White Leghorn Chickens Research Articles

Combining supervised machine learning with statistics reveals differential gene expression patterns related to energy metabolism in the jejuna of chickens divergently selected for antibody response to sheep red blood cells

Since the 1970s, 2 lines of White Leghorn chickens, HAS and LAS, have been continuously divergently selected for 5-day postinjection antibody titer to injection with sheep red blood cells (SRBC). Antibody response is a complex genetic trait and characterizing differences in gene expression could facilitate better understanding of physiological changes due to selection and antigen exposure. At 41 d of age, randomly selected HAS and LAS chickens, which had been coraised from hatch, were either injected with SRBC (HASI and LASI) or kept as the noninjected cohort (HASN and LASN). Five days later, all were euthanized, and samples collected from the jejunum for RNA isolation and sequencing. Resulting gene expression data were analyzed combining traditional statistics with machine learning to obtain signature gene lists for functional analysis. Differences in ATP production and cellular processes were observed in the jejunum between lines and following SRBC injection. HASN vs. LASN exhibited upregulation of ATP production, immune cell motility, and inflammation. LASI exhibits upregulation of ATP production and protein synthesis vs. LASN, reflective of what was observed in HASN vs. LASN. In contrast, no corresponding upregulation of ATP production was observed in HASI vs. HASN, and most other cellular processes appear inhibited. Without exposure to SRBC, gene expression in the jejunum indicates HAS generates more ATP than LAS, suggesting HAS maintains a "primed" system; and gene expression of HASI vs. HASN further suggests this basal ATP production is sufficient for robust antibody responses. Conversely, LASI vs. LASN jejunal gene expression implies a physiological need for increased ATP production with only minimal correlating antibody production. The results of this experiment provide insight into energetic resource needs and allocations in the jejunum in response to genetic selection and antigen exposure in HAS and LAS which may help explain phenotypic differences observed in antibody response.

Areca nut and smokeless tobacco exposure induces micronucleus, other nuclear abnormalities and cytotoxicity in early chick embryo.

Areca nut (AN) and smokeless tobacco (SLT) are indiscriminately consumed among the populations of Southeast and South Asian countries, even by women during the gestational period. This study aimed to investigate the genotoxic and cytotoxic potentials of AN and Sadagura (SG), a unique homemade SLT preparation, alone and in combination in early chick embryos. Fertile white leghorn chicken eggs were randomly divided into five treatment groups: vehicle control, positive control (Mitomycin C, 20 μg/egg), AN, SG, and AN+SG. AN, SG, and AN+SG were given at dosages of 0.125, 0.25, and 0.5 mg/egg. The hen's egg test for micronucleus induction (HET-MN) was performed in chick embryos to evaluate the genotoxic potential of the test agents. Furthermore, the cytotoxic potential was assessed by studying erythroblast cell populations and the polychromatic erythrocytes (PCEs) to normochromatic erythrocytes (NCEs) ratio. Our results indicated a significant increase (p < .001) in MN frequency and other nuclear abnormalities, suggesting the potential of AN and SG to cause genotoxicity. Also, AN and SG exposure alone and in combination considerably altered the erythroblast cell population (%) and the PCE to NCE ratio in all the treatment periods. Our findings established the genotoxic and cytotoxic potential of both AN and SG alone and in combination during early embryonic development in the chick embryo.

Identification of single nucleotide polymorphisms in GnRH-I, GnRH-II/MRPS26, GnRHR exons and their Association with egg production in Anand Synthetic White Leghorn and Anand Bantamised White Leghorn Chicken

The aim of study was to identify Single Nucleotide Polymorphisms (SNPs) in the exon regions of GnRH-I, GnRH-II/MRPS26 and GnRHR genes and to assess their association with egg production up to 64 weeks of age (EN64) in chicken. Blood samples were collected from 48 Anand Synthetic White Leghorn (ASWLH) and 48 Anand Bantamised White Leghorn (ABWLH) chicken. Custom panel was designed for these genes’ exon regions and amplicon sequencing was performed on Illumina Miseq platform. Total 41 SNPs (19 previously reported and 22 novel SNPs) were identified from 96 samples. Association analysis revealed that rs314996211 (p&lt;0.05), rs313100310 (p&lt;0.01), g.17308550T&gt;C (p&lt;0.01) of GnRHR were significantly associated with EN64. Conclusively, rs314996211, rs313100310, g.17308550T&gt;C of GnRHR can be implemented as selection markers associated with EN64 in chicken.

