Genomic Regions and Candidate Genes Affecting Response to Heat Stress with Newcastle Virus Infection in Commercial Layer Chicks Using Chicken 600K Single Nucleotide Polymorphism Array.

Heat stress results in significant economic losses to the poultry industry. Genetics plays an important role in chickens adapting to the warm environment. Physiological parameters such as hematochemical parameters change in response to heat stress in chickens. To explore the genetics of heat stress resilience in chickens, a genome-wide association study (GWAS) was conducted using Hy-Line Brown layer chicks subjected to either high ambient temperature or combined high temperature and Newcastle disease virus infection. Hematochemical parameters were measured during three treatment phases: acute heat stress, chronic heat stress, and chronic heat stress combined with NDV infection. Significant changes in blood parameters were recorded for 11 parameters (sodium (Na+, potassium (K+), ionized calcium (iCa2+), glucose (Glu), pH, carbon dioxide partial pressure (PCO2), oxygen partial pressure (PO2), total carbon dioxide (TCO2), bicarbonate (HCO3), base excess (BE), and oxygen saturation (sO2)) across the three treatments. The GWAS revealed 39 significant SNPs (p < 0.05) for seven parameters, located on Gallus gallus chromosomes (GGA) 1, 3, 4, 6, 11, and 12. The significant genomic regions were further investigated to examine if the genes within the regions were associated with the corresponding traits under heat stress. A candidate gene list including genes in the identified genomic regions that were also differentially expressed in chicken tissues under heat stress was generated. Understanding the correlation between genetic variants and resilience to heat stress is an important step towards improving heat tolerance in poultry.

Prevalence of vision zero action plans or strategies: USA, 2021.

BACKGROUND: Vision Zero is a strategy to eliminate traffic fatalities and to promote equitable mobility options for all road users. Using a nationally representative survey, we aimed to estimate the prevalence of Vision Zero action plans or strategies in the USA. METHODS: Municipal officials were surveyed in 2021. In this cross-sectional study, we calculated the prevalence of Vision Zero plans or strategies and compared municipalities with adjusted prevalence ratios (PR) to account for region and sociodemographic characteristics. RESULTS: Among 1955 municipalities participating in the survey (question-specific response rate: 44.3%), the prevalence of a Vision Zero action plan or strategy was 7.7%; 70.5% responded no and 21.8% don't know. Prevalence was 4.8% in small municipalities (1000-2499 residents), 20.3% in medium-large municipalities (50 000-124 999 residents; PR=4.1), and 37.8% in large municipalities (≥125 000 residents; PR=7.6). CONCLUSION: The prevalence of Vision Zero plans and strategies across the USA is low. Additional adoption of Vision Zero plans and strategies could help address traffic fatalities.

Current challenges and future of agricultural genomes to phenomes in the USA.

Dramatic improvements in measuring genetic variation across agriculturally relevant populations (genomics) must be matched by improvements in identifying and measuring relevant trait variation in such populations across many environments (phenomics). Identifying the most critical opportunities and challenges in genome to phenome (G2P) research is the focus of this paper. Previously (Genome Biol, 23(1):1-11, 2022), we laid out how Agricultural Genome to Phenome Initiative (AG2PI) will coordinate activities with USA federal government agencies expand public-private partnerships, and engage with external stakeholders to achieve a shared vision of future the AG2PI. Acting on this latter step, AG2PI organized the "Thinking Big: Visualizing the Future of AG2PI" two-day workshop held September 9-10, 2022, in Ames, Iowa, co-hosted with the United State Department of Agriculture's National Institute of Food and Agriculture (USDA NIFA). During the meeting, attendees were asked to use their experience and curiosity to review the current status of agricultural genome to phenome (AG2P) work and envision the future of the AG2P field. The topic summaries composing this paper are distilled from two 1.5-h small group discussions. Challenges and solutions identified across multiple topics at the workshop were explored. We end our discussion with a vision for the future of agricultural progress, identifying two areas of innovation needed: (1) innovate in genetic improvement methods development and evaluation and (2) innovate in agricultural research processes to solve societal problems. To address these needs, we then provide six specific goals that we recommend be implemented immediately in support of advancing AG2P research.

Changes in Perceptions of the Near-Home Walking Environment Among US Adults-2015 and 2020 National Health Interview Survey.

