Genetic Lines Of Chickens Research Articles

Different MHC class I cell surface expression levels in diverse chicken lines, associations with B blood group, and proposed relationship to antigen-binding repertoire

The Major Histocompatibility Complex (MHC) is a cluster of genes with primarily immune-related functions. The MHC class I genes are responsible for self- versus non-self-recognition and viral antigen presentation to T lymphocytes. The chicken MHC class I protein binds its cognate antigen(s) over a repertoire spectrum ranging from promiscuous (generalist) to fastidious (specialist). The MHC class I protein expression level at the cell surface is inversely related to the promiscuity of its peptide-binding repertoire. In our study, erythrocytes from 6 diverse and highly inbred lines of chickens, a closed broiler line, and a highly advanced intercross line were evaluated for MHC class I antigen expression level by flow cytometry using monoclonal antibodies to chicken MHC class I molecules. In chickens, the B blood group antigens include the MHC class I antigen expressed from the MHC. Thus, the B blood group has historically been used as a genetic marker for Marek's Disease virus response. Erythrocytes of the inbred lines were blood typed by serology. The B21 blood type is widely recognized as relatively resistant to Marek's disease and regarded as an MHC class I generalist with low MHC class I expression. The Spanish line, which types serologically as B21.1 (similar to B21), was the lowest MHC class I expressing line. The two sublines (B5.1 and B15.2) of the Fayoumi breed, which significantly differed in their MHC class I expression, also differ in response to multiple pathogens. These defined genetic lines of chickens, with distinct MHC class I expression levels, provide an excellent platform to further interrogate the hypothesis of high or low MHC class I expression (antigenic specialists or generalists, respectively) determining diverse responses to pathogens.

Differences in caecal microbiota composition and Salmonella carriage between experimentally infected inbred lines of chickens

BackgroundSalmonella Enteritidis (SE) is one of the major causes of human foodborne intoxication resulting from consumption of contaminated poultry products. Genetic selection of animals that are more resistant to Salmonella carriage and modulation of the gut microbiota are two promising ways to decrease individual Salmonella carriage. The aims of this study were to identify the main genetic and microbial factors that control the level of Salmonella carriage in chickens (Gallus gallus) under controlled experimental conditions. Two-hundred and forty animals from the White Leghorn inbred lines N and 61 were infected by SE at 7 days of age. After infection, animals were kept in isolators to reduce recontamination of birds by Salmonella. Caecal contents were sampled at 12 days post-infection and used for DNA extraction. Microbiota DNA was used to measure individual counts of SE by digital PCR and to determine the bacterial taxonomic composition, using a 16S rRNA gene high-throughput sequencing approach.ResultsOur results confirmed that the N line is more resistant to Salmonella carriage than the 61 line, and that intra-line variability is higher for the 61 line. Furthermore, the 16S analysis showed strong significant differences in microbiota taxonomic composition between the two lines. Among the 617 operational taxonomic units (OTU) observed, more than 390 were differentially abundant between the two lines. Furthermore, within the 61 line, we found a difference in the microbiota taxonomic composition between the high and low Salmonella carriers, with 39 differentially abundant OTU. Using metagenome functional prediction based on 16S data, several metabolic pathways that are potentially associated to microbiota taxonomic differences (e.g. short chain fatty acids pathways) were identified between high and low carriers.ConclusionsOverall, our findings demonstrate that the caecal microbiota composition differs between genetic lines of chickens. This could be one of the reasons why the investigated lines differed in Salmonella carriage levels under experimental infection conditions.

Differential immunological response detected in mRNA expression profiles among diverse chicken lines in response to Salmonella challenge

Salmonella enterica serovar Enteritidis is a bacterial pathogen that contributes to poultry production losses and human foodborne illness. The bacterium elicits a broad immune response involving both the innate and adaptive components of the immune system. Coordination of the immune response is largely directed by cytokines. The objective of the current study was to characterize the expression of a select set of cytokines and regulatory immune genes in three genetically diverse chicken lines after infection with S. Enteritidis. Leghorn, Fayoumi and broiler day-old chicks were orally infected with pathogenic S. Enteritidis or culture medium. At 2 and 18 h postinfection, spleens and ceca were collected and mRNA expression levels for 7 genes (GM-CSF, IL2, IL15, TGF-β1, SOCS3, P20K, and MHC class IIβ) were evaluated by real-time quantitative PCR. Genetic line had a significant effect on mRNA expression levels of IL15, TGF-β1, SOCS3 and P20K in the spleen and on P20K and MHC class IIβ in the cecum. Comparing challenged vs. unchallenged birds, the expression of SOCS3 and P20K mRNA were significantly higher in the spleen and cecum, while MHC class IIβ mRNA was significantly lower in spleen. Combining the current RNA expression results with those of previously reported studies on the same samples reveals distinct RNA expression profiles among the three genetic chicken lines and the 2 tissues. This study illustrates that these diverse genetic lines have distinctively different immune response to S. Enteritidis challenge within the spleen and the cecum.

