Production traits and alloantigen systems in lines of chickens selected for high or low antibody responses to sheep erythrocytes

Growth of White Leghorn Chicken Immune Organs after Long-Term Divergent Selection for High or Low Antibody Response to Sheep Red Blood Cells

Long-term divergent selection from a common founder population for a single trait-antibody response to sheep erythrocytes 5 days post-injection-has resulted in two distinct lines of White Leghorn chickens with a well-documented difference in antibody titers: high (HAS)- and low (LAS)-antibody selected lines. Subpopulations-high (HAR)- and low (LAR)-antibody relaxed-were developed from generation 24 of the selected lines to relax selection. The objective of the current experiment was to determine if this long-term selection and relaxation of selection impacted the growth of two organs important to chicken immunity: the spleen and the bursa of Fabricius. Spleens and bursae were obtained from ten chickens per line at nine timepoints (E18, D0, D6, D13, D20, D35, D49, D63, and D91) throughout their rapid growth phase and presented as a percent of body weight. Significance was set at p ≤ 0.05. For the spleen, all lines consistently increased in size relative to body weight to D49, followed by a consistent decline. All lines had a similar growth pattern, but HAS spleens grew faster than LAS spleens. For the bursa, LAS was smaller than the other three lines as an embryo and also smaller than HAS through D63. In the selected lines, bursa weight peaked at D35, whereas the relaxed lines peaked at D49. By D91, there was no difference between lines. Artificial and natural selection, represented by the long-term selected and relaxed antibody lines, resulted in differences in the growth patterns and relative weights of the spleen and bursa of Fabricius.

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.

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.

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.

Genetic parameters of immune traits for Landrace and Large White pig breeds

Improving the immunocompetence towards pathogens represents a desirable objective of breeding strategies to increase resilience. However, the immune system is complex and the genetic foundation of the underlying components is not yet clarified. In the present study, we focused on 22 blood parameters of 1,144 Landrace (LR) and Large White (LW) piglets at the age of 6-7 weeks. The immune profiles covered immune cells, red blood cell characteristics and cytokines. Genetic parameters based on pedigree information along with possible environmental effects were estimated. Litter effects play an important role in the expression of immune parameters of their young progenies. Hence, litter impacts on the piglet's immune profile including the immune parameters of the dam itself were investigated by different models. To incorporate the complexity of the immune network, the data were further investigated with a principal component analysis. Immune traits showed low to high breed-specific heritabilities (h² ). Strong positive r_g were estimated among red blood cell characteristics (0.77-0.99) and among cytokines (0.48-0.99). Neutrophils and lymphocytes illustrated a high negative r_g (-0.96 to -0.98). The litter impact on piglet's immunity was examined and strengthened already observed breed differences. In LR, h² (0.22-0.15) and litter effect (c² ) (0.52-0.44) for IFN-γ decreased after statistical consideration of maternal impact. In LW, a decrease in h² (0.32-0.18) for IFN-γ and an increase in c² (0.54-0.56) were observed. Here, sufficient correlations were detected within various immune traits and functional biological networks of principal components. Most immune traits are heritable and are promising to cover global breed-specific immunocompetence in pigs. The analysis of immune traits has to be extended in order to find an optimal range and to characterize relationships between immunity and performance to gain an improved immune system without accidental losses in productivity.

Effects of a Bacterial Infection on Mitochondrial Function and Oxidative Stress in a Songbird

AbstractAs a major physiological mechanism involved in cellular renewal and repair, immune function is vital to the body's capacity to support tissue maintenance and organismal survival. Because immune defenses can be energetically expensive, the activities of metabolically active organs, such as the liver, are predicted to increase during infection by most pathogens. However, some pathogens are immunosuppressive, which might reduce the metabolic capacities of select organs to suppress immune response. Mycoplasma gallisepticum (MG) is a well-known immunosuppressive bacterium that infects domestic chickens and turkeys as well as songbirds. In the house finch (Haemorhous mexicanus), which is the primary host for MG among songbird species, MG infects both the respiratory system and the conjunctiva of the eye, causing conspicuous swelling. To study the effect of a systemic bacterial infection on cellular respiration and oxidative damage in the house finch, we measured mitochondrial respiration, mitochondrial membrane potential, reactive oxygen species production, and oxidative damage in the livers of house finches that were wild caught and either infected with MG, as indicated by genetic screening for the pathogen, or free of MG infection. We observed that MG-infected house finches showed significantly lower oxidative lipid and protein damage in liver tissue compared with their uninfected counterparts. Moreover, using complex II substrates, we documented a nonsignificant trend for lower state 3 respiration of liver mitochondria in MG-infected house finches compared with uninfected house finches (P=0.07). These results are consistent with the hypothesis that MG suppresses organ function in susceptible hosts.