BACKGROUND: The built environments in which we work, live, and play can influence physical activity behaviors, and perceptions of these environments are associated with walking behavior. This study's objective is to compare national-level data on perceptions of the near-home walking environment from the 2015 and 2020 National Health Interview Survey. METHODS: Adults in 2015 (n = 30,811) and 2020 (n = 29,636) reported perceptions of walkable supports (roads, sidewalks, paths, or trails; sidewalks on most streets), destinations (shops, stores, or markets; bus or transit stops; movies, libraries, or churches; places that help you relax, clear your mind, and reduce stress), and barriers to walking (traffic; crime; animals). Age-adjusted prevalence estimates, prevalence differences, and 95% confidence intervals were calculated overall and by demographic characteristics. RESULTS: The reported prevalence of roads, sidewalks, paths, or trails for walking increased overall (85.3% in 2015 to 88.0% in 2020) and for many subgroups. Perceived places to walk to for relaxation, to clear your mind, and to reduce stress increased overall (72.1% in 2015 to 77.1% in 2020) and for all subgroups. Perceptions of crime as a barrier to walking decreased overall (12.5% in 2015 to 11.2% in 2020) and for some subgroups. From 2015 to 2020, the proportion of adults perceiving roads, sidewalks, paths, or trails; places to relax; and crime as a barrier to walking improved. CONCLUSIONS: Continuing to monitor perceptions of the walking environment could contribute to progress toward national walking and walkability goals in the United States.

Physical Activity Interventions During the School Day: Reviewing Policies, Practices, and Benefits.

BACKGROUND: There are many ways to increase physical activity (PA) during the school day as part of a Comprehensive School Physical Activity Plan. This article reviews policies and practices that can be used during the school day to increase PA for students. METHODS: We searched systematic reviews for articles that met criteria (2010-2018, phase 1), followed by a search for individual articles addressing topics for which we did not identify a sufficiently relevant or recent review or to update an earlier review that concluded insufficient evidence (2010-2020, phase 2). We included 45 articles (45 studies, 54 interventions). RESULTS: We grouped studies by intervention type: school-wide PA approaches to reach all students within the school setting (17), physical education (PE) interventions (13), and interventions related to recess (15). Few studies involved secondary schools or rural settings. Among 45 studies reporting PA behavior or fitness outcomes, 37 reported at least 1 improvement. CONCLUSIONS: PA policies, PE, and recess can help improve school health by increasing the PA levels of students.

Physical Activity-Friendly Policies and Community Design Features in the US, 2014 and 2021.

INTRODUCTION: The 2014 Community-Based Survey of Supports for Healthy Eating and Active Living documented the prevalence of US municipal policy and community design supports for physical activity. The survey was repeated in 2021. Our study examined change in the prevalence of supports from 2014 to 2021, overall and by municipality characteristic. METHODS: Municipalities were sampled independently each survey year. We calculated prevalence in 2014 and 2021 and the prevalence ratio (PR) for 15 supports covering zoning codes, park policies and budgets, design standards, Complete Streets policies, and shared use agreements. We used a Bonferroni-corrected Breslow-Day test to test for interaction by municipality characteristic. RESULTS: In 2014 (2,009 municipalities) compared with 2021 (1,882 municipalities), prevalence increased for several zoning codes: block sizes of walkable distances (PR = 1.46), minimum sidewalk width (PR = 1.19), pedestrian amenities along streets (PR = 1.15), continuous sidewalk coverage (PR = 1.14), and building orientation to pedestrian scale (PR = 1.08). Prevalence also increased for design standards requiring dedicated bicycle infrastructure for roadway expansion projects or street retrofits (PR = 1.19). Prevalence declined for shared use agreements (PR = 0.87). The prevalence gap widened between the most and least populous municipalities for Complete Streets policies (from a gap of 33.6 percentage points [PP] in 2014 to 54.0 PP in 2021) and for zoning codes requiring block sizes that were walkable distances (from 11.8 PP to 41.4 PP). CONCLUSION: To continue progress, more communities could consider adopting physical activity-friendly policies and design features.

Genome wide association analysis of cuticle deposition in laying hens.

The cuticle is an invisible barrier that protects the internal egg contents from microorganisms entering through gas exchange pores. Eggs which have a good cuticle are least likely to be penetrated by microorganisms and improved cuticle cover should reduce vertical transmission of microorganisms and improve biosecurity. The aim was to carry out a genome wide association study for cuticle deposition in 3 independent populations of laying hens using tartrazine and lissamine green staining. Eggs from ∼8,000 hens represented 2 White Leghorn and 1 Rhode Island Red breed. Estimates of heritability using pedigree or genomic relationship matrices were in the 0.2 to 0.3 range. The results were breed specific. Across the populations, genomic regions on chromosomes 1, 2, 4, 5, and 8 were identified as significantly associated with cuticle deposition. No single loci had a large effect. A comparison was made with genes differentially expressed in the shell gland when cuticle deposition was manipulated, however none were obvious candidates for cuticle deposition. The results support the polygenic nature of the trait and the information will help in the future to understand the genetic variance and what might control cuticle deposition and the microbiological safety of the egg.

