Poultry

Limited published data are available on the ratio of digestible non-essential amino acid (DNEAA) to digestible lysine (DLys) for layers. The effect of different DNEAA-to-DLys ratios on performance parameters of Hy-Line Silver-Brown layers was studied from 20 to 35 weeks. Experimental design was randomized with ten dietary treatments of increasing concentrations of DNEAA-to-DLys ratio (10.61, 10.84, 11.08, 11.31, 11.54, 11.77, 12.00, 12.23, 12.46, 12.69). Average daily feed intake, total feed intake, laying rate, cumulative egg number, egg weight, hen body weight, feed conversion ratio, egg mass output, albumen weight, eggshell weight, yolk weight, eggshell breaking strength, eggshell thickness, carcass and feather weight, carcass protein, carcass fat, liver weight, and liver fat were recorded. Changing the DNEAA/DLys ratio did not affect production parameters. Yolk and yolk-to-egg weight decreased with an increase in DNEAA/DLys ratio, while albumen-to-yolk and albumen-to-egg weight increased. The DNEAA/DLys ratio did not affect carcass or liver composition, but liver and liver-to-body weight (%) decreased as the DNEAA/DLys ratio increased. Hy-Line Silver-Brown layers during peak production sustained egg production and quality even on the lowest ratio in this study. Low DNEAA/DLys ratios increased liver fat deposition. Full article

This study evaluated the effects of limestone particle size and 25-hydroxycholecalciferol supplementation on performance, egg quality, digestive organ biometrics, bone characteristics, thermoregulatory responses, and behavior of brown laying hens reared under hot environmental conditions. The trial lasted five periods of 28 days. A total of 270 Lohmann Brown Lite hens (48 weeks old) were allocated in a completely randomized design with a 2 × 2 + 1 factorial arrangement, comprising two limestone particle sizes (MGD 0.568 mm and MGD 1.943 mm) and two supplementation levels of vitamin D (2760 IU and 1380 IU), plus a control diet, totaling five treatments with six replicates each. The dietary treatments were as follows: (1) control diet without vitamin D supplementation; (2) 250 g vitamin D with 100% fine limestone; (3) 125 g vitamin D with 100% fine limestone; (4) 250 g vitamin D with 50% fine + 50% coarse limestone; and (5) 125 g vitamin D with 50% fine + 50% coarse limestone. Productive performance, egg quality, organ biometrics, bone traits, thermoregulatory variables, and behavioral indicators were measured. Data were analyzed by ANOVA, followed by Tukey test (5%), considering the factorial model. There was no interaction between the factors for any parameter evaluated. There was an effect of shift on thermoregulatory variables. The other variables were not influenced by the treatments. These findings indicate that the tested limestone particle sizes can be incorporated in the diets of brown laying hens without affecting performance, egg quality, bone integrity, thermoregulation, or behavior, regardless of vitamin D supplementation, under hot climatic conditions. Full article

Bidens pilosa L. extract (BPE), a traditional medicine known for its antimicrobial properties, has not been thoroughly investigated for its potential against avian pathogenic Escherichia coli (APEC), a major pathogen responsible for severe economic losses and high mortality in poultry. This study aimed to comprehensively assess the antibacterial activity of BPE against APEC through both in vivo and in vitro experiments and to explore its underlying mechanisms. In a chicken infection model, BPE treatment led to an 80% cure rate and 20% mortality, in contrast to the 90% diarrhea and 70% mortality observed in the untreated model group. BPE also significantly alleviated intestinal tissue damage and reduced serum levels of inflammatory cytokines IL-6 and IL-1β (p < 0.01). In vitro analyses revealed a minimum inhibitory concentration (MIC) of 625 mg/mL. BPE dose-dependently suppressed bacterial motility, swarming, and biofilm formation (p < 0.01) and markedly increased membrane permeability, indicated by elevated release of nucleic acids, proteins, and alkaline phosphatase (p < 0.001). Moreover, PCR results showed that treatment with BPE at 1/2 MIC for 24 h significantly downregulated multiple virulence-associated genes, including aatA, papC, ibeB, vat, ompA, iss, fyuA, and irp2 (p < 0.01). These results demonstrate that BPE exerts its anti-APEC effects by damaging cell membrane integrity, inhibiting biofilm formation and motility, and suppressing virulence gene expression. Our findings support the potential of BPE as a natural alternative for controlling APEC infections and contribute a scientific basis for the use of traditional herbal medicine in combating bacterial diseases. Full article