Major histocompatibility complex recombinant R13 antibody response against bovine red blood cells

Recombination within the chicken major histocompatibility complex (MHC) has enabled more precise identification of genes controlling immune responses. Chicken MHC genes include BF, MHC class I; BL, MHC class II; and BG, MHC class IV that are closely linked on chromosome 16. A new recombination occurred during the 10th backcross generation to develop congenic lines on the inbred Line UCD 003 (B17B17) background. Recombinant R13 (BF17-BG23) was found in a single male chick from the Line 003.R1 (BF24-BG23) backcross. An additional backcross of this male to Line UCD 003 females increased the number of R13 individuals. Two trials tested this new recombinant for antibody production against the T cell-dependent antigen, bovine red blood cells. Fifty-one progeny segregating for R13R13 (n = 10), R13B17 (n = 26), and B17B17 (n = 15) genotypes were produced by a single R13B17 male mated to 5 R13B17 dams. One milliliter of 2.5% bovine red blood cell was injected intravenously into all genotypes at 4 and 11 wk of age to stimulate primary and secondary immune responses, respectively. Blood samples were collected 7 d after injection. Serum total and mercaptoethanol-resistant antibodies against bovine red blood cell were measured by microtiter methods. The least squares ANOVA used to evaluate all antibody titers included trial and B genotype as main effects. Significant means were separated by Fisher's protected least significant difference at P < 0.05. R13R13 chickens had significantly lower primary total and mercaptoethanol-resistant antibodies than did the R13B17 and B17B17 genotypes. Secondary total and mercaptoethanol-resistant antibodies were significantly lower in R13R13 chickens than in R13B17 but not B17B17 chickens. Gene differences generated through recombination impacted the antibody response of R13 compared with B17. Secondary antibody titers were not substantially higher than the primary titers suggesting that the memory response had waned in the 7-wk interval between injections. Overall, the results suggest that the lower antibody response in R13R13 homozygotes may be caused by recombination affecting a region that contributes to higher antibody response.

The effects of vaccination with keyhole limpet hemocyanin or oral administration of Salmonella enterica serovar Enteritidis on the growth performance of immunoglobulin knockout chickens

The nutritional cost of activating B cell-mediated immunity is thought to be low in chickens. However, this assumption is incompletely characterized. Immunoglobulin knockout (Ig-KO) chickens lacking B cells and immunoglobulin may potentially be a robust model to investigate the nutritional cost of immunity. Specifically, comparing the growth of Ig-KO chickens to immunocompetent birds (WT) following activation of the immune system should indicate costs associated with B cell-mediated immunity. A total of 3 experiments were conducted to determine if (1) an antibody response to keyhole limpet hemocyanin (KLH), (2) an intra-abdominal injection with Salmonella enterica serovar Enteritidis (SE), or (3) an oral challenge of SE would affect body weight gain (BWG) in homozygous Ig-KO (KO) chickens and their immunocompetent counterparts. In Experiment 1, a significant genotype*vaccination status interaction was observed (P = 0.03) during the period from 0 to 6 D after initial vaccination in which KLH injection reduced BWG in WT birds, but not in KO birds. A genotype*vaccination status interaction was present (P = 0.002) from 0 to 7 D after the first booster in which KLH injection due to reduced BWG in KO birds, but not WT birds. In Experiment 2, both KO and immunocompetent birds lost body weight during the period from 0 to 2 D after the SE injection, with no significant differences due to genotype (P = 0.92). Experiment 3 demonstrated that KO birds gained less weight than immunocompetent birds, with a tendency for less weight gain after an initial challenge (P = 0.07) and significantly so after a secondary challenge (P = 0.03). The results from these experiments collectively demonstrate that B cell-mediated immunity can affect growth performance in chickens. Furthermore, these effects can either preserve or impair growth performance, likely via mechanisms related to the immune response rather than the discrete nutritional cost of B cell-mediated immunity.

Dwarf chickens with low monocytes/macrophages phagocytic activity show low antibody titers but greater performance

Monocytes/macrophages phagocytosis has key roles in inflammatory responses. However, systematic research on the effects of monocytes/macrophages phagocytosis on production and reproductive performance in dwarf chickens is lacking. In this study, we developed the HCT-8-MTT method to detect monocytes/macrophages phagocytosis product (PP) which was accuracy, flexible, and saving time. Based on PP in 990 dwarf chickens (890 hens and 100 cocks), chickens were divided into high phagocytosis product group (HPPG) and low phagocytosis product group (LPPG). In production performance, chickens in LPPG have higher laying rate at 24 wk and 71 wk and higher average egg weight at 23 wk and 24 wk than in HPPG (P < 0.05). The levels of follicle-stimulating hormone and luteinizing hormone were higher in LPPG than in HPPG at 58 wk (P < 0.01). In the reproductive performance, the fertilization rate in LPPG was higher than that in HPPG at 45 wk, 49 wk, and 53 wk (P < 0.05). Chickens in LPPG have higher hatchability than HPPG at 45 wk and 49 wk (P < 0.05). In LPPG, the mRNA expression levels of follicle-stimulating hormone receptor and CD9 in the follicle were higher than HPPG (P < 0.05). In the immune response, chickens with higher PP levels showed higher antibody titers for the avian influenza virus H9 inactivated vaccine (P < 0.01). Therefore, monocytes/macrophages PP was positively associated with antibody titers and negatively related to production and reproductive performance, and these findings have practical applications for the optimization of production in the poultry industry.

Relationships between genetic change and infectious disease in domestic livestock

The relations between genetic change in domestic livestock and infectious disease (including both its epidemiology and the animal's reaction to it) are examined. The overall picture is confusing because there are different, and seemingly unrelated, ways of considering the issue. An attempt is made to put these together into a more general framework. Four processes of particular interest are distinguished and discussed in more detail: (i) the way a population's genetic potential for immunocompetence can be changed by breeding, (ii) the way an animal's immunocompetence is influenced by that animal's production potential, in combination with the environmental resources that are available to it at a given time, (iii) the way the disease status of an animal (and a population of animals) is influenced by its immunocompetence, and (iv) the way the production level of an animal is influenced by activation of its immune system. Ultimately, all four processes influence the realised level of production.

