or ORFV/PaBV-4-vaccinated birds did not differ from the unvaccinated control group. We further investigated the effect of vaccination on persistently PaBV-4-infected cockatiels. Remarkably, subsequent immunization with MVA/PaBV-4 and NDV/PaBV-4 neither induced obvious immunopathogenesis exacerbating the disease nor reduced viral loads in the infected birds. In summary, we demonstrated that vaccination with MVA/PaBV-4 alone is sufficient to efficiently prevent PaBV-2 challenge infection in cockatiels, providing a suitable vaccine candidate against avian bornavirus infection and bornavirus-induced PDD.

Antimicrobial peptide, cLF36, affects performance and intestinal morphology, microflora, junctional proteins, and immune cells in broilers challenged with E. coli.

This study investigated the effects of an antimicrobial peptide (AMP), cLF36, on growth performance and the histophysiological changes of the intestine in E. coli-challenged broiler chickens. A total number of 360 day old male chicks were randomly assigned to 4 groups of 6 replicates as follows: T1) negative control diet based on corn-soybean meal without E. coli challenge and additives; T2) positive control diet based on corn-soybean meal and challenged with E. coli without any additives; T3) positive control diet challenged with E. coli and supplemented with 20 mg AMP (cLF36)/kg diet; T4) positive control diet challenged with E. coli and supplemented with 45 mg antibiotic (bacitracin methylene disalicylate)/kg diet. Results showed that T3 improved growth performance and the jejunal morphology of E. coli-challenged chickens similar to those of T4. While antibiotic non-selectively decreased the population of ileal bacteria, AMP increased the population of Lactobacillus spp. and decreased harmful bacteria in the ileum of E. coli-challenged chickens. Supplementing E. coli-challenged chickens with AMP improved the gene expression of immune cells and upregulated the expression of tight junction proteins compared to other challenged groups. In conclusion, although cLF36 beneficially affected growth performance and the intestinal morphology of E. coli-challenged chickens similar to those of the antibiotic group, this AMP drastically improved the intestinal microbiome, immune cells, and junctional proteins compared to other E. coli-challenged birds, and can be nominated as an alternative for growth promoter antibiotics.