RNA Sequencing revealed differentially expressed genes functionally associated with immunity and tumor suppression during latent phase infection of a vv\u2009+\u2009MDV in chickens

Very virulent plus Marek’s disease (MD) virus (vv + MDV) induces tumors in relatively resistant lines of chickens and early mortality in highly susceptible lines of chickens. The vv + MDV also triggers a series of cellular responses in both types of chickens. We challenged birds sampled from a highly inbred chicken line (line 63) that is relatively resistant to MD and from another inbred line (line 72) that is highly susceptible to MD with a vv + MDV. RNA-sequencing analysis was performed with samples extracted from spleen tissues taken at 10-day and 21-day post infection (dpi). A total of 64 and 106 differentially expressed genes was identified in response to the vv + MDV challenge at latent phase in the resistant and susceptible lines of chickens, respectively. Direct comparisons between samples of the two lines identified 90 and 126 differentially expressed genes for control and MDV challenged groups, respectively. The differentially expressed gene profiles illustrated that intensive defense responses were significantly induced by vv + MDV at 10 dpi and 21 dpi but with slight changes in the resistant line. In contrast, vv + MDV induced a measurable suppression of gene expression associated with host defense at 10 dpi but followed by an apparent activation of the defense response at 21 dpi in the susceptible line of chickens. The observed difference in gene expression between the two genetic lines of chickens in response to MDV challenge during the latent phase provided a piece of indirect evidence that time points for MDV reactivation differ between the genetic lines of chickens with different levels of genetic resistance to MD. Early MDV reactivation might be necessary and potent to host defense system readiness for damage control of tumorigenesis and disease progression, which consequently results in measurable differences in phenotypic characteristics including early mortality (8 to 20 dpi) and tumor incidence between the resistant and susceptible lines of chickens. Combining differential gene expression patterns with reported GO function terms and quantitative trait loci, a total of 27 top genes was selected as highly promising candidate genes for genetic resistance to MD. These genes are functionally involved with virus process (F13A1 and HSP90AB1), immunity (ABCB1LB, RGS5, C10ORF58, OSF-2, MMP7, CXCL12, GAL1, GAL2, GAL7, HVCN1, PDE4D, IL4I1, PARP9, EOMES, MPEG1, PDK4, CCLI10, K60 and FST), and tumor suppression (ADAMTS2, LXN, ARRDC3, WNT7A, CLDN1 and HPGD). It is anticipated that these findings will facilitate advancement in the fundamental understanding on mechanisms of genetic resistance to MD. In addition, such advancement may also provide insights on tumor virus-induced tumorigenesis in general and help the research community recognize MD study may serve as a good model for oncology study involving tumor viruses.

Liver transcriptome response to hyperthermic stress in three distinct chicken lines

BackgroundHigh ambient temperatures cause stress in poultry, especially for broiler lines, which are genetically selected for rapid muscle growth. RNA-seq technology provides powerful insights into environmental response from a highly metabolic tissue, the liver. We investigated the effects of acute (3 h, 35 °C) and chronic (7d of 35 °C for 7 h/d) heat stress on the liver transcriptome of 3-week-old chicks of a heat-susceptible broiler line, a heat-resistant Fayoumi line, and their advanced intercross line (AIL).ResultsTranscriptome sequencing of 48 male chickens using Illumina HiSeq 2500 technology yielded an average of 33.9 million, 100 base-pair, single-end reads per sample. There were 8 times more differentially expressed genes (DEGs) (FDR < 0.05) in broilers (n = 627) than Fayoumis (n = 78) when comparing the acute-heat samples to the control (25 °C) samples. Contrasting genetic lines under similar heat treatments, the highest number of DEGs appeared between Fayoumi and broiler lines. Principal component analysis of gene expression and analysis of the number of DEGs suggested that the AIL had a transcriptomic response more similar to the Fayoumi than the broiler line during acute heat stress. The number of DEGs also suggested that acute heat stress had greater impact on the broiler liver transcriptome than chronic heat stress. The angiopoietin-like 4 (ANGPTL4) gene was identified as differentially expressed among all 6 contrasts. Ingenuity Pathway Analysis (IPA) created a novel network that combines the heat shock protein family with immune response genes.ConclusionsThis study extends our understanding of the liver transcriptome response to different heat exposure treatments in distinct genetic chicken lines and provides information necessary for breeding birds to be more resilient to the negative impacts of heat. The data strongly suggest ANGPTL4 as a candidate gene for improvement of heat tolerance in chickens.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-3291-0) contains supplementary material, which is available to authorized users.