Discovery of novel MHC-B haplotypes in Chantecler chickens.

The major histocompatibility complex (MHC) is a highly polymorphic cluster of genes which contribute to immune response. Located on chromosome 16, the chicken MHC has great influence over disease resistance and susceptibility. Through the use of a high-density SNP panel which encompasses the MHC-B region, haplotypes can be easily identified. This study aims to use an MHC-B SNP panel to evaluate the MHC-B variability in the Chantecler breed. This breed is native to Quebec, Canada, and is a dual-purpose breed known for its strong resistance to extreme cold temperatures. The Chantecler breed faced a near extinction event in the 1970s, which most likely resulted in a genetic bottleneck and loss of diversity. Despite this, SNP haplotype diversity was observed among 4 Chantecler populations. A total of 8 haplotypes were observed. Of these haplotypes, 6 were previously defined in other breeds, and the other 2 were unique to the Chantecler. Within the populations, the number of haplotypes ranged from 4 to 7, with 3 haplotypes, including the novel BSNP-Chant01, being present in all the groups. This study shows existence of reasonable diversity in the MHC-B region of the Chantecler breed and our results further contribute to understanding the variability of this region in chickens.

Major Histocompatibility Complex-B haplotype and ovarian graft response.

Gonadal tissue transfer is considered one of the best methods to preserve genetic variability. Poultry hosts can receive a gonad from a donor of a different genetic background, sustain the growth of this graft, and produce gametes from it. Unfortunately, the host's strong immune response may significantly reduce the gonadal graft's ability to reach maturity. Our study aimed to evaluate the influence of MHC-B alleles in rejecting a gonadal graft of similar or different genetic backgrounds. In the first experiment, ovarian tissue was transplanted to chicks of similar genetic backgrounds, either Lohmann White (LW) with variable MHC-B or Barred Rock (BR) with fixed MHC-B. The sustained growth of donor ovarian tissues occurred in (4/7 hosts) BR (MHC-B matched) hosts only-one of these graft-positive-BR hens produced eggs derived from the donor ovary. No grafts were recovered when the host and the donor had an LW background (0/9; MHC-B mismatched). In the second experiment, ovarian transplantation was done between chicks of either similar or different genetic backgrounds (Brown Leghorn [BL], BR, and BL/BR F1). The 2 pure lines contained only one MHC-B allele, whereas the F1 heterozygotes had both. All host birds were given a daily dose of an immunosuppressant (mycophenolate mofetil) until maturity. The success rate was assessed by microsatellite genotype confirmation of donor-derived ovaries plus physiological and histological analyses of ovarian grafts. In this second experiment, 11 out of 43 ovarian hosts laid eggs. However, all fertilized eggs from these hens were derived from the remnant host ovarian tissue, not from the donor ovaries. A necropsy assessment was done on all 43 host birds. Ten donor grafts were recovered from hosts having matched (6 hosts) and mismatched (4 hosts) MHC-B, and none were functional. Interestingly, 6 of them were enclosed by a serous membrane capsule filled with fluid and had various tissue growth. In addition, clusters of immune cells were observed in all recovered donor grafts. Our results demonstrated that genetic background could greatly influence the success of gonadal transfer in chickens.

Awareness and Knowledge of the Physical Activity Guidelines for Americans, 2nd Edition.

BACKGROUND: Assessing awareness and knowledge of the Physical Activity Guidelines for Americans, 2nd edition (Guidelines), released in 2018, is important for monitoring factors that contribute to increasing physical activity. METHODS: We estimated prevalence of awareness and knowledge of the adult aerobic guideline (≥150 min/wk of moderate-intensity equivalent aerobic physical activity preferably spread out over a week) among adults (n = 3471) and of the youth aerobic guideline (≥60 min/d of mostly moderate- to vigorous-intensity aerobic physical activity) among a subset of parents (n = 744) from a nationwide sample of US adults in the 2019 FallStyles survey. We estimated odds ratios using logistic regression, adjusting for demographic and other characteristics. RESULTS: Approximately 1 in 10 US adults and parents reported being aware of the Guidelines. Only 3% of adults knew the correct adult aerobic guideline. The most common responses were "don't know/not sure" (44%) and "30 minutes a day, 5 or more days a week" (28%). Among parents, 15% knew the youth aerobic guideline. Awareness and knowledge tended to be lower with lower education and income. CONCLUSIONS: Limited awareness and knowledge of the Guidelines suggest communication about the Guidelines could be strengthened, especially among adults with low income or education.