The emergence of antimicrobial resistance (AMR) across the broiler production chain holds significant economic, animal, and public health implications. This study investigated phenotypic resistance to 13 antimicrobials and the presence of 35 antimicrobial resistance genes (ARGs) in Escherichia coli (n = 291) isolated across three broiler production chains (broiler breeder farms, hatcheries, commercial broiler farms, and retail meat shops). An extremely high phenotypic resistance (>70%) to doxycycline, ciprofloxacin, and cefpodoxime, and very high resistance (50–70%) to ampicillin, cefotaxime, gentamicin, and ceftazidime was observed. In addition, 97% of isolates were multidrug-resistant (resistant to ≥1 drug in ≥3 antimicrobial classes), 42% were extended-spectrum beta-lactamase (ESBL) producers, 65% were resistant to third-generation cephalosporins (3GCR), and 21% were resistant to colistin. The Poisson regression model revealed no significant difference in AMR among broiler production stages, except for colistin. Among 35 ARGs tested, 24 (67%) were detected at least once. The most prevalent were tetA, bla_TEM, qnrB, qnrS, and aac(6′)-Ib-cr, while qnrD, sul2, bla_OXA, and bla_CTX-M were detected at lower levels (1–7%). All five tested mcr genes (mcr-1 to mcr-5) were identified in commercial farms and retail shops. No bla_NDM, tetB, tetC, tetD, tetM, qnrC, aac(3)-IIa (aacC2), aph(3)-IIa (aphA2), or aac(6′)-Ib genes were found. A strong correlation was observed between AMR phenotypes and ARGs. High AMR among E. coli in broiler production poses significant One Health risks, with widespread MDR, ESBL production, and resistance to critically important antimicrobials. Prudent antimicrobial use, enhanced surveillance and education, farm biosecurity, and One Health strategies are crucial in mitigating these threats. Full article

The increasing demand for sustainable and cost-effective animal feed alternatives has stimulated the use of agro-industrial by-products in poultry diets. This study evaluated the effects of tambaqui (Colossoma macropomum) residual oil (TRO), derived from aquaculture waste, on productive performance, physiological responses, and egg quality in commercial laying hens. A total of 144 Hisex Brown hens were assigned to diets containing 0%, 1.5%, 3.0%, or 4.5% TRO for 63 days. While TRO inclusion did not affect overall productivity, moderate levels (1.5% and 3.0%) improved egg weight, yolk pigmentation, and internal quality (Haugh unit). Hematological and biochemical parameters indicated metabolic adaptations, with increased cholesterol and decreased triglycerides in treated groups. The yolk fatty acid profile revealed higher omega-3 content with TRO inclusion, but lipid oxidation (TBARS) also increased, especially at higher levels. Sensory evaluation showed reduced aroma and flavor acceptability in eggs from hens fed 3.0% and 4.5% TRO. These findings suggest that moderate TRO inclusion can enhance egg nutritional value and support sustainable aquaculture waste reuse, though excessive levels may compromise product acceptability. Optimal inclusion levels should be further explored to balance metabolic benefits, oxidative stability, and consumer preferences. Full article

Following restrictions on antibiotic growth promoters in poultry production, there is growing interest in natural feed additives that support health and productivity. Among these, black cumin (Nigella sativa) has emerged as a promising candidate due to its antioxidant, antimicrobial, and immunomodulatory properties. Most studies report that black cumin, in the form of whole seeds, seed meal, or seed oil, improves body weight gain and feed conversion ratio, enhances antioxidant and immune status, and provides additional benefits on lipid profiles, liver enzymes, and cecal microbial balance. This review provides a focused synthesis of recent studies (2014–2025) on black cumin supplementation in broiler chickens, considering its various forms (whole seeds, seed meal, seed oil, and nano-formulations) and production contexts (healthy, heat-stressed, and disease-challenged birds). Specifically, this review compares responses across different forms and doses, evaluates effects on growth performance, immune function, gut health, antioxidant status, liver metabolism, and meat and carcass quality, and highlights inconsistencies among studies. Additionally, it identifies key research gaps to guide future investigations, including optimal dosing, long-term safety, and practical applications in commercial production. Overall, black cumin shows potential as a natural alternative to antibiotics, but further standardized, large-scale studies are needed to confirm its efficacy and feasibility in sustainable poultry farming. Full article