The Influence of Major Histocompatibility Complex and Vaccination with Turkey Herpesvirus on Marek's Disease Virus Evolution.

Over the last five decades, the pathogenicity of the Marek's disease virus (MDV) has evolved from the relatively mild strains (mMDV) observed in the 1960s to the more severe very-virulent-plus strains currently observed in today's outbreaks. The use of vaccines to control Marek's disease (MD), but not the infection cycle, is thought to be the major influence on the evolution of MDV. Selection for genetic resistance to MD has also been employed by the industry to control MD in the commercial setting but the role of host genetics on the evolution of MDV has been difficult to investigate in the field. To investigate the influence of vaccination and host resistance we developed a laboratory model to control and assess the effects of virus and animal genetics on MDV evolution. A bacterial artificial chromosome-derived MDV (Md5B40BAC) was used for in vivo passage (IVP) through turkey herpesvirus (HVT)-vaccinated resistant (MHC-B21) and susceptible (MHC-B13) genetic chicken lines. During IVP in the vaccinated susceptible line, the disease incidence increased from 23% MD in the first IVP to 53% MD during the fifth IVP. In the vaccinated resistant line, disease incidence increased from 0% MD during the first IVP to 29% MD during the fifth IVP. Although the IVP isolates remained relatively mild in the vaccinated resistant chicken line (29% MD) they increased from 0% to 63% MD when used to challenge the vaccinated susceptible chickens. There was no corresponding increase in disease incidence when the virus passed in the vaccinated susceptible genetic line was used to challenge the vaccinated resistant line. From this series of experiments we show that a cloned MDV (Md5B40BAC) can be selected by serial IVP to induce greater disease incidence in vaccinated chickens. This increase in disease incidence occurs in both susceptible and resistant chicken lines but is more easily observed in the susceptible line. Not surprisingly, both host genetics and vaccination play a role in selecting for increased MDV virulence. Our results suggest that the progressive increase in MDV virulence is partially masked as it circulates through vaccinated resistant genetic lines, but by applying this virus to less-resistant genetic lines, virus evolution can be clearly observed. We would predict that the introduction of more-resistant genetic lines into a commercial house contaminated with MDV circulating through susceptible lines would be less likely to produce vaccine breaks than placing susceptible lines into a house in which previously the MDV was circulating through resistant genetic lines.

Differences in the early response of hatchlings of different chicken breeding lines to Salmonella enterica serovar Enteritidis infection

Poultry products are the major source of food-borne Salmonella infection in humans. Broiler lines selected to be more resistant to Salmonella could reduce the transfer of Salmonella to humans. To investigate differences in the susceptibility of newly hatched chicks to oral infection with Salmonellaenterica serovar Enteritidis, 3 commercial broiler lines (A, B, and C) were infected immediately after hatch and compared to healthy controls at 0.33, 1, and 2 d postinfection. Weight, bacteriological examination, and the jejunal influx of CD4, CD8, TCRαβ, TCRγδ, and KUL01 (macrophages and dendritic cells) cells that are positive was investigated. In addition, the jejunal transcriptional response was analyzed using whole-genome chicken cDNA arrays. Salmonella colony-forming unit counts from cecal content and liver revealed that Salmonella enterica entered the body at 0.33 d postinfection. Broiler line A appeared most susceptible to intestinal colonization and the systemic spread of Salmonella. In addition, the Salmonella-induced jejunal influx of macrophages in this line showed a clear increase in time, which is in contrast to lines B and C. On the other hand, all lines showed a peak of CD4+ cells at 1 d postinfection when infected chicks were compared to control chicks. The transcriptional response of line A clearly differed from the responses in lines B and C. Functional analysis indicated that the majority of the differentially expressed genes at 0.33 d postinfection in line A were involved in cell-cycle functions, whereas at 2 d postinfection the majority of the differentially expressed genes could be assigned to inflammatory disorder, differentiation and proliferation of (T) lymphocytes. These data indicate that hatchlings of different broiler lines differ in their systemic spread of Salmonella and suggest that intestinal barrier functions, as well as immunological responses, may be the underlying factors. We hypothesize that the differences between genetic chicken lines divergent in their response to Salmonella infection at a young age include developmental differences of the gut.