CD99 and the Chicken Alloantigen D Blood System.

The chicken D blood system is one of 13 alloantigen systems found on chicken red blood cells. Classical recombinant studies located the D blood system on chicken chromosome 1, but the candidate gene was unknown. Multiple resources were utilized to identify the chicken D system candidate gene, including genome sequence information from both research and elite egg production lines for which D system alloantigen alleles were reported, and DNA from both pedigree and non-pedigree samples with known D alleles. Genome-wide association analyses using a 600 K or a 54 K SNP chip plus DNA from independent samples identified a strong peak on chicken chromosome 1 at 125-131 Mb (GRCg6a). Cell surface expression and the presence of exonic non-synonymous SNP were used to identify the candidate gene. The chicken CD99 gene showed the co-segregation of SNP-defined haplotypes and serologically defined D blood system alleles. The CD99 protein mediates multiple cellular processes including leukocyte migration, T-cell adhesion, and transmembrane protein transport, affecting peripheral immune responses. The corresponding human gene is found syntenic to the pseudoautosomal region 1 of human X and Y chromosomes. Phylogenetic analyses show that CD99 has a paralog, XG, that arose by duplication in the last common ancestor of the amniotes.

Prospective Association of Daily Steps With Cardiovascular Disease: A Harmonized Meta-Analysis.

BACKGROUND: Taking fewer than the widely promoted "10 000 steps per day" has recently been associated with lower risk of all-cause mortality. The relationship of steps and cardiovascular disease (CVD) risk remains poorly described. A meta-analysis examining the dose-response relationship between steps per day and CVD can help inform clinical and public health guidelines. METHODS: Eight prospective studies (20 152 adults [ie, ≥18 years of age]) were included with device-measured steps and participants followed for CVD events. Studies quantified steps per day and CVD events were defined as fatal and nonfatal coronary heart disease, stroke, and heart failure. Cox proportional hazards regression analyses were completed using study-specific quartiles and hazard ratios (HR) and 95% CI were meta-analyzed with inverse-variance-weighted random effects models. RESULTS: The mean age of participants was 63.2±12.4 years and 52% were women. The mean follow-up was 6.2 years (123 209 person-years), with a total of 1523 CVD events (12.4 per 1000 participant-years) reported. There was a significant difference in the association of steps per day and CVD between older (ie, ≥60 years of age) and younger adults (ie, <60 years of age). For older adults, the HR for quartile 2 was 0.80 (95% CI, 0.69 to 0.93), 0.62 for quartile 3 (95% CI, 0.52 to 0.74), and 0.51 for quartile 4 (95% CI, 0.41 to 0.63) compared with the lowest quartile. For younger adults, the HR for quartile 2 was 0.79 (95% CI, 0.46 to 1.35), 0.90 for quartile 3 (95% CI, 0.64 to 1.25), and 0.95 for quartile 4 (95% CI, 0.61 to 1.48) compared with the lowest quartile. Restricted cubic splines demonstrated a nonlinear association whereby more steps were associated with decreased risk of CVD among older adults. CONCLUSIONS: For older adults, taking more daily steps was associated with a progressively decreased risk of CVD. Monitoring and promoting steps per day is a simple metric for clinician-patient communication and population health to reduce the risk of CVD.

Changes in physical activity and sedentary time in United States adults in response to COVID-19.