Animal welfare (AW) is increasingly being discussed and mandated in chicken production, both by current Brazilian legislation and by importing markets. Industries continually seek greater financial returns, and within this context, it has been observed that the proper implementation of animal welfare principles effectively reduces losses by minimizing carcass condemnations due to injuries, thereby significantly contributing to in-creased profitability. The economic impact of non-compliance with these welfare standards in broiler production is well documented in the scientific literature. However, the same level of concern is not observed regarding the financial impact on integrated producers, who supply the raw materials. The present study aims to systematically map, contextualize, quantify, and qualitatively analyze articles evaluating the implementation of animal welfare in industrial broiler production and its impact on the financial returns of producers and integrated companies. The primary descriptor used was “animal welfare.” To quantify the relevant articles, the Proknow-C method was applied, followed by a similarity analysis using VoSViewer® software version 1.6.19 for systematic content evaluation. Descriptor combinations were led by animal welfare, followed by broiler pro-duction, poultry production, slaughter, economy, and rural producers. Although a significant number of articles address AW, those focused exclusively on chicken production are far fewer, declining even more when carcass condemnations are considered. Only six studies included the descriptor “economic,” and just three included “producer.” The con-tent of these nine studies was systematically reviewed, with two excluded and seven selected for discussion. Among the seven analyzed studies, none specifically examined the economic impact of AW implementation for the producer, clearly highlighting a significant research gap. Full article

This study determined the efficacy of in-feed supplementation of a medium-chain fatty acid, caprylic acid (CA), on the cecal colonization of multidrug-resistant (MDR) Salmonella Heidelberg (SH) and its effect on the cecal microbiome of commercial broilers. A total of 24, 4-week-old commercial Ross 708 chickens were randomly allocated to two replicates of four treatment groups in eight BSL2 isolators (3 birds/isolator): Negative control (NC), Positive Control (PC), Antibiotic group (AB), and caprylic acid (CA) groups. The birds received a Salmonella-free standard corn–soy-based diet, with the broilers in the AB receiving 50 g/ton bacitracin methylene disalicylate, and the CA group receiving caprylic acid (1% w/w), in feed from days 1 to 35. All birds, except those in the NC group, were challenged with ~3.7 log₁₀ CFU of MDR SH/5 mL by crop gavage on day 29. Cecal samples were collected 7 days after the challenge for SH recovery by direct plating and enrichment, as well as for DNA extraction for 16S rRNA gene amplicon sequencing. Compared to the PC group, a 3.6 log₁₀ CFU/g reduction in SH was observed in the CA group (p < 0.05). Although no significant effect of CA on cecal microbial composition was observed, a significant difference in taxonomic α- and β-diversities was observed in the AB. CA also resulted in significant differences in hub taxa compared to PC in the network association analysis, indicating a potential role for microbiome modulation in its mechanism of action. Full article

Backyard poultry systems (BPS) are the most widespread form of animal production worldwide, contributing to household economies and improving food availability. However, limited biosecurity measures and close human–animal interactions raise concerns regarding zoonotic disease transmission. In recent years, consumer-driven motivations have given rise to non-traditional BPS with differential attributes (BPS-DA), yet there is limited knowledge about their food production practices. This study aimed to characterize and compare practices across 25 BPS and 25 BPS-DA in the Metropolitan Region using surveys, interviews, and direct observations of egg collections and poultry slaughters. Eggs were the main animal product in both systems, with women primarily responsible for care. Poultry slaughter was reported exclusively in BPS (60%), generally performed under inadequate hygienic conditions and without veterinary oversight. These practices, (poultry slaughter, food production and handling), may considerably increase the risk of human exposure to zoonotic pathogens, such as avian influenza viruses. In contrast, BPS-DA prioritized birds as companion animals (60%), free-range rearing (68%), and hobby-based production (80%). While both systems showed limited biosecurity, significant differences were found in the use of dedicated footwear (p = 0.01; V = 0.35), egg collection sites (p = 0.04; V = 0.29), and refrigeration (p = 0.004; V = 0.41). Veterinary access was limited in both (32% in BPS; 44% in BPS-DA). These findings highlight critical gaps in health management and underscore the need for context-specific educational and regulatory strategies for safer backyard poultry production. Full article