The production of Newcastle disease virus-like particles in Nicotiana benthamiana as potential vaccines.

Newcastle disease (ND) is a highly contagious viral respiratory and neurological disease that has a severe impact on poultry production worldwide. In the present study, an expression platform was established for the transient production in N.bethamiana of ND virus-like particles (VLPs) for use as vaccines against ND. The expression of the ND Fusion (F) and/or Hemagglutinin-neuraminidase (HN) proteins of a genotype VII.2 strain formed ND VLPs in planta as visualized under the transmission electron microscope, and HN-containing VLPs agglutinated chicken erythrocytes with hemagglutination (HA) titres of up to 13 log2.The immunogenicity of the partially-purified ND VLPs was confirmed in specific-pathogen-free White leghorn chickens. Birds receiving a single intramuscular immunization with 1024 HA units (10 log2) of the F/HN ND VLPs administered with 20% [v/v] Emulsigen®-P adjuvant, seroconverted after 14 days with F- and HN-specific antibodies at ELISA titres of 5705.17 and HI geometric mean titres (GMTs) of 6.2 log2, respectively. Furthermore, these ND-specific antibodies successfully inhibited viral replication in vitro of two antigenically closely-related ND virus isolates, with virus-neutralization test GMTs of 3.47 and 3.4, respectively. Plant-produced ND VLPs have great potential as antigen-matched vaccines for poultry and other avian species that are highly immunogenic, cost-effective, and facilitate prompt updating to ensure improved protection against emerging ND field viruses.

Expression profiling of IL-1β, IL-6 and IL-8 genes in lung tissues of Aseel, Crossbred Naked neck, and White Leghorn chicken challenged with H9N2 Influenza virus

Aseel and Naked neck are major chicken breeds of the tropics and well-known for their thermotolerance and robustness. However, both of them especially Aseel are very susceptible to Avian Influenza (AI) which cause huge mortalities. The role of cytokines in relation to the pathology and severity of the disease caused by the endemic strain (H9N2) of AIV in these breeds remained thus far unclear. The aim of this study was to investigate the effects of H9N2 AIV on the expression level of IL-1β, IL-6 and IL-8 in the lung tissues of Aseel, crossbred Naked Neck, and White Leghorn (WLH). In total 60 birds, 20 from each breed, were used in this study, whereas 30 birds (10 from each breed) were challenged intranasally with H9N2 virus with a concentration of 106 EID50 at 6wk of age and other half were treated as control. The lung tissues were sampled at 5th day post-infection to study the differential expression of IL-1β, IL-6, and IL-8 using qRT-PCR. Our data revealed a significant difference (P&lt;0.001) in the gene expression levels among all the breeds in response to viral challenge. It was also observed that after exposure to H9N2 virus, Aseel birds showed the highest increase in their expressions of interleukin (IL-1 β, IL-6, and IL-8) genes followed by Naked Neck and WLH respectively suggesting greater susceptibility of Aseel to AIV compared with other breeds. However, these results are in agreement with the severity of disease and incidence of mortality caused by AI in these breeds.

Evaluation of growth performance and feed efficiency in reciprocal crosses of Fayoumi with three exotic chicken breeds

ABSTRACT Reciprocal crosses of Fayoumi with Koekoek, Sasso, and White Leghorn chickens and the purebreds were evaluated for growth and feed efficiency traits. Birds were weighed individually at hatch and every four weeks to 20 weeks, and body weight gain was the difference between consecutive records. Feed conversion ratio was the ratio of feed consumed to weight gained by the birds. Results revealed significant differences among the genotypes in those traits. Sasso outperformed all other genotypes throughout the study period. Reciprocal crosses of Fayoumi and Sasso performed better than the remaining seven genotypes, with Koekoek and reciprocals of Fayoumi and Koekoek showing intermediate performance, but Fayoumi and White Leghorn and reciprocals involving them performed the least. In most instances, reciprocals of Fayoumi with Koekoek and White Leghorn outperformed both of their parents. Therefore, these genotypes could be used in any crossbreeding system to exploit the heterotic effects that existed in them.