Physical activity is associated lower risk for a broad range of non-communicable diseases and early mortality, and even small changes in daily activity levels could have a profound effect on public health at the population level. The COVID-19 pandemic reshaped daily life for United States (US) adults resulting in reductions in physical activity early in the pandemic, but its longer-term effects on daily activities are unknown. To examine the longer-term impact of the pandemic on daily activity levels, we conducted a nationwide longitudinal study of 1,635 adults (20-75 years) in AmeriSpeak. Previous-day recalls of time-use, sedentary time, and physical activity were completed on randomly selected days in Fall 2019 (pre-pandemic) and Fall 2020. Overall, US adults reported less time in transportation (-0.47 hrs/d), more total discretionary time (0.40 hrs/d), but no changes in total sedentary time (0.10 hrs/d) or leisure-time physical activity (-0.06 hrs/d). Women reported significantly less total activity (-0.36 hrs/d) and participants with children < 13 yrs reported more sedentary time (0.60 to 0.82 hrs/d) and less moderate-to-vigorous intensity activity (-0.84 to -0.72 hrs/d). Adults without children reported no changes in sedentary time (0.02 hrs/d) or moderate-vigorous intensity activity (-0.06 hrs/d). Adults who started working from home reported no changes in physical activity, but they were among the most sedentary and least active population groups at both timepoints. Our findings describe the complex inter-play between competing behaviors as time-use demands have changed in response to the pandemic, particularly for adults with younger children. Many US adults are likely to continue working from home; therefore, implementation of evidence-based approaches to increase physical activity and reduce sedentary time in this growing population subgroup appears warranted.

The Chicken A and E Blood Systems Arise from Genetic Variation in and around the Regulators of Complement Activation Region.

The tightly linked A and E blood alloantigen systems are 2 of 13 blood systems identified in chickens. Reported herein are studies showing that the genes encoding A and E alloantigens map within or near to the chicken regulator of complement activation (RCA) gene cluster, a region syntenic with the human RCA. Genome-wide association studies, sequence analysis, and sequence-derived single-nucleotide polymorphism information for known A and/or E system alleles show that the most likely candidate gene for the A blood system is C4BPM gene (complement component 4 binding protein, membrane). Cosegregation of single-nucleotide polymorphism-defined C4BPM haplotypes and blood system A alleles defined by alloantisera provide a link between chicken blood system A and C4BPM. The best match for the E blood system is the avian equivalent of FCAMR (Fc fragment of IgA and IgM receptor). C4BPM is located within the chicken RCA on chicken microchromosome 26 and is separated from FCAMR by 89 kbp. The genetic variation observed at C4BPM and FCAMR could affect the chicken complement system and differentially guide immune responses to infectious diseases.

Daily steps and all-cause mortality: a meta-analysis of 15 international cohorts.

BACKGROUND: Although 10 000 steps per day is widely promoted to have health benefits, there is little evidence to support this recommendation. We aimed to determine the association between number of steps per day and stepping rate with all-cause mortality. METHODS: In this meta-analysis, we identified studies investigating the effect of daily step count on all-cause mortality in adults (aged ≥18 years), via a previously published systematic review and expert knowledge of the field. We asked participating study investigators to process their participant-level data following a standardised protocol. The primary outcome was all-cause mortality collected from death certificates and country registries. We analysed the dose-response association of steps per day and stepping rate with all-cause mortality. We did Cox proportional hazards regression analyses using study-specific quartiles of steps per day and calculated hazard ratios (HRs) with inverse-variance weighted random effects models. FINDINGS: We identified 15 studies, of which seven were published and eight were unpublished, with study start dates between 1999 and 2018. The total sample included 47 471 adults, among whom there were 3013 deaths (10·1 per 1000 participant-years) over a median follow-up of 7·1 years ([IQR 4·3-9·9]; total sum of follow-up across studies was 297 837 person-years). Quartile median steps per day were 3553 for quartile 1, 5801 for quartile 2, 7842 for quartile 3, and 10 901 for quartile 4. Compared with the lowest quartile, the adjusted HR for all-cause mortality was 0·60 (95% CI 0·51-0·71) for quartile 2, 0·55 (0·49-0·62) for quartile 3, and 0·47 (0·39-0·57) for quartile 4. Restricted cubic splines showed progressively decreasing risk of mortality among adults aged 60 years and older with increasing number of steps per day until 6000-8000 steps per day and among adults younger than 60 years until 8000-10 000 steps per day. Adjusting for number of steps per day, comparing quartile 1 with quartile 4, the association between higher stepping rates and mortality was attenuated but remained significant for a peak of 30 min (HR 0·67 [95% CI 0·56-0·83]) and a peak of 60 min (0·67 [0·50-0·90]), but not significant for time (min per day) spent walking at 40 steps per min or faster (1·12 [0·96-1·32]) and 100 steps per min or faster (0·86 [0·58-1·28]). INTERPRETATION: Taking more steps per day was associated with a progressively lower risk of all-cause mortality, up to a level that varied by age. The findings from this meta-analysis can be used to inform step guidelines for public health promotion of physical activity. FUNDING: US Centers for Disease Control and Prevention.

Public Health Representation on Active Transportation Bodies Across US Municipalities.