Fowl adenovirus (FAdV) can cause different poultry diseases with economic losses in the broilers and layers commercial farms. FAdV is currently classified into five species and 12 serotypes, disseminated in poultry flocks worldwide. The present study aimed to identify FAdV species and serotypes in Brazilian poultry farms. A total of 678 chicken flocks from the main Brazilian poultry-producing regions were evaluated for FAdV infection between 2020 and 2023. FAdV was detected by a real-time PCR targeting 52K gene and further genotyped by partial sequencing of the hexon gene followed by phylogenetic analyses. The results demonstrated that FAdV was detected in 72 flocks (10.6%). In 46 of these samples, FAdV species and serotypes could be identified, including three main species: Aviadenovirus ventriculi (FAdV-A = 15), Aviadenovirus gallinae (FAdV-D = 15) and Aviadenovirus hepatitidis (FAdV-E = 16). Phylogenetic analysis based on 173 partial hexon sequences (including sequences from this study, 44 previously sequenced in Brazil, and 86 data from other countries) revealed five separate clades for FAdV species. All Brazilian FAdVs were classified into the same three species reported above (FAdV-A = 19, FAdV-D = 34, FAdV-E = 37), and also in well-supported subclades for each serotype: FAdV-A1 (n = 19), FAdV-D9 (n = 1), FAdV-D11 (n = 33), FAdV-E6 (n = 1), FAdV-E8a (n = 33), FAdV-E8b (n = 3). Amino acid substitutions in the hyper variable regions (1, 2 and 3) and conserved motifs of the Hexon protein were further analyzed, enabling discrimination between closely related serotypes. This study demonstrates the circulation of different FAdVs in Brazil, highlighting FAdV-A1, FAdV-D9, FAdV-D11, FAdV-E6, FAdV-E8a and FAdV-E8b. The findings reported here also indicate genetic and amino acid diversity in the Hexon protein of the FAdVs in Brazilian poultry farms, which are of importance for molecular surveillance and poultry diseases control strategies. Full article

The interaction between gut microbiota and C. jejuni in the guts of broiler chickens is essential for the bacterium’s growth and potential pathogenicity. Recent findings highlighted the significance of modifying gut microbiota in relation to higher C. jejuni colonization rates and improved immune responses. This study suggested that a varied and balanced microbiota aids in decreasing and preventing C. jejuni proliferation via mechanisms including competitive exclusion, the synthesis of antimicrobial peptides, and the modulation of the chicken immune response. C. jejuni demonstrates adaptability in the gut environment by encouraging the growth of beneficial bacteria while inhibiting others, improving the way it acquires nutrients, and modifying the transcriptional response of its virulence factors. The dynamic nature of these microbiota communities has caused differences in the results of how gut microbiota and C. jejuni proliferation interact. Understanding the relationships between gut microbiota and C. jejuni is critical for developing strategies to mitigate the impact of C. jejuni in broiler chickens. This review compiles information on the relationships between gut microbiota and C. jejuni proliferation in broiler chickens and offers commentary on how the findings could improve gut health and food safety. Full article

Keel bone lesions (KBLs) represent a relevant welfare concern in laying hens, arising from complex interactions among genetics, housing systems, and management practices. This study presents the development of an image analysis system for the automated detection and classification of KBLs in slaughterhouse videos, enabling scalable and retrospective welfare assessment. In addition to lesion classification, the system can track and count individual carcasses, providing estimates of the total number of specimens with and without significant lesions. Videos of brown laying hens from a commercial slaughterhouse in northeastern Italy were recorded on the processing line using a smartphone. Six hundred frames were extracted and annotated by three independent observers using a three-scale scoring system. A dataset was constructed by combining the original frames with crops centered on the keel area. To address class imbalance, samples of class 1 (damaged keel bones) were augmented by a factor of nine, compared to a factor of three for class 0 (no or mild lesion). A YOLO-based model was trained for both detection and classification tasks. The model achieved an F1 score of 0.85 and a mAP@0.5 of 0.892. A BoT-SORT tracker was evaluated against human annotations on a 5 min video, achieving an F1 score of 0.882 for the classification task. Potential improvements include increasing the number and variability of annotated images, refining annotation protocols, and enhancing model performance under varying slaughterhouse lighting and positioning conditions. The model could be applied in routine slaughter inspections to support welfare assessment in large populations of animals. Full article