Gene Expression Analysis of Toll-Like Receptor Pathways in Heterophils from Genetic Chicken Lines that Differ in Their Susceptibility to Salmonella enteritidis.

Previously conducted studies using two chicken lines (A and B) show that line A birds have increased resistance to a number of bacterial and protozoan challenges and that heterophils isolated from line A birds are functionally more responsive. Furthermore, when stimulated with Toll-like receptor (TLR) agonists, heterophils from line A expressed a totally different cytokine and chemokine mRNA expression pattern than heterophils from line B. A large-scale gene expression profile using an Agilent 44K microarray on heterophils isolated from line A and line B also revealed significantly differential expression in many immune-related genes following Salmonella enteritidis (SE) stimulation, which included genes involved in the TLR pathway. Therefore, we hypothesize the differences between the lines result from distinctive TLR pathway signaling cascades that mediate heterophil function and, thus, innate immune responsiveness to SE. Using quantitative RT-PCR on mRNA from heterophils isolated from control and SE-stimulated heterophils of each line, we profiled the expression of all chicken homologous genes identified in a reference TLR pathway. Several differentially expressed genes found were involved in the TLR-induced My88-dependent pathway, showing higher gene expression in line A than line B heterophils following SE stimulation. These genes included the TLR genes TLR4, TLR15, TLR21, MD-2, the adaptor proteins Toll-interleukin 1 receptor domain-containing adaptor protein (TIRAP), Tumor necrosis factor-receptor associated factor 3 (TRAF3), the IκB kinases transforming growth factor-β-activating kinase 1 (TAK1), IKKε and IKKα, the transcription factors NFkB2 and interferon regulatory factor 7, phosphatidylinositol-3 kinase (PI-3K), and the mitogen-activated protein kinase p38. These results indicate that higher expression of TLR signaling activation of both MyD88-dependent and TRIF-dependent pathways are more beneficial to avian heterophil-mediated innate immunity and a complicated regulation of downstream adaptors is involved in stronger induction of a TLR-mediated innate response in the resistant line A. These findings identify new targets for genetic selection of chickens to increase resistance to bacterial infections.

Systemic response to Campylobacter jejuni infection by profiling gene transcription in the spleens of two genetic lines of chickens

Campylobacter jejuni (C. jejuni) is a leading cause of human bacterial enteritis worldwide with poultry products being a major source of C. jejuni contamination. The chicken is the natural reservoir of C. jejuni where bacteria colonize the digestive tract of poultry, but rarely cause symptoms of disease. To understand the systemic molecular response mechanisms to C. jejuni infection in chickens, total splenic RNA was isolated and applied to a whole genome chicken microarray for comparison between infected (I) and non-infected (N) chickens within and between genetic lines A and B. There were more total splenic host genes responding to the infection in resistant line A than in susceptible line B. Specifically, genes for lymphocyte activation, differentiation and humoral response, and Ig light and heavy chain were upregulated in the resistant line. In the susceptible line, genes for regulation of erythrocyte differentiation, hemopoiesis, and RNA biosynthetic process were all downregulated. An interaction analysis between genetic lines and treatment demonstrated distinct defense mechanisms between lines: the resistant line promoted apoptosis and cytochrome c release from mitochondria, whereas the susceptible line responded with a downregulation of both functions. This was the first time that such systemic defensive mechanisms against C. jejuni infection have been reported. The results of this study revealed novel molecular mechanisms of the systemic host responses to C. jejuni infection in chickens that warrant further investigation.