CONTEXT: Municipal bodies such as planning or zoning commissions and active transportation advisory committees can influence decisions made by local governments that support physical activity through active transportation. Public health professionals are encouraged to participate in and inform these processes. However, the extent of such collaboration among US municipalities is currently unknown. OBJECTIVE: To estimate the prevalence of active transportation bodies among US municipalities and the proportion with a designated public health representative. DESIGN: A cross-sectional survey administered from May through September 2014. SETTING: Nationally representative sample of US municipalities with populations of 1000 or more people. PARTICIPANTS: Respondents were the city or town manager, planner, or person with similar responsibilities (N = 2018). MAIN OUTCOME MEASURES: The prevalence of planning or zoning commissions and active transportation advisory committees among municipalities and whether there was a designated public health representative on them. RESULTS: Approximately 90.9% of US municipalities have a planning or zoning commission, whereas only 6.5% of these commissions have a designated public health representative. In contrast, while 16.5% of US municipalities have an active transportation advisory committee, 22.4% of them have a designated public health representative. These active transportation bodies are less common among municipalities that are smaller, rural, located in the South, and where population educational attainment is lower. Overall, few US municipalities have a planning or zoning commission (5.9%) or an active transportation advisory committee (3.7%) that also has a designated public health representative. CONCLUSIONS: Approximately 9 in 10 US municipalities have a planning or zoning commission, whereas only 1 in 6 has an active transportation advisory committee. Public health representation on active transportation bodies across US municipalities is low. Increasing the adoption of active transportation advisory committees and ensuring a designated public health representative on active transportation bodies may help promote the development of activity-friendly communities across the United States.

Surveillance of Meeting the Youth Physical Activity Guideline: Impact of Including Vigorous-Intensity and Bone-Strengthening Activities.

Purpose: The US youth physical activity guideline recommends participation in four types of physical activity: moderate-to-vigorous intensity aerobic (MVPA), vigorous-intensity aerobic (VPA), muscle-strengthening, and bone-strengthening physical activity. Current national prevalence estimates of meeting the youth physical activity guideline are typically based on measures of the MVPA and muscle-strengthening components. This study sought to examine differences in prevalence estimates using this current approach and then including measures of all four components. Methods: Data from US high school student respondents to the 2010 National Youth Physical Activity and Nutrition Survey were analyzed (n = 10,596). Prevalence of students meeting the youth physical activity guideline were assessed and compared using 1) measures of MVPA and muscle-strengthening components only and 2) also including measures of the VPA and bone-strengthening components. Results: Overall, 15.2% students met the MVPA, 50.7% met the muscle-strengthening, 70.6% met the VPA, and 80.7% met the bone-strengthening components. In total, 12.1% (95% confidence interval: 10.9, 13.3) of students met both the MVPA and muscle-strengthening components, and 11.2% (95% confidence interval: 10.0, 12.4) met all four components. Conclusions: Incorporating additional measures of VPA and bone-strengthening activity into current surveillance systems may not meaningfully impact national estimates of meeting the youth physical activity guideline.

Sex Differences in Response to Marek's Disease: Mapping Quantitative Trait Loci Regions (QTLRs) to the Z Chromosome.

Marek's Disease (MD) has a significant impact on both the global poultry economy and animal welfare. The disease pathology can include neurological damage and tumour formation. Sexual dimorphism in immunity and known higher susceptibility of females to MD makes the chicken Z chromosome (GGZ) a particularly attractive target to study the chicken MD response. Previously, we used a Hy-Line F6 population from a full-sib advanced intercross line to map MD QTL regions (QTLRs) on all chicken autosomes. Here, we mapped MD QTLRs on GGZ in the previously utilized F6 population with individual genotypes and phenotypes, and in eight elite commercial egg production lines with daughter-tested sires and selective DNA pooling (SDP). Four MD QTLRs were found from each analysis. Some of these QTLRs overlap regions from previous reports. All QTLRs were tested by individuals from the same eight lines used in the SDP and genotyped with markers located within and around the QTLRs. All QTLRs were confirmed. The results exemplify the complexity of MD resistance in chickens and the complex distribution of p-values and Linkage Disequilibrium (LD) pattern and their effect on localization of the causative elements. Considering the fragments and interdigitated LD blocks while using LD to aid localization of causative elements, one must look beyond the non-significant markers, for possible distant markers and blocks in high LD with the significant block. The QTLRs found here may explain at least part of the gender differences in MD tolerance, and provide targets for mitigating the effects of MD.