Are the two polymorphic sites of anti-Marek’s disease in White Leghorn chickens also suitable for Partridge Shank chickens?

<b>Background: </b>The selection of Marek’s disease (MD)-resistant breeds in Partridge Shank chicken, a popular local chicken breed in Henan Province of China, has practical value. We hypothesized that the two polymorphic sites (<i>rs14527240</i> located in <i>SMOC1</i> and <i>GGaluGA156129</i> located in PTPN3) related to MD resistance in White Leghorn chickens are also applicable to Partridge Shank chickens. <b>Methods: </b>In this experiment, we screened 10 live hens and 2 live roosters with the double GG genotype by genotyping the two sites from 6500 Partridge Shank chickens. Nineteen one-day-old chicks with the double GG genotype were obtained by artificial insemination. Seventy-two one-day-old chickens (19 from the population expansion test and 53 randomly selected from chicken farms) were injected with 2000 plaque-forming units of the Md5 virus strain. After 100 days of infection, all chickens were examined by pathological anatomical examination, histological sectioning, genotyping, and a quantitative polymerase chain reaction of <i>SMOC1</i> and <i>PTPN3</i>. <b>Results:</b> There was only one site (<i>rs14527240</i> located in <i>SMOC1</i>) associated with MD in Partridge Shank chickens (<i>p</i> < 0.05), but the GG genotype of <i>SMOC1</i> in Partridge Shank chickens indicated susceptibility to MD. <i>SMOC1</i> expression in MD-susceptible chickens was also significantly higher than that in MDresistant chickens (<i>p</i> < 0.05). <b>Conclusion: </b>Therefore, the MD resistance sites selected from White Leghorn chickens were not completely suitable for Partridge Shank chickens, but they can be used as a reference. This study indicated that <i>SMOC1</i> plays an important role in screening for MD resistance in poultry.

Evaluation of immunogenicity and efficacy of the enterobactin conjugate vaccine in protecting chickens from colibacillosis.

Colibacillosis is one of the most common and economically devastating infectious diseases in poultry production worldwide. Innovative universal vaccines are urgently needed to protect chickens from the infections caused by genetically diverse avian pathogenic Escherichia coli (APEC). Enterobactin (Ent) is a highly conserved siderophore required for E. coli iron acquisition and pathogenesis. The Ent-specific antibodies induced by a novel Ent conjugate vaccine significantly inhibited the in vitro growth of diverse APEC strains. In this study, White Leghorn chickens were immunized with the Ent conjugate vaccine using a crossed design with two variables, vaccination (with or without) and APEC challenge (O1, O78, or PBS control), resulting in six study groups (9 to 10 birds/group). The chickens were subcutaneously injected with the vaccine (100μg per bird) at 7days of age, followed by booster immunization at 21days of age. The chickens were intratracheally challenged with an APEC strain (108 CFU/bird) or PBS at 28days of age. At 5days post infection, all chickens were euthanized to examine lesions and APEC colonization of the major organs. Immunization of chickens with the Ent vaccine elicited a strong immune response with a 64-fold increase in the level of Ent-specific IgY in serum. The hypervirulent strain O78 caused extensive lesions in lung, air sac, heart, liver, and spleen with significantly reduced lesion scores observed in the vaccinated chickens. Interestingly, the vaccination did not significantly reduce APEC levels in the examined organs. The APEC O1 with low virulence only caused sporadic lesions in the organs in both vaccination and control groups. The Ent conjugate vaccine altered the bacterial community of the ileum and cecum. Taken together, the findings from this study showed the Ent conjugate vaccine could trigger a strong specific immune response and was promising to confer protection against APEC infection.

Outer membrane protein BamA-based ELISA differentiates Salmonella-vaccinated chickens from naturally infected chickens.

Salmonella often causes subclinical infection in chickens, but antibody tests can find infected individuals and control the spread of infection. In this study, the S. Typhimurium-specific outer membrane, β-barrel assembly machinery protein A (BamA), was overexpressed in Escherichia coli and purified as a coating antigen to develop a BamA-based enzyme-linked immuno sorbent assay for detecting Salmonella infection. The presence of anti-BamA IgG was detected in the sera of infected BALB/c mice, but not in that of heat-killed Salmonella-vaccinated mice. The assay was validated using White Leghorn chickens and showed similar results. The detection of BamA antibodies in the sera can differentiate infected chickens from vaccinated chickens. This assay will be useful for monitoring Salmonella infection in chickens and possibly in other animals.