Enterococci, commonly found in the normal intestinal flora of humans and animals, have emerged as an important human pathogen. A total of 184 isolates (88 isolates in 2015 and 96 isolates in 2016) were collected from 46 flocks. Two predominant enterococcus species were identified: Enterococcus faecalis (59%) and Enterococcus faecium (~39%). Resistance to penicillin was significantly decreased in the overall enterococci community, while it remained unchanged in the multi-class drug resistant (MDR) community. We identified the emeA and efrAB genes, which encode efflux pump systems, in 93% (26/28) of the MDR isolates with (intermediate) resistance to levofloxacin. The ermB gene was present in all MDR strains with resistance to erythromycin. The lsa gene was detected in 87% (84/97) of the MDR isolates with resistance to quinupristin/dalfopristin. About 82.2% of MDR strains in 2015 and 100% of MDR strains in 2016 carried the insertion sequence IS256, which is known to be associated with AMR genes, conferring resistance to erythromycin, gentamicin and vancomycin in enterococci. These results support the need for monitoring AMR in Gram-positive bacteria in poultry production, specifically in broiler chicken farms, to complement current AMR data, and develop a timely intervention framework. Full article

A 28-day study involving 448 male Ross 308 broilers aimed to determine the effect of dietary rice bran (RB) and xylanase (XYL) in maize- and wheat-based diets on chicken growth, N-corrected apparent metabolizable energy (AMEn), and nutrient availability. Two isonitrogenic and isocaloric maize- or wheat-based basal diets (BDs) were formulated matching breeding recommendations. Each diet was then split in four parts: two parts BD was substituted with 75 g/kg RB and then one of the RB substituted and one of the original parts was supplemented with 16,000 XYL units/kg, resulting in a total of eight experimental dietary treatments. Each diet was fed to seven pens of eight birds per pen following randomization. The data were analyzed by ANOVA using a 2 × 2 × 2 factorial design (cereal type × RB × XYL). Enzyme supplemented RB-free wheat-based diet had greater AMEn (p = 0.002) and fiber digestibility (p = 0.007) compared to the rest. Feeding RB reduced daily feed intake (p = 0.015) and weight gain (p < 0.001) of chicks. Birds fed wheat-based diets had greater feed efficiency, coupled with an increase in starch digestibility (SD) and energy conversion ratio (ECR). The observed differences in feed efficiency were explained only by SD and ECR. Full article

Newcastle Disease (ND) is an important and notable disease among the avian infectious diseases, because of its high contagiousness, and the most virulent strains of ND virus (NDV) have impacted poultry breeders all over the world. Immunization and biosecurity measures are used to reduce ND; however, vaccination has been shown to offer protection against clinical signs but not against virus proliferation and shedding, which could have an adverse effect on the environment. The genetic basis for inherent resistance to NDV has been established, and genetic selection on existing resistance-related genetic variation can help to mitigate virus propagation. Further, understanding the genes and processes that drive the response to NDV will lay the groundwork for genetic improvement in poultry. The majority of studies on NDV susceptibility make use of phenotypic indicators such as body weight, morbidity, mortality, antibody response, and viral load. According to recent advancements in molecular genetic research, many different genes are diversely regulated in different chicken lines to NDV infection, which might be used in the future to establish disease-resistant breeding approaches. It is possible that many more genes linked to illness and resistance are still to be discovered, because the precise mechanism of resistance is not entirely understood. The enhanced genetic knowledge of chickens and the development of more advanced transgenic techniques would lead to pathogen resistance. Hence, this paper summarizes the current understanding of genetic resistance to Newcastle Disease, and we additionally highlight a few possible genes/markers connected with NDV that may improve chicken resistance to NDV infections and can be used to produce NDV-resistant chicken breeds/strains in the near future. Full article

Antimicrobial resistance (AMR) constitutes a serious public health issue, and the European Union (EU) requires reduction in the sales of antibiotics in farmed animals of 50% by 2030. A scoping review was conducted in PubMed for the years from 2000 to 2024, limited to the English and German languages, with the aims to (1) provide an overview of factors on commercial poultry farms potentially associated with health-related endpoints such as mortality, disease prevalence, carcass condemnation, performance as well as AMR/antimicrobial usage at different hierarchical levels (animal, flock/batch, stable, farm), and (2) identify inconsistencies with respect to these potential risk factors. Overall, 34 peer-reviewed publications met the inclusion criteria for the review. Significant associations identified in the uni- or multivariable statistical analysis were summarised using graphs and bar charts. The results highlight that risk factor–outcome associations often are complex, inconsistent with regards to the direction of the influence especially for some ordinal or categorical variables. In some associations such as the sex of the animals and performance, contrary directions were reported in different studies—illustrating the multifactorial dynamics of commercial poultry production. This research enhances the understanding of the complexity of commercial poultry production, which is essential when designing future studies and interpreting their results. Full article