This comes down to four questions that need to be addressed: (i) can we use genetic variation in immunocompetence in animal breeding? (ii) does a higher production potential (today's direction of breeding) have a negative impact on immunocompetence? (iii) does improved immunocompetence result in improved health? and (iv) how large is the negative impact of disease on production?

Correlation of innate immunocompetence traits with economic traits in various indigenous and exotic breeds of chicken

Birds (433) were utilized for investigation at 7 weeks of age and at 45 weeks of age (119). The immunological traits measured included humoral response like HA, MER and MES; non-specific immune responses like CPW and APW complement and PI and CMI response. In two broiler lines, body weight at 6, 7, 8, 9 and 10 weeks of age were measured in addition to body weight at hatch and feed efficiency to 10 weeks of age. In rest of the genetic groups, the economic traits measured included day old body weight, body weight, shank length and keel length at 5, 10, 15 and 20 weeks of age, age at sexual maturity, egg production as number of eggs to 40 weeks of age, egg weight at 40 weeks of age, per cent mortality during different periods up to 20 weeks of age, feed consumption per day, and feed conversion ratio to produce a dozen of eggs or a kg of egg mass. All the traits were measured on individual birds except for per cent mortality and feed efficiency in broilers. For evaluation of humoral and nonspecific responses except PI, the birds were immunized with sheep red blood cells (SRBCS) by injecting 1 ml of 25% (v/v) SRBCs suspension in PBS intramuscularly in thigh muscle. The various components of immunocompetence parameters like humoral and nonspecific responses were measured on day 5, 12 and 19-post immunization. Natural antibodies for various immunocompetence traits were also measured on the day of SRBC injection. For evaluation of effect of age, birds of the Aseel, Kadakanath, Naked Neck and Frizzle were immunized against SRBCs at 45 weeks of age and immunocompetence traits were measured on day 0 and 7 p.i. CMI response was estimated by injecting 0.1 ml of PHA-P interdigitally (100 μg PHA-P/0.1 ml of PBS) between the 3rd and 4th toe of the right foot of each chicken as Foot index (FI) and was estimated by measuring the skin swelling. Data so collected were analyzed statistically utilizing appropriate statistical procedures to evaluate correlation coefficients among immunological and economic traits calculated as simple product moment correlation. HA was positively correlated with MER, CPW and APW and negatively correlated with FI and PI. The trend remained the same on all the days of study. The correlation of MER with CPW and APW were mostly positive and did not present any definite trend in both magnitude and direction with FI and PI. The correlations between CPW and APW were positive and highly significant. No definite trend was observed for the correlation between CPW with FI and PI. The trend remained the same for APW also. FI and PI were negatively correlated in indigenous breeds and broilers but positively correlated in Dahlem Red and White Leghorns. Irrespective of direction, all the estimates were small. HA was seen to be positively correlated with body weight, shank length, keel length, ASM and negatively correlated with egg production and mortality. MER was positively correlated with body weight, shank length, keel length and ASM and negatively correlated with egg production and mortality. The relationship of FI and PI with body weight, shank length, and keel length was negative. Relation between FI and egg production was negative. The relationship of immunocompetence traits with economic traits presented in the literature as well as realized in this study did not lead to any definite conclusion suggesting more study to quantify the magnitude and direction of relationship for their use in practical breeding programmes.

Genome-wide standing variation facilitates long-term response to bidirectional selection for antibody response in chickens

Background

Long-term selection experiments provide a powerful approach to gain empirical insights into adaptation, allowing researchers to uncover the targets of selection and infer their contributions to the mode and tempo of adaptation. Here we implement a pooled genome re-sequencing approach to investigate the consequences of 39 generations of bidirectional selection in White Leghorn chickens on a humoral immune trait: antibody response to sheep red blood cells.

Results

We observed wide genome involvement in response to this selection regime. Many genomic regions were highly differentiated resulting from this experimental selection regime, an involvement of up to 20% of the chicken genome (208.8 Mb). While genetic drift has certainly contributed to this, we implement gene ontology, association analysis and population simulations to increase our confidence in candidate selective sweeps. Three strong candidate genes, MHC, SEMA5A and TGFBR2, are also presented.

Conclusions

The extensive genomic changes highlight the polygenic genetic architecture of antibody response in these chicken populations, which are derived from a common founder population, demonstrating the extent of standing immunogenetic variation available at the onset of selection.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3414-7) contains supplementary material, which is available to authorized users.

Immunocompetence and resistance to marble spleen disease of broiler- and layer-type pure lines of chickens

The intent of this study was to evaluate, under concurrent conditions, certain responses that may be important in chicken breeding and growing. Three commercial broiler pure lines (A, B, and C) and two experimental White Leghorn lines selected for high (HAS) and low (LAS) antibody response to sheep red blood cells were evaluated concurrently for humoral and cell-mediated immunocompetence, resistance to marble spleen disease virus (MSDV), relative asymmetry (RA), and comb weight. Chicks were injected with 0.1 ml of 0.25% SRBC at 21 days of age. Antibody response 6 days after injection was highest in line HAS. Titres for the commercial lines were similar to those in line LAS. The cutaneous basophil hypersensitivity test, an in vivo cell-mediated immune response, was measured as the increase in toe-web thickness 24 h after an injection with T-cell mitogen phytohaemagglutinin (PHA)-P or -M into a sample of chicks at 9 days of age and a different sample of chicks at 20 days of age. PHA-P elicited greater responses than PHA-M at both ages. The pattern among stocks, however, differed depending upon age. Responses at 9 days were greater for the Leghorn than broiler lines, while at 20 days, responses were greater in lines A and LAS than in lines B, C, and HAS. Resistance to MSDV challenge differed among stocks, with the ranking for resistance being C>(A=B=LAS)>HAS. Rankings of RA for normal thickness of the toe web between the third and fourth digits at 9 days of age were (HAS=LAS)>(A=B=C). There were no differences in RA among stocks at 20 days of age. There was a significant line by sex interaction for relative comb weight, due to differences between lines for males but not females. Data from this study suggest that competence in one arm of the immune system is not a reliable measure of general immunocompetence, nor is it a measure of resistance in general.