Heterophil functional responses to dietary immunomodulators vary in genetically distinct chicken lines

The effect of dietary supplementation of immunomodulators on in vitro chicken heterophil function was investigated using three diverse genetic lines of chickens (broiler, Fayoumi, and Leghorn). Dietary supplementation with β-glucan, ascorbic acid, and corticosterone was fed from 8 to 11 weeks of age. Heterophil function was evaluated weekly during supplementation using phagocytosis, bacterial killing, and heterophil extracellular traps (HETs)-DNA release. Fayoumis fed the basal diet had significantly higher HETs-DNA release ( P = 0.002) than Leghorns and broilers. Both genetic line and immunomodulator diet supplementation had significant effects on bacterial killing (line and diet effect: P < 0.001) and HETs-DNA release (line: P < 0.001; diet: P = 0.043). Dietary supplementation with immunomodulators, therefore, shows potential to affect and augment heterophil function in chickens. The current results also suggest the important role of genetics in innate immune responses.

Immune response gene expression in spleens of diverse chicken lines fed dietary immunomodulators

Vaccines, antibiotics, and other therapeutic agents used to combat disease in poultry generate recurring costs and the potential of residues in poultry products. Enhancing the immune response using alternative approaches such as selection for increased disease resistance or dietary immunomodulation may be effective additions to the portfolio of strategies the industry applies in poultry health management. The objective of this study was to characterize the effects of dietary supplementation with 3 immunomodulators [ascorbic acid, 1,3–1,6 β-glucans from baker's yeast, and corticosterone] on cytokine gene expression in the spleen of 3 distinct genetic lines of chickens. Relative mRNA expression levels were determined using quantitative reverse transcriptase PCR for IL-1β, IL-2, inducible nitric oxide synthase, and toll-like receptors 4 and 15, all of which play important roles in chicken immune function. Expression data were analyzed by mixed model analysis. The only significant effect detected was sex effect (P < 0.04) on expression of IL-1β. The present findings suggest the need for further investigations into the effects of dietary immunomodulators on cytokine gene expression in chickens so as to generate a better understanding of the immunomodulation process.

Evaluation of the bacterial community and intestinal development of different genetic lines of chickens

The gastrointestinal tract (GIT) of each animal species provides a unique niche for specialized intestinal bacterial communities to thrive, and in poultry this is no exception. However, little is known about how the bacterial community varies among these different genetic lines of chickens, especially of those with various growth rates. Therefore, an experiment was conducted to observe and evaluate the changes in the bacterial community and GIT development of a modern multipurpose strain, high-yield strain, and a historic strain, Athens Canadian Random Bred (ACR), of broilers. All birds were fed a standard nonmedicated corn-soybean meal broiler starter diet ad libitum from 0 to 35 d of age. Intestinal measurements and bacterial analysis of the ileum were conducted at 4, 8, 14, 21, and 35 d of age. Bacterial DNA was isolated from the digesta, and the distribution of bacterial 16S rRNA sequence polymorphisms was analyzed by a combination of denaturing gradient gel electrophoresis and terminal restriction fragment length polymorphisms. The multipurpose chicks performed the best from 0 to 14 d of age; however, overall performance was similar for the multipurpose and the high-yield broilers. The ACR birds had the poorest performance at all periods measured. The overall relative weight of the jejunum and ileum was not different between the 3 genetic lines, but the ACR birds had the longest relative jejunum and ileum lengths. Furthermore, the multipurpose birds had the longest villi height, whereas the ACR birds had the shortest villi height in the jejunum and ileum at all measuring periods. Based on denaturing gradient gel electrophoresis, the multipurpose and high-yield broilers had similar bacterial communities at all ages. Regardless of the genetic line of broiler, the bacterial community changed with age. Performance, GIT measurements, and bacterial community of the ACR differed compared with the modern broilers. The results indicate that the different genetic lines of broilers have varying rates of intestinal development, which may affect performance and the bacterial community.