Non-viral vaccination through cationic guanidium polymer-pDNA polyplex mediated gene transfer.

Vaccination through cellular transfection of nucleotide-based vaccines is a powerful approach to combatting disease. Plasmid DNA (pDNA) vaccines are particularly promising vectors for non-viral immunomodulation that afford high degrees of potency and flexibility. Versatile guanidinium-functionalized poly(oxanorbornene)imide (PONI-Guan) homopolymers were used to facilitate non-disruptive pDNA condensation into discrete polyplexes, enabling efficient in vitro transfection of endothelial cells and HD-11 macrophages. Translation of these vectors for vaccination of white leghorn chickens against Newcastle disease virus (NDV) elicited strong humoral immune responses against the virus. This approach presents a highly versatile method for targeted immunomodulation in vivo, with the potential for translatability as a non-viral vaccine platform.

Molecular analysis of chicken interferon-alpha inducible protein 6 gene and transcriptional regulation.

Interferon-alpha inducible protein 6 (IFI6) is an interferon-stimulated gene (ISG), belonging to the FAM14 family of proteins and is localized in the mitochondrial membrane, where it plays a role in apoptosis. Transcriptional regulation of this gene is poorly understood in the context of inflammation by intracellular nucleic acid-sensing receptors and pathological conditions caused by viral infection. In this study, chicken IFI6 (chIFI6) was identified and studied for its molecular features and transcriptional regulation in chicken cells and tissues, i.e., lungs, spleens, and tracheas from highly pathogenic avian influenza virus (HPAIV)-infected chickens. The chIFI6-coding sequences contained 1638 nucleotides encoding 107 amino acids in three exons, whereas the duck IFI6-coding sequences contained 495 nucleotides encoding 107 amino acids. IFI6 proteins from chickens, ducks, and quail contain an IF6/IF27-like superfamily domain. Expression of chIFI6 was higher in HPAIV-infected White Leghorn chicken lungs, spleens, and tracheas than in mock-infected controls. TLR3 signals regulate the transcription of chIFI6 in chicken DF-1 cells via the NF-κB and JNK signaling pathways, indicating that multiple signaling pathways differentially contribute to the transcription of chIFI6. Further research is needed to unravel the molecular mechanisms underlying IFI6 transcription, as well as the involvement of chIFI6 in the pathogenesis of HPAIV in chickens.

Transcriptomic analysis reveals the dynamic changes of transcription factors during early development of chicken embryo

BackgroundThe transition from fertilized egg to embryo in chicken requires activation of hundreds of genes that were mostly inactivated before fertilization, which is accompanied with various biological processes. Undoubtedly, transcription factors (TFs) play important roles in regulating the changes in gene expression pattern observed at early development. However, the contribution of TFs during early embryo development of chicken still remains largely unknown that need to be investigated. Therefore, an understanding of the development of vertebrates would be greatly facilitated by study of the dynamic changes in transcription factors during early chicken embryo.ResultsIn the current study, we selected five early developmental stages in White Leghorn chicken, gallus gallus, for transcriptome analysis, cover 17,478 genes with about 807 million clean reads of RNA-sequencing. We have compared global gene expression patterns of consecutive stages and noted the differences. Comparative analysis of differentially expressed TFs (FDR < 0.05) profiles between neighboring developmental timepoints revealed significantly enriched biological categories associated with differentiation, development and morphogenesis. We also found that Zf-C2H2, Homeobox and bHLH were three dominant transcription factor families that appeared in early embryogenesis. More importantly, a TFs co-expression network was constructed and 16 critical TFs were identified.ConclusionOur findings provide a comprehensive regulatory framework of TFs in chicken early embryo, revealing new insights into alterations of chicken embryonic TF expression and broadening better understanding of TF function in chicken embryogenesis.