Immune effects of chicken non-MHC alloantigens

Alloantigen systems are a broad group of molecules found on various cell types, including erythrocytes and lymphocytes. These alloantigens, identified via specific polyclonal or monoclonal antibodies or molecular methods, have demonstrated effects on immune responses. Erythrocyte alloantigens include the A, B, C, D, E, H, I, J, K, L, N, P, and R systems. Highly polymorphic alloantigen B has been identified as the chicken major histocompatibility complex (MHC). The other twelve systems have a variable degree of polymorphism as well as impact on immune measurements or responses against pathogens. Selection for immune characters altered allele frequencies for particular alloantigen systems. Three lymphocyte alloantigens, Bu-1, Ly-4 and Th-1 have more limited polymorphism but still influence responses against viral pathogens, Rous sarcoma virus and Marek's disease. Together, these erythrocyte and lymphocyte systems contribute to the overall immunity. Identification of the specific alloantigen proteins remains crucial to understanding their immune contribution.

Coral snake antivenom produced in chickens (Gallus domesticus)

The production of anti-snake venom from large mammal's blood has been found to be low-yielding and arduous, consequently, antivenom immunoglobulins for treatment are achieved regularly as polyvalent serum. We have standardized an undemanding technique for making purified immunoglobulin IgY antivenom consisting of polyclonal antibodies against coral snake venom in the egg yolk of immunized hens. We have adapted a reported process of antibody purification from egg yolks, and achieved 90% antibody purity. The customized technique consisted of the removal of lipids from distilled water-diluted egg yolks by a freeze–thaw sequence. The specific immunoglobulins were present in the egg yolk for up to 180 days postimmunization. Therefore, by means of small venom quantities, a significant amount of immunoglobulins were found in an adequately purified state (The obtained material contained about 90% pure IgY). The antigen binding of the immunoglobulins was detected by a double immunodiffusion test. Titers of antibodies in the yolk were estimated with a serum protection assay (Median effective dose = ED₅₀) (ED₅₀= 477 mg/kg). Given that breeding hens is economically feasible, egg gathering is noninvasive and the purification of IgY antibodies is quick and easy, chicken immunization is an excellent alternative for the production of polyclonal antibodies. To the best of our knowledge, this is the first coral snake antivenom prepared in birds.

Do social mating systems limit maternal immune investment in shorebirds?

Across mating systems, females differ in the amount of resources they invest in offspring. For example, polyandrous females invest in acquiring multiple matings rather than providing parental care. We examined how the amount of maternal immune investment, measured as immunoglobulin Y and lysozyme activity in eggs, was influenced by female role across three social mating systems (polyandry, polygyny, and monogamy) in shorebirds. We predicted that polyandry should impose the greatest costs on the ability to provision eggs and monogamy, where females receive benefits from biparentality, the least. Contrary to our predictions, levels of maternally derived egg immune constituents were consistently high across measures in the polyandrous species and low in the monogamous species. Our results may support a link with pace-of-life where developmental costs are greater than the energetic costs of provisioning eggs, and (or) a role for sexual selection acting on maternal immune investment.

Egg quality traits differ in hens selected for high as compared with low antibody response to sheep red blood cells

White Leghorn chickens were selected for 36 generations for high (HAS) or low (LAS) antibody response to SRBC 5 d after an intravenous challenge. Our objective was to determine differences in egg quality resulting from that selection. In total, eggs from 45 hens from each line were assessed for shape index (SI), weight (WT, g), albumen height (AH, mm), Haugh units (HU), yolk color (YC), and eggshell weight (ESW, g) and thickness (EST, mm). Three cycles representing early, middle, and late stages of production were examined. Eggs from HAS hens had higher SI scores (4.12 ± 0.55; P < 0.001) and greater AH (0.27 ± 0.12; P < 0.001) and HU (1.89 ± 0.91; P = 0.04) than LAS hens; conversely, eggs from LAS hens had greater EST (0.03 ± 0.01 g; P < 0.001) and heavier ESW (0.66 ± 0.09 g; P < 0.001) than HAS hens. Lines were similar for WT and YC (P > 0.52). Albumen height and HU decreased (P < 0.001), whereas WT, ESW, and EST increased (P < 0.001) over cycles for both lines. However, SI decreased in LAS hens, yet increased in HAS hens, across cycles (P < 0.001). An interaction between line and cycle was observed in WT, SI, ESW, and EST (P < 0.001), but only for WT did the interaction cause re-ranking across cycles. Egg quality was, generally, superior in HAS compared with LAS hens, suggesting that higher antibody response may maintain overall fitness.