Understanding how environmental conditions affect broiler comfort across different seasons is crucial for enhancing welfare in commercial poultry production. This study aimed to identify the relationship between housing environment, litter conditions, and broiler discomfort at different growth stages using data collected from two flocks reared during winter and summer. Environmental variables (temperature, humidity, ammonia, pH, and CO₂) and broiler responses were recorded and analyzed weekly. Discomfort was defined as a binary variable based on threshold deviations in temperature and air quality. Non-parametric statistical tests and a Random Forest model were employed to explore associations and predict comfort status. Results showed that discomfort was significantly higher during winter, particularly in weeks 1 and 6, likely due to thermal instability and rising ammonia levels. Summer flocks exhibited more stable comfort profiles. The predictive model achieved a high test accuracy (97.1%) and identified broiler weight, ammonia, and temperature as the strongest predictors of discomfort. Weekly discomfort patterns and feature importance analyses revealed critical intervention points and variables. These findings provide actionable insights for automating welfare monitoring in commercial broiler production, offering valuable information for season-specific management strategies and demonstrating the potential for integrating predictive models into automated welfare monitoring systems to support precision livestock farming. Full article

Optimal commercial conditions have been shown to improve the performance and meat yield of broilers. Also, dietary 25-hydroxycholecalciferol (25OHD₃; crystalline form) has not shown a negative impact on chicken health when it was fed at 10 times (10×) higher than 69 μg/kg. The objectives of this study were to determine the effects of up to 8 times (8×) higher than the commercial level (69 μg/kg of feed) of dietary 25OHD₃ on the performance, breast meat yield, and serum 25OHD₃ concentration of broilers. Eighteen male chicks were randomly assigned to each of 20 pens within each of the two dietary treatments. Treatments were commercial diets containing 250 IU/kg of vitamin D₃ (control) for the starter [(0 to 14 days post-hatch (poh), grower (15 to 28 poh), and finisher (29 to 42 poh) dietary phases; or diets containing Hy-D (water-soluble source of 25OHD₃) that consisted of 552 (8×) μg/kg of 25OHD₃ for the starter, 276 (4×) μg/kg of 25OHD₃ for the grower, and 34.5 (0.5×) μg/kg of 25OHD₃ for the finisher dietary phases. Live performance variables as well as serum 25OHD₃ concentrations were measured in each dietary phase. At 14, 28, and 39 poh, breast meat yield that included pectoralis major (P. major) and pectoralis minor (P. minor) muscle weights was determined in ten replications per dietary treatment. Breast yield was also calculated by adding the values of the P. major and P. minor muscles. From 14 to 42 poh, the Hy-D diets decreased (p < 0.0001) broiler body weight (BW) and BW gain and increased (p < 0.0001) total mortality and feed conversion ratio in comparison to control treatment groups. In addition, birds fed Hy-D diets had significantly (p < 0.0001) lower P. major and breast meat yields from 14 to 39 poh as compared to those birds fed the control diet. Serum 25OHD₃ concentration was significantly (p < 0.0001) higher (10×) in birds that belonged to the Hy-D diet treatment than those in the control diet treatment group. These results indicate that the disproportionally high (8×) level of dietary 25OHD₃ resulted in detrimental effects on the performance and meat yield of broilers. A reduction in both performance and meat yield of broilers in response to the elevated level of dietary 25OHD₃ may have been due to vitamin D₃ toxicity, which can result in an association with the overproduction of the active form of the vitamin in response to elevated serum concentrations of 25OHD₃. Full article

To determine if exposing embryos to light during incubation affects antibody titer and corticosterone immediately following hatch, we incubated layer eggs and exposed them to light or darkness and vaccinated a subset of each treatment against Newcastle Disease Virus (NDV) using in ovo administration on ED 18, spray application at hatch (d 0), or not at all. There were six treatments: light incubated and non-vaccinated (LNV), light incubated and in ovo vaccinated (LIV), light incubated and post-hatch vaccinated (LPHV), dark incubated and non-vaccinated (DNV), dark incubated and in ovo-vaccinated (DIV), and dark incubated and post-hatch vaccinated (DPHV). Plasma corticosterone (CORT) and NDV antibody titers were measured on d 0, 7, and 14. Light-incubated chicks had lower (p < 0.05) plasma CORT on d 0. NDV titers did not differ (p > 0.05) between light- and dark-incubated chicks on d 0, 7, or 14. However, LIV chicks had higher antibody titers than LPHV on d 14. Exposing embryos to continuous green light during incubation may reduce stress during the early post-hatch period. Vaccination method, rather than exposure to continuous green light during incubation, may have a greater impact on humoral immune response post-hatch. Full article