Experimental infection of aquatic bird bornavirus 1 in domestic chickens

Aquatic bird bornavirus 1 (ABBV-1), classified in the Orthobornavirus genus, is a neurotropic virus that infects wild waterfowl causing persistent infection of the nervous system. Given the conspicuous presence of wild waterfowl in urban areas and farmlands, spillover of this virus into domesticated poultry species is a concern. The goal of this study was to test the ability of ABBV-1 to infect and cause disease in chickens. Two day-old, White Leghorn chickens (n, 176) were inoculated with ABBV-1 through the oral, intramuscular, or intracranial routes, and sampled at 1, 4, 8, and 12-weeks post infection (wpi) to assess virus replication and lesion development. Chickens became infected only through the intracranial and intramuscular routes, developing earliest infection in the brain by 1 wpi (intracranial group), and spinal cord by 8 wpi (intramuscular group). Except for the kidney of one bird in the intracranial group, no other tissues (including choanal and cloacal swabs) tested positive for the virus. Therefore, while the virus could reach the central nervous tissue (CNS) from the muscle in approximately 20% of birds (centripetal spread), it inefficiently reached peripheral sites after replication in the CNS (centrifugal spread). Inflammation in the CNS was observed in the intracranial and intramuscular groups starting at 8 and 12 wpi, respectively, and consisted of mononuclear perivascular cuffing. This is the first study to document the susceptibility of chickens to ABBV-1 infection, and indicates that this species can become infected with ABBV-1, although less extensively than what is observed in waterfowl. This suggests that ABBV-1 replication is partially restricted in gallinaceous birds.

Validation of SNPs Identified by Amplicon Sequencing and their Association with Egg Production and Egg Weight in Anand Synthetic White Leghorn and Anand Bantamised White Leghorn Chicken

The present study was aimed to validate the previously found SNPs using NGS-based amplicon sequencing and investigate of their association with egg production and egg weight by PCR-RFLP in Anand Synthetic White Leghorn (ASWLH) and Anand Bantamised White Leghorn (ABWLH) chicken. A total of 500 blood samples were collected including, 227 samples of ASWLH and 273 of ABWLH maintained at the Poultry Research Station, Anand Agricultural University, Anand, Gujarat. The study was conducted for a total of eight SNP markers located across the four genes involved in physiological pathways related to egg production and egg weight, viz., GnRHII (T88170424C), GnRHII (G88170427A), VIPR1 (C1826542A), VIPR1 (C1826555T), OCX32 (C21912308T), OCX32 (T21912084G), OCX32 (C21912423A) and GHR (C13415980T). Out of eight SNPs, C21912423A of the OCX32 gene was significantly associated with egg weight at the 40 weeks of age (EW40) in the whole population. The G88170427A of the GnRHII gene was significantly associated with egg weight at the 28 weeks of age (EW28) and C21912308T of the OCX-32 gene was significantly associated with total egg number at the age of 64 weeks (TWN64) in the whole population.

Cecum microbiome and metabolism characteristics of Silky Fowl and White Leghorn chicken in late laying stages.

Cecal microflora plays a key role in the production performance and immune function of chickens. White Leghorn (WL) is a well-known commercial layer line chicken with high egg production rate. In contrast, Silky Fowl (SF), a Chinese native chicken variety, has a low egg production rate, but good immune performance. This study analyzed the composition of cecal microbiota, metabolism, and gene expression in intestinal tissue of these varieties and the correlations among them. Significant differences were observed in the cecal microbes: Bacteroides was significantly enriched in WL, whereas Veillonellaceae and Parabacteroides were significantly enriched in SF. Carbohydrate biosynthesis and metabolism pathways were significantly upregulated in WL cecum, which might provide more energy to the host, leading to persistently high levels of egg production. The higher Parabacteroides abundance in SF increased volicitin content, enhanced α-linolenic acid metabolism, and significantly negatively correlated with metabolites of propanoate metabolism and carbohydrate metabolism. Genes related to lipid metabolism, immunity, and melanogenesis were significantly upregulated in the SF cecum, regulating lipid metabolism, and participating in the immune response, while genes related to glucose metabolism and bile acid metabolism were expressed at higher levels in WL, benefiting energy support. This study provided a mechanism for intestinal microorganisms and metabolic pathways to regulate chicken egg-laying performance and immunity.

Prediction of transcript isoforms in 19 chicken tissues by Oxford Nanopore long-read sequencing.