Gene Expression Profiling of the Local Cecal Response of Genetic Chicken Lines That Differ in Their Susceptibility to Campylobacter jejuni Colonization

Campylobacter jejuni (C. jejuni) is one of the most common causes of human bacterial enteritis worldwide primarily due to contaminated poultry products. Previously, we found a significant difference in C. jejuni colonization in the ceca between two genetically distinct broiler lines (Line A (resistant) has less colony than line B (susceptible) on day 7 post inoculation). We hypothesize that different mechanisms between these two genetic lines may affect their ability to resist C. jejuni colonization in chickens. The molecular mechanisms of the local host response to C. jejuni colonization in chickens have not been well understood. In the present study, to profile the cecal gene expression in the response to C. jejuni colonization and to compare differences between two lines at the molecular level, RNA of ceca from two genetic lines of chickens (A and B) were applied to a chicken whole genome microarray for a pair-comparison between inoculated (I) and non-inoculated (N) chickens within each line and between lines. Our results demonstrated that metabolism process and insulin receptor signaling pathways are key contributors to the different response to C. jejuni colonization between lines A and B. With C. jejuni inoculation, lymphocyte activation and lymphoid organ development functions are important for line A host defenses, while cell differentiation, communication and signaling pathways are important for line B. Interestingly, circadian rhythm appears play a critical role in host response of the more resistant A line to C. jejuni colonization. A dramatic differential host response was observed between these two lines of chickens. The more susceptible line B chickens responded to C. jejuni inoculation with a dramatic up-regulation in lipid, glucose, and amino acid metabolism, which is undoubtedly for use in the response to the colonization with little or no change in immune host defenses. However, in more resistant line A birds the host defense responses were characterized by an up-regulation lymphocyte activation, probably by regulatory T cells and an increased expression of the NLR recognition receptor NALP1. To our knowledge, this is the first time each of these responses has been observed in the avian response to an intestinal bacterial pathogen.

Flow cytometric assessment of chicken T cell-mediated immune responses after Newcastle disease virus vaccination and challenge

The objective of this study was to use flow cytometry to assess chicken T cell-mediated immune responses. In this study two inbred genetic chicken lines (L130 and L133) were subjected to two times vaccination against Newcastle disease (ND) and a subsequent challenge by ND virus (NDV) infection. Despite a delayed NDV-specific antibody response to vaccination, L133 appeared to be better protected than L130 in the subsequent infection challenge as determined by the presence of viral genomes. Peripheral blood was analyzed by flow cytometry and responses in vaccinated/challenged birds were studied by 5-color immunophenotyping as well as by measuring the proliferative capacity of NDV-specific T cells after recall stimulation. Immunophenotyping identified L133 as having a significantly lower CD4/CD8 ratio and a lower frequency of γδ T cells than L130 in the peripheral T cell compartment. Furthermore, peripheral lymphocytes from L133 exhibited a significantly higher expression of CD44 and CD45 throughout the experiment. Interestingly, also vaccine-induced differences were observed in L133 as immune chickens had a significantly higher CD45 expression on their lymphocytes than the naïve controls. Immune chickens from both lines had a significantly higher frequency of circulating γδ T cells than the naïve controls both after vaccination and challenge. Finally, the proliferative capacity of peripheral CD4+ and CD8+ cells specific for NDV was addressed 3 weeks after vaccination and 1 week after infection and found to be significantly higher in L133 than in L130 at both sampling times. In conclusion, we found the applied flow cytometric methods very useful for the study of chicken T cell biology.

Comparison of gastrointestinal transit times between chickens from D+ and D− genetic lines selected for divergent digestion efficiency

D+ (high digestion efficiency) and D− (low digestion efficiency) genetic chicken lines selected for divergent digestion efficiency were compared in this experiment. Gizzard functions were tested in terms of digesta mean retention time and reactions to high dilution of a corn diet with 15% coarse sunflower hulls. The corn standard (S) and high fibre (F) experimental diets were given from 9 days of age to chickens from both lines. Besides the measurements of growth efficiencies (9 to 20 days), digestibilities (20 to 23 days) and gut anatomy (0, 9, 29, 42 and 63 days), two digestive transit studies were performed at 9 and 29 days of age. For the transit studies, the S and F diets were labelled with 0.5% TiO2 and 1% Cr-mordanted sunflower hulls. These diets were fed ad libitum during 3 days, and then the birds were euthanized. The digestive contents were analysed for the determination of marker concentrations and mean retention times (MRTs) in digestive compartments (crop + oesophagus, proventriculus + gizzard, duodenum + jejunum, ileum, rectum + cloaca and caeca) were determined. D+ birds were confirmed as better digesters than D− birds during the growth period, in association with larger gizzard and pancreas, and lighter small intestine in D+ than in D−birds. The MRT in the proventriculus-gizzard system, higher in D+ than in D− birds, was a major factor associated with differences between D+ and D− birds regarding digestion efficiencies and gut anatomy. Diet dilution with fibres reduced differences in digestion efficiencies and proventriculus-gizzard MRT between lines. Differences in gut anatomy between lines tended to disappear after 8 weeks of age. In conclusion, this study showed that MRT in the proventriculus-gizzard system was a major factor associated with genotype differences between the D+ and D− genetic chicken lines selected for divergent digestion efficiency, with longer MRT found in D+ than in D− birds.