Immune response from a resource allocation perspective

The immune system is a life history trait that can be expected to trade off against other life history traits. Whether or not a trait is considered to be a life history trait has consequences for the expectation on how it responds to natural selection and evolution; in addition, it may have consequences for the outcome of artificial selection when it is included in the breeding objective. The immune system involved in pathogen resistance comprises multiple mechanisms that define a host's defensive capacity. Immune resistance involves employing mechanisms that either prevent pathogens from invading or eliminate the pathogens when they do invade. On the other hand, tolerance involves limiting the damage that is caused by the infection. Both tolerance and resistance traits require (re)allocation of resources and carry physiological costs. Examples of trade-offs between immune function and growth, reproduction and stress response are provided in this review, in addition to consequences of selection for increased production on immune function and vice versa. Reaction norms are used to deal with questions of immune resistance vs. tolerance to pathogens that relate host health to infection intensity. In essence, selection for immune tolerance in livestock is a particular case of selection for animal robustness. Since breeding goals that include robustness traits are required in the implementation of more sustainable agricultural production systems, it is of interest to investigate whether immune tolerance is a robustness trait that is positively correlated with overall animal robustness. Considerably more research is needed to estimate the shapes of the cost functions of different immune strategies, and investigate trade-offs and cross-over benefits of selection for disease resistance and/or disease tolerance in livestock production.

Reproductive soundness is higher in chickens selected for low as compared with high antibody response

White Leghorn chickens were selected for 36 generations for high (HAS) or low (LAS) antibody response to SRBC 5 d after an intravenous challenge. The aim of this study was to investigate possible changes in reproductive soundness resulting from that selection. Age and BW at onset of lay (first egg), along with weight of the first egg, were recorded on 45 hens from each line. Intensity of lay was measured as the number of ovulations within a 15-d period over 15 sequential intervals (total 225 d). Three cycles of fertility also were assessed, coinciding with early, middle, and late production stages. For fertility of males and females within a line to be independently evaluated, roosters and hens were mated by artificial insemination to an unrelated control line of White Plymouth Rocks. Twenty roosters from each antibody line were considered, as well as the 45 hens. Pooled semen from the control line was used for mating the hens from the antibody lines. Hens from the LAS line commenced lay at a younger age (11.67±3.53 d; P<0.001), lighter BW (-169.46±40.20 g; P<0.001), and with greater intensity (2.68±0.25%; P=0.001) than those from the HAS line. Any differences in intensity thereafter were trivial between lines (P=0.42), with intensity decreasing sharply toward the end of the 7-mo production period in both lines. Length of fertility differed between hens of the antibody lines during the first cycle (3.35±0.85 d; P=0.002) and between roosters during the first (3.58±1.06 d; P=0.02) and second (3.38±1.07 d; P=0.03) cycles, with chickens from the LAS line having the longer length of fertility in both sexes. A correlated response in reproductive soundness to divergent selection for antibody response was observed. This may in part be due to differences in resource allocations, with particular impact on duration of fertility.

Phenotypic responses of chickens to long-term selection for high or low antibody titers to sheep red blood cells

A long-term bidirectional selection experiment was conducted to study antibody response to SRBC. Lines, high antibody selection (HAS) and low antibody selection (LAS), originating from the same White Leghorn base population had undergone 37 generations of selection for either high or low antibody response 5 d after a single intravenous injection of 0.1 mL of a 0.25% suspension of SRBC antigen. Subpopulations, where selection was relaxed, were maintained as contemporaries with the selected lines from generations 16 to 24 [high antibody relaxed (HAR) and low antibody relaxed (LAR)] and 24 to 37. Body weights were obtained at 4, 24, and 38 wk of age and at the onset of lay (BW at first egg). Also measured were age in days to first egg, percentages of hen-day ovulations and normal egg production, and percentages of normal and defective eggs from total ovulation (PNE and PDE). Selection lead to a large divergence in antibody titers between the selected lines, with a plateau reached in line LAS. Line HAS and HAR females displayed higher antibody titers, lower BW4, and matured at older ages than those from LAS and LAR (P < 0.05). Correlations between BW at 4 wk and antibody titers were different between the selected lines, being positive in line LAS and negative in line HAS. Quadratic regression models fit well with antibody titers, BW4, and PNE, with limiting values for these traits calculated based on regression curves. For line HAS, plots showed that an increased tendency of antibody titers was followed by decreased BW4 and increased PNE. For line LAS, however, antibody titers and BW4 decreased in parallel while PNE increased. It appears that at the phenotypic level there was a resource balance between immune response, growth, and reproductive traits, which during long-term selection, individuals altered their dynamic of resource allocations to satisfy certain needs.

Liver enzymes in White Leghorns selected for the sheep red blood cell immune response

Liver enzymes are essential to xenobiotic metabolism. Expression of these enzymes is dependent upon factors such as age and sex. The objective of this study was to determine basal liver enzyme levels in male and female White Leghorn chickens to provide reference values for future studies. Chickens from 2 lines divergently selected for 35 generations for high antibody and low antibody immune response to SRBC were used. Six male and 6 female chickens from each line were killed at each of 4, 8, 12, and 20 wk of age. Livers were collected and used for enzyme analyses. Liver tissue was analyzed for quinone reductase, glutathione-S-transferase, and cytochrome P450 3A4 activity. All data were analyzed using ANOVA. There were no consistent differences in enzyme activity between high- and low-antibody lines at any age. Cytochrome P450 3A4 activity was substantially greater in 4- and 8-wk than in 12- and 20-wk-old chickens (P < 0.001). This study provides insights into enzyme activities of liver enzymes; however, except for cytochrome P450 3A4, no clear trends across ages were observed.

Comparative genome analysis with the human genome reveals chicken genes associated with fatness and body weight

The selection of meat-type chickens (broilers) for rapid growth has been accompanied by excessive fat deposition. In this study, we analysed 53 candidate genes that are associated with obesity and obesity-related traits in humans, for which we found chicken orthologues by BLAST searches. We have identified single nucleotide polymorphisms (SNPs) with significant differences in allele frequencies between broilers and layers in each of the following six candidate genes: adrenergic, beta-2-, receptor, surface (ADRB2); melanocortin 5 receptor (MC5R); leptin receptor (LEPR), McKusick-Kaufman syndrome (MKKS), milk fat globule-EGF factor 8 protein (MFGE8) and adenylate kinase 1 (AK1). To examine associations with fatness and/or body weight, we used birds of extreme phenotypes in F(2) and backcross populations with varying levels of abdominal fat weight per cent (%AFW) and body weight. We then assessed the level of gene expression by real-time PCR. In two genes, ADRB2 and MFGE8, we found significant association with %AFW. The ADRB2 gene was found to have a significantly higher expression in the liver of lean chickens compared with those of the fat individuals. We believe that this approach can be applied for the identification of other quantitative genes.

Effects of silymarin on gossypol toxicosis in divergent lines of chickens

Gossypol, a pigment of cotton, is a hepatic toxin for chickens. Thus, despite its high protein content, inclusion of cottonseed meal in poultry diets is problematic. Silymarin, an extract from milk thistle, has hepatoprotective qualities and could potentially serve as a feed additive to offset the toxicity of gossypol. The objective of this study was to determine if silymarin could counteract gossypol toxicosis. Cockerels (n = 144) from lines divergently selected for humoral immunity were used. Three individuals from each line were randomly assigned to a cage and fed a corn-soybean meal (control) diet for 14 d. Six cages per line were then randomly assigned 1 of 4 dietary treatments (1,000 mg/kg of gossypol, 1,000 mg/kg of silymarin, 1,000 mg/kg of both gossypol and silymarin, or a control diet). Body weight and feed intake data were collected for 21 d, with chickens bled weekly to collect plasma and determine hematocrits. Chickens were then killed, and livers were collected for subsequent histology and enzymatic activity analyses. Endpoints measured weekly were analyzed with repeated measures and regression methodologies. Plasma and liver enzyme activities, and histological measures, were analyzed using ANOVA. No significant interactions between diets and lines were observed. Chickens assigned to the gossypol and gossypol-silymarin diets stopped gaining weight at d 14 (P < 0.001) and lost weight by d 21 (P < 0.001). Gamma glutamyltransferase was also elevated in these chickens at d 14; activities increased further by d 21 (P < 0.001). Histological examination of liver slices indicated substantial lipidosis (P < 0.001). Furthermore, quinone reductase activity was higher in gossypol- and gossypol-silymarin-treated chickens than in control and silymarin-treated chickens (P < 0.001). Silymarin did not alleviate any clinical effects of gossypol toxicosis.

Genetics of immunocompetent traits in a synthetic broiler dam line

Three hundred and three chicks of both sexes, from a synthetic dam line (SDL) of broiler chickens, were studied for economic traits (body weights at 4, 5 and 6 weeks of age) and immunological traits (humoral and cell mediated immune responses, and serum lysozyme concentration). The objective was to evaluate these traits and to estimate their genetic and non-genetic parameters. The humoral immune response was assessed by estimating the antibody response to sheep red blood cells using the haemagglutination (HA) test and serum IgG concentration using single radial immunodiffusion (SRID). The cell mediated immune (CMI) response was estimated as in vivo response to a mitogen (PHA-P). Serum lysozyme was measured by lysoplate assay. Least squares means for body weight at 4, 5 and 6 weeks were 684 +/- 20, 920 +/- 19 and 1205 +/- 28 g, HA titre was 6.289 +/- 0.246, CMI was 0.438 +/- 0.015 mm, lysozyme was 1.860 +/- 0.047 microg/ml and IgG was 6.287 +/- 0.194 mg/ml. There was an effect of sire on HA titre and on body weight at 4, 5 and 6 weeks of age; males were heavier than females. Heritability estimates were high for body weights but low for immunological traits. Phenotypic correlations (rp) among body weights were high and positive but were very low between body weights and most immunological traits. Among the immunological traits all rp were very low. Genetic correlations (rg) of body weights were positive and medium to high with CMI and HA and negative with serum IgG.

Genetic parameters for levels of natural antibodies in chicken lines divergently selected for specific antibody response

The present study estimated the heritability of natural antibody (NAb) levels binding rabbit red blood cells at the day of immunization with SRBC (NAb0) and 5 d postimmunization (NAb5) in 2 chicken lines divergently selected for specific antibody levels (SpAb) against SRBC and a randombred control line. In addition, genetic correlations between the levels of NAb binding rabbit red blood cells and levels of SpAb binding SRBC were estimated. The heritability of the SpAb level against SRBC was estimated based on data from 23 generations of selection and in total 21,842 chickens. The heritability of NAb levels against rabbit red blood cells was estimated on 1,764 chickens in generations 22 and 23 using a bivariate analysis including the trait under selection (i.e., SpAb responses to SRBC). Maternal environmental effects were accounted for in the analyses. The heritability for SpAb was 0.17, the heritability for NAb0 levels was 0.23, and the heritability for NAb5 was 0.09. The genetic correlation between SpAb and NAb0 was 0.15 and the genetic correlation between SpAb and NAb5 was 0.50. The weak, though positive, genetic correlation between SpAb responses and the NAb0 levels in nonimmunized chickens, as well as the moderate genetic correlation between SpAb responses and the NAb levels 5 d postimmunization with SRBC, suggest that selection for enhanced adaptive immune system results in a positive correlated response of the innate immunity of chickens.

Transgenerational priming of immunity: maternal exposure to a bacterial antigen enhances offspring humoral immunity

Young vertebrates have limited capacity to synthesize antibodies and are dependent on the protection of maternally transmitted antibodies for humoral disease resistance early in life. However, mothers may enhance fitness by priming their offspring's immune systems to elevate disease resistance. Transgenerational induced defences have been documented in plants and invertebrates, but maternal priming of offspring immunity in vertebrates has been essentially neglected. To test the ability of mothers to stimulate the immune systems of offspring, we manipulated maternal and offspring antigen exposure in a wild population of birds, pied flycatchers (Ficedula hypoleuca). We show that immunization of the mother before egg laying apparently stimulates a transgenerational defence against pathogens by elevating endogenous offspring antibody production. If the disease environments encountered by mothers and offspring are similar, this transgenerational immune priming may allow young to better cope with the local pathogen fauna.

Identification of a single nucleotide polymorphism of the insulin-like growth factor binding protein 2 gene and its association with growth and body composition traits in the chicken

Insulin-like growth factor binding protein 2 regulates a broad spectrum of biological activities involved in growth, development, and differentiation. The current study was designed to investigate the associations of IGFBP2 gene polymorphisms with chicken growth and body composition traits. The Northeast Agricultural University Resource Population (NEAURP) was established by crossing broiler sires, derived from lines at Northeast Agricultural University, that were divergently selected for abdominal fat, with Baier layer dams, a Chinese local breed. The F1 birds were inter-crossed to produce an F2 population. Body weight and body composition traits were measured in the NEAURP. The PCR primers for the intron 2 region of IGFBP2 were designed based on chicken genomic sequence. Nucleotide polymorphisms between parental lines were detected by DNA sequencing. A C/T SNP in intron 2 was detected, and PCR-RFLP methods were then developed to genotype the F2 individuals. The results showed that the IGFBP2 SNP was associated with multiple traits, including BW, metatarsus length, shank length, femur length, shank weight, femur weight, metatarsus claw weight, and abdominal fat weight in the 1,028 NEAURP F2 individuals. This research suggests that IGFBP2 or a tightly linked gene has broad effects on growth and development in the chicken.

Antibody Response of Chickens to Sheep Red Blood Cells: Crosses Among Divergently Selected Lines and Relaxed Sublines

Crosses were made among lines of chickens that had undergone 30 generations of selection for high or low antibody response 5 d after an intravenous injection with SRBC, and between sublines in which selection was relaxed in generation 24. Antibody responses at 5, 10, and 14 d after injection were measured in the 4 lines and in reciprocal crosses among them. Divergence between the high and low lines selected for SRBC antibody was immediate and increased during selection. Although significant in both cases, separation of the relaxed subline from its respective selected line was greater in the high than the low line. Five-day SRBC titers of the relaxed lines and the crosses were intermediate to the high and low selected lines, with the direction and magnitude of heterosis being line dependent. A high proportion of chickens from low line mating combinations did not have detectable antibody titers at 10 and 14 d postinoculation with SRBC, precluding statistical analysis of these data. Results are discussed in the context of intra- and interlocus effects on the selected trait.

Correlation analysis between single-nucleotide polymorphism of malate dehydrogenase gene 5'-flanking region and growth and body composition traits in chicken

Malate dehydrogenase (MD) is a key enzyme that plays an important role in energy metabolism. It catalyzes the oxidative decarboxylation of L-malate to yield CO2 and pyruvate, while simultaneously generating NADPH from NADP+. The NADPH generated can be utilized in de novo synthesis of palmitate, which is the precursor molecule for the formation of other long-chain fatty acids. And high levels of MD will also activate muscle development. The current study was designed to investigate the effects of MD gene on growth and body-composition traits in chicken. The eighth generation population of Northeast Agricultural University broiler lines divergently selected for its abdominal fat and Northeast Agricultural University F2 resource population were used in the research. Polymorphisms were detected by DNA sequencing and PCR-RFLP method was then developed to screen the population. A single mutation at the position of the 235 bp (Accession No. U49693) of MD 5'-flanking region was found. The correlation analysis between the polymorphism of the MD gene and growth and body composition traits was carried out using the appropriate statistic model. Least-square analysis showed that the BB genotype birds had much higher pectoralis major weight and percentage of pectoralis major than AA genotype birds (P<0.05). The abdominal fat weight, percentage of abdominal fat, the liver weight and percentage of liver weight of the AA genotype birds were much higher than those of BB genotype birds (P<0.05). These results indicate that MD gene is the major gene or is linked to the major gene that affects the growth and body composition traits in chicken.

Memory antibody responses of broiler and leghorn chickens as influenced by dietary vitamin E and route of sheep red blood cell administration

Influences of dietary levels of vitamin E fed to hens and their progeny, and routes of SRBC inoculation on antibody responses of diverse populations of chickens were studied. Populations were a commercial broiler sire line (C), 2 commercial broiler dam lines (A and B), and Leghorn lines selected for high (H) or low (L) antibody response to SRBC. Dams from lines A and B were fed diets supplemented with either 10 or 300 IU/kg of vitamin E, whereas dams from lines H and L received only the diet with 10 IU of vitamin E/kg. Progeny from matings of C males with A and B females as well as H and L females mated to males from their respective lines were hatched on the same day and fed diets supplemented with either 10 or 300 IU/kg of vitamin E. Breeders were the same age and eggs were incubated in the same machine. Chicks were inoculated on d 14 intravenously with 0.1 mL of a 0.5% suspension of SRBC or intramuscularly with 0.1 mL of a 25% suspension of SRBC. Antibody response was measured 6 and 14 d later. Chicks received a booster i.m. inoculation of 0.1 mL of 25% SRBC on d 28. Titers were again measured 6 and 14 d later. Level of vitamin E fed to dams did not affect progeny BW or plasma vitamin E levels. Although titers were higher following i.v. than i.m. inoculation, the degree of difference varied among stocks. Dietary vitamin E level interacted with inoculation route with a greater response to the higher than lower level of vitamin E for i.v., but there was no difference for i.m. There were stock x level of vitamin E and stock x route of inoculation interactions for secondary responses to SRBC inoculation. Stock rankings after the first inoculation were not predictive of the rankings after the second inoculation. The 30-fold increase in dietary level of vitamin E resulted in >12-fold differences in plasma levels of vitamin E. Overall, there was a stock-dependent influence of dietary vitamin E on growth and humoral antibody response.

Stress response differences and disease susceptibility reflected by heterophil to lymphocyte ratio in turkeys selected for increased body weight

Three genetic lines of turkeys were compared for their responses to Escherichia coli challenge following dexamethasone injection (Dex) or E. coli challenge preceding transport stress (TS). The turkey lines were a slow growing line selected for increased egg production (Egg line), a fast growing line selected for increased 16-wk BW (F line), and a commercial line (Comm line). At 14 wk of age, the Dex group was treated with 3 injections of 2 mg of Dex/kg of BW followed by airsac challenge with 100 cfu of E. coli. The TS group was given the same E. coli challenge at 1 x 10(4) cfu/bird without Dex treatment, and was subjected to transport stress, including 12 h of holding time in a transport vehicle, 8 d after the challenge. All treated birds and untreated control birds were bled at the same time, which was 1 d after transport and 9 d after challenge with E. coli. The main effect mean (MEM) total leukocyte counts (WBC) and the percentages of eosinophils (Eos) and basophils (Baso) were the same for all 3 lines; however, the MEM percentages of heterophils (Het) and monocytes (Mono) and the heterophil/lymphocyte ratio (H/L) were lower and the percentage of lymphocytes (Lym) was higher in the Egg line compared with the 2 fast-growing lines. Both stress treatments increased WBC, Het, and H/L and decreased Lym in all 3 lines; however, these effects were significantly greater in both fast growing lines compared with the Egg line. Sixteen-week BW was unaffected by either treatment in the Egg line and was decreased by both treatments in the Comm line and by the Dex treatment in the F line. Main effect mean airsacculitis score (AS) was not affected by line and was significantly increased by TS and Dex treatments. Neither treatment affected AS of the Egg line birds, whereas Dex treatment increased AS of the F line, and both Dex and TS increased AS of the Comm line. Mortality was significantly higher in the Comm line compared with the Egg line and was intermediate in the F line. The differences between these lines in their disease resistance and physiological response to stress in 2 stress models suggests that increasing selection for BW of turkeys is accompanied by changes in the stress response resulting in increased susceptibility to opportunistic bacterial infection.

Recent progress on the cytokine regulation of intestinal immune responses to Eimeria

A variety of methods are available to combat avian diseases in the commercial setting, including improved farm management practices, use of antibiotic drugs, selection of disease resistant chicken strains, and manipulation of the chicken immune system. In the latter category, development of vaccines against the major avian diseases has become a priority for the poultry industry. With increasing demands for developing alternative control programs for many poultry diseases, it is important to understand the basic immunobiology of host-pathogen interactions in order to develop novel vaccination strategies. From studies carried out in many mammalian species, it is evident that host immune responses to intracellular pathogens are complex and involve many components of the host immune system. For enteric pathogens such as Eimeria and Salmonella, understanding cell-mediated immunity is most important because antibodies, although abundantly produced locally, can not access and act on these intracellular pathogens. In poultry, slow but increasing understanding of various components of host immune system mediating cellular immunity is opening new opportunities for thorough investigation of the role of thymus-derived lymphocyte subpopulations and cytokines in normal and disease states. This paper will review recent progress with chicken cytokines that have been characterized, and discuss various experimental strategies to enhance host immunity to pathogens using chicken cytokines.

Immune function across generations: integrating mechanism and evolutionary process in maternal antibody transmission

The past 30 years of immunological research have revealed much about the proximate mechanisms of maternal antibody transmission and utilization, but have not adequately addressed how these issues are related to evolutionary and ecological theory. Much remains to be learned about individual differences within a species in maternal antibody transmission as well as differences among species in transmission or utilization of antibodies. Similarly, maternal-effects theory has generally neglected the mechanisms by which mothers influence offspring phenotype. Although the environmental cues that generate maternal effects and the consequent effects for offspring phenotype are often well characterized, the intermediary physiological and developmental steps through which the maternal effect is transmitted are generally unknown. Integration of the proximate mechanisms of maternal antibody transmission with evolutionary theory on maternal effects affords an important opportunity to unite mechanism and process by focusing on the links between genetics, environment and physiology, with the ultimate goal of explaining differences among individuals and species in the transfer of immune function from one generation to the next.

Genetic markers associated with antibody response kinetics in adult chickens

A linkage disequilibrium