To identify and annotate transcript isoforms in the chicken genome, we generated Nanopore long-read sequencing data from 68 samples that encompassed 19 diverse tissues collected from experimental adult male and female White Leghorn chickens. More than 23.8 million reads with mean read length of 790 bases and average quality of 18.2 were generated. The annotation and subsequent filtering resulted in the identification of 55,382 transcripts at 40,547 loci with mean length of 1,700 bases. We predicted 30,967 coding transcripts at 19,461 loci, and 16,495 lncRNA transcripts at 15,512 loci. Compared to existing reference annotations, we found ∼52% of annotated transcripts could be partially or fully matched while ∼47% were novel. Seventy percent of novel transcripts were potentially transcribed from lncRNA loci. Based on our annotation, we quantified transcript expression across tissues and found two brain tissues (i.e., cerebellum and cortex) expressed the highest number of transcripts and loci. Furthermore, ∼22% of the transcripts displayed tissue specificity with the reproductive tissues (i.e., testis and ovary) exhibiting the most tissue-specific transcripts. Despite our wide sampling, ∼20% of Ensembl reference loci were not detected. This suggests that deeper sequencing and additional samples that include different breeds, cell types, developmental stages, and physiological conditions, are needed to fully annotate the chicken genome. The application of Nanopore sequencing in this study demonstrates the usefulness of long-read data in discovering additional novel loci (e.g., lncRNA loci) and resolving complex transcripts (e.g., the longest transcript for the TTN locus).

Growth Performance of Kuroiler (Rhode Island x White Leghorn) Chickens Fed Aflatoxin Contaminated Maize- Based Diets Treated with Different Amounts of Lemon (Limon citrus) Juice

Aflatoxin contamination in feed and feed ingredients is prevalent worldwide, and poses serious risks to both livestock and humans. This study was conducted to assess the effects of feeding Aflatoxin (AF) contaminated maize-based diets treated with varying levels of Lemon juice, to Kuroiler chickens on their growth performance. Lemon juice was extracted from fruits purchased from the local market and mixed with isocaloric and Isonitrogenic diets (starter, grower and finisher) containing AF-contaminated maize, at 0, 250, 500 and 750ml Lemon juice/Kg of feed. The diets were left to dry for 24hrs, after which 100g samples were collected from each diet to measure and compare the residual AF levels. Then, 100 day-old Kuroiler chicks were sourced from a local hatchery, and divided into four treatment groups (n = 25). Each group was replicated four times. The treatment groups were randomly assigned to 0, 250, 500, and 750ml Lemon juice/Kg feed –treated diets. These feeds and clean drinking water, were supplied to the birds ad libitum for 49 days. Feed intake was monitored every day, and body weights, weight gains, and feed conversion ratios were assessed every week. It was observed that the amount of residual AF in each diet depended on the amount of lemon juice used to treat it. Untreated diet had the highest AF levels at 36 ppb, followed by that which was treated with 250, 500, 750 ml Lemon juice/Kg feed at 28.1, 21.3, and 7.4 ppb, respectively. Growth performance variables assessed were also influenced by the amounts of residual AF levels in the diet. Birds fed diets with the lowest residual AF levels at 7.4 ppb had the best (p &lt; 0.05) growth performance in all the variables, while the least (p &lt; 0.05) was observed in birds fed untreated diet, followed by those that were fed diets treated with 250 and 500ml Lemon juice/Kg feed. It was concluded that Lemon juice was able to degrade AF in diets that had maize contaminated with AF, but the extent to which it inactivated it, depended on the amount of juiced used. Similarly, growth performance of birds fed diets with AF-contaminated maize treated with lemon juice was also dependent on the levels of residual AF in feeds after treatment, with the best performance observed in chickens fed diets treated with 750ml Lemon juice per Kg feed.

SNPs Identification in production related genes in strains of white leghorn chicken

This is the first comprehensive study aimed to determine Single Nucleotide Polymorphisms (SNPs) in candidate genes (GHR, IGF1, OCX-32 and GDF9) reported to associated with egg production at the age of 64 weeks (EP64) in strains of White Leghorn chicken (Anand Synthetic White Leghorn and Anand Bantamised White Leghorn by sequencing the coding region of respective genes. Both the strains of White Leghorn chicken were categorized into four different groups viz., Anand Synthetic White Leghorn High Production (ASHP), Anand Synthetic White Leghorn Low Production (ASLP), Anand Bantamised White Leghorn High Production (ABHP) and Anand Bantamised White Leghorn Low Production (ABLP) to find out SNPs in coding region of candidate genes and its association with EP64. The genomic DNA was extracted for 96 chickens and then further sequenced with the designed custom amplicon panel on the Illumina MiSeq platform. Raw data collected after sequencing was used for the bio in formatic analysis to confirm its association with EP64. Consequently, over 99% target regions were amplifed and 87 SNPs were available after quality filtering. Only thirty-three variants were novel while majority of the identified variants were catalogued in dbSNP database as known variants. The T21912084G, C21912423A and rs318030570 of OCX-32 and C13415980T of GHR gene was found to have a significant association (p