Effects of diet particle size on digestive parameters in D+ and D− genetic chicken lines selected for divergent digestion efficiency

The aim of this experiment was to compare the D(+) and D(-) chicken lines genetically selected for divergent digestion efficiency by testing the effects of diet particle size on growth performances, digestion efficiencies, and digestive organ weights in both lines. A 2 x 3 factorial arrangement of treatments was used to test the D(+) and D(-) lines (sixth generation) and 3 diets, namely a pelleted standard corn diet (S), a pelleted hull diet (H) made by diluting S diet with 7% coarse cereal hulls, and a coarse corn diet (C) identical to the S diet, distributed as 30% coarsely crushed corn mixed with the 70% pelleted remaining part. Experimental diets were fed from 7 to 26 d of age. Combining results from all diets obtained at 26 d of age, D(+) birds showed 9% heavier (P < 0.0001) gizzard and 10% lighter (P < 0.0001) small intestine than D(-) birds. The AME(n) and digestibilities of lipids, protein, and starch measured at 3 wk of age were, on average, 3.5, 5.6, 5.8, and 0.5% higher (P < 0.0002) in D(+) than in D(-) birds, respectively. Significant (P </= 0.05) interactions between lines and diets were observed for AME(n) and digestibility values. Measured:calculated AME(n) ratio and digestibilities of protein and starch were improved (P < 0.05) by dietary coarse particles in D(-) birds, not in D(+) birds. Measured:calculated AME(n) ratio differed between lines by 6.0% with S diet versus 2.3% with H and C diets. In D(-) birds, the digestion increases due to coarse particles were associated with increased weights of gizzard (P < 0.0001) and pancreas (P < 0.05). In D(+) birds, coarse particles resulted in increased weights of gizzard (P < 0.0001) only. In conclusion, growth and functions of gizzard and pancreas needed to be stimulated by dietary coarse particles for optimum digestion efficiencies in D(-) chickens, whereas such stimulations were not needed in D(+) chickens. The D(+) chickens showed high digestion efficiencies in all cases, independently of diet particle size.

Effect of Selection for Resistance and Susceptibility to Viral Diseases on Concentrations of Dopamine and Immunological Parameters in Six-Week-Old Chickens

White Leghorn chickens were inbred respectively from their parent lines, which were diversely selected for resistance (line 63) or susceptibility (lines 72 and 15I5) to Marek’s disease and lymphoid leukosis. The differences in disease resistance may have been due to differential regulation of immune and neuroendocrine homeostasis. At 5 wk of age, chickens from the same line were randomly assigned to cages at 4 birds per cage. Blood samples were collected from the chickens at 6 wk of age (n = 10/line). Subsets of T lymphocytes (CD4+ and CD8+) and B cells were measured using flow cytometry. Concentrations of plasma IgG and dopamine were quantified with ELISA and HPLC assay, respectively. Line 63 chickens had a higher percentage of CD8+ cells but not CD4+ cells than the chickens of the lines 72 and 15I5 (P < 0.01). In contrast, both lines 72 and 15I5 had a greater percentage of B cells (P < 0.01). The concentrations of plasma IgG and dopamine were also regulated differently among the lines; both were in an order of 72 > 15I5 > 63 (P < 0.05 and P < 0.01, respectively). These results suggested that genetic selection for disease resistance also directly or indirectly modified the corresponding genetic components that govern the immune and neuroendocrine systems. The genetic lines of chickens may be used as animal models for investigation of the cellular mechanisms of genetic-environmental interactions on disease resistance.

Interference with the humoral immune response in diverse genetic lines of chickens II. The effect of colloidal carbon

Two experiments were conducted to study the difference in humoral immune responses between lines of chickens selected for high (H) or low (L) antibody production to sheep red blood cells (SRBC). Prior to i.v. immunization with SRBC or Brucella abortus (BA), chicks of both lines were injected with either 2, 3 or 4 ml carbon suspension (59 mg carbon/ml) per kg body weight; controls were not injected. In both the H and L line, a higher dose of carbon showed a more progressive depression of the total antibody titer to SRBC during the initial stage of the primary response. The 2ME-resistant antibody titers to SRBC showed the same tendency during the latter phase of the primary response. However, chicks treated with 3 ml carbon had lower 2ME-resistant antibody titers than any other group. Following i.m. reimmunization with SRBC, the previous treatment with carbon doses enhanced total antibody titers throughout the secondary response, when compared to the controls. The 3 ml carbon-treated chicks had the highest total anti-SRBC titers in the secondary response. The secondary 2ME-resistant anti-SRBC titers were not affected by the carbon doses. Carbon treatment did not affect the antibody titers toBA. No differences between the H and L line were found in the effects of carbon on the humoral immune responses to SRBC or BA.

Interference with the humoral immune response in diverse genetic lines of chickens: I. The Effect of Carrageenan

Two experiments were conducted in which the effect of carrageenan (CGN) on humoral immune response of chicks selected on either high (H) or low (L) antibody production to sheep red blood cells (SRBC) was determined. H and L line chicks were injected i.p. with different doses of CGN prior to immunization with SRBC or Brucella abortus (BA). Four weeks later chicks were reimmunized with the same antigens. In general, control H and L chicks had significantly higher total anti-SRBC titers than CGN-treated chicks in primary response. Also, total anti-BA titers were significantly higher in control chicks than CGN-treated chicks on days 3 and 5 following primary immunization and on days 0 and 7 of the secondary response. Overall, the 2-mercaptoethanol (2ME)-resistant anti-SRBC titers did not differ significantly among the CGN-treated groups. However, control chicks tended to have higher anti-BA 2ME-resistant titers from day 14 p.i. of primary response on. Regardless of antigen or CGN treatment, the H line chicks had significantly higher titers than L line chicks. However, the CGN treatments did not affect the antibody response to BA nor to SRBC differently between L and H line chicks. It would appear that since CGN is cytotoxic for macrophages, selection for antibody production did not result in different abilities of the macrophages of these chicken lines to respond to an antigenic challenge.

Purine metabolism in high and low uric acid lines of chickens: phosphoribosylpyrophosphate (PRPP) synthetase activities and PRPP pool sizes.

Phosphoribosylpyrophosphate synthetase activities were examined in liver and kidney tissues of two genetic lines of chickens selected for their plasma uric acid levels. Previous work demonstrated that the high uric acid line (HUA) has significantly greater de novo uric acid synthesis rates in kidney tissue compared to the low uric acid line (LUA). In addition, xanthine dehydrogenase activity in liver and kidney tissues was significantly higher in the HUA compared to the LUA line. The activity of PRPP synthetase, which provides a key substrate for the rate limiting step in de novo purine biosynthesis, was found to be significantly elevated (P less than 0.05) in liver and kidney tissues of the HUA line. The mean value of kidney PRPP synthetase activity was 30.2 +/- 0.7 nmole PRPP and 19.1 +/- 1.6 nmol PRPP produced/mg protein/hr, respectively, for the HUA and LUA lines. The PRPP pool size in kidney tissue was also significantly higher in the HUA line. The mean level of PRPP was 319.8 +/- 37.2 pmole/g of wet tissue compared to 176.7 +/- 12.4 pmole PRPP/g of wet tissue in the LUA line. The mean values of liver PRPP synthetase activities were 11.4 +/- 0.6 nmole PRPP and 9.0 +/- 0.4 nmole PRPP produced/mg protein/hr, respectively, for the HUA and LUA lines. The PRPP pool size in liver tissues was significantly higher in the HUA line as well. The mean level of PRPP was 550.7 +/- 72.5 pmole/g of wet tissue compared to 313.6 +/- 31.4 pmole PRPP/g of wet tissue in the LUA line. The enzyme from the HUA birds does not differ from controls with respect to Michaelis constants, inhibition phenomena, and phosphate activation. The increased PRPP synthetase activity found in HUA tissues may be due to structural alterations of the molecule resulting in an enzyme with a greater Vmax, an increase in the amount of enzyme protein, or a lowered level of a nondialyzable inhibitor.