MicroRNAs with non-additive expression in the ovary of hybrid hens target genes enriched in key reproductive pathways that may influence heterosis for egg laying traits.

Heterosis has been extensively exploited in chicken breeding to improve laying traits in commercial hybrid stock. However, the molecular mechanisms underlying it remains elusive. This study characterizes the miRNAome in the pre-hierarchical follicles of purebred and hybrid laying hens, and investigate the functions of miRNAs with non-additive expression in the pre-hierarchical follicles as they modulate heterosis for egg number and clutch size. To achieve that aim, White Leghorn and Rhode Island Red chicken lines were reciprocally crossed to generate hybrids. The crossbreds demonstrated heterosis for egg number and clutch size, and pre-hierarchical follicles from 4 birds of each genotype were collected at 53 weeks of age. Mode of miRNA expression was characterized after miRNA sequencing. A total of 50 miRNAs including 30 novel ones, were found to exhibit non-additive expression. Dominance was the predominant mode of expression exhibited by majority of the miRNAs. Functional analysis of target genes of the known miRNAs with non-additive expression revealed Gene Ontology terms related to regulation of transcription, metabolic processes and gene expression. KEGG and REACTOME pathways including hedgehog, cellular senescence, wnt, TGF-β, progesterone-mediated oocyte maturation, oocyte meiosis, GnRH signaling, signal transduction and generic transcription, which can be linked to primordial follicle activation, growth and ovulation, were significantly enriched by target genes of miRNAs with non-additive expression. Majority of the genes enriched in these biological pathways were targeted by gga-miR-19a, gga-miR-19b, gga-miR-375, gga-miR-135a, and gga-miR-7 and 7b, thus, revealing their synergistic roles in enhancing processes that could influence heterosis for egg number and clutch size in hybrid hens.

Research Note: Heterosis for egg production and oviposition pattern in reciprocal crossbreeds of indigenous and elite laying chickens

Heterosis has been widely utilized in chicken breeding to improve economically important traits. However, few studies focused on revealing the factors contributing to egg production heterosis. In this study, White Leghorn and Beijing-You chickens were used as parental breeds to generate purebreds (WW, YY) and reciprocal crossbreeds (WY, YW) to characterize heterosis for egg production traits including age at first egg (AFE), clutch traits, oviposition pattern, and egg quality traits. Results showed that egg number until 35 wk of age (EN35) was higher in crossbreeds than the average of purebreds (P < 0.05) and exhibited positive heterosis of 4.03% and 2.84%) in WY and YW respectively. Crossbreeds commenced laying earlier than the average of purebreds (P < 0.05) with negative heterosis of −1.24% and −0.92% for WY and YW respectively. Moreover, EN35 had negative correlation with AFE (r = −0.85) and positive correlation with average clutch length (ACL) (r = 0.48) and maximum clutch length (MCL) (r = 0.66). However, negative heterosis for ACL (−19.62%, −16.51%) and MCL (−22.88%, −18.97%) were obtained in WY and YW, respectively. This may be due to the positive heterosis for number of pauses, which was highly correlated with ACL (r = −0.68) and MCL (r = −0.74). The crossbreeding improved the oviposition pattern. Percent egg laying that occurs between 7:00 and 14:00 was 91.50% (WW), 68.28% (YY), 76.87% (WY), and 79.68% (YW) in the experimental populations. On the other hand, oviposition interval (OI) had negative heterosis in crossbreeds and was negatively correlated with EN35 (r = −0.60). Positive heterosis for egg weight of 2.63% and 3.94% and yolk weight of 4.74% and 6.07% were observed in WY and YW, respectively. Taken together, egg production related traits did not contribute equally to EN heterosis. The AFE and OI exhibited significant correlation with EN indicating that they would be important drivers for EN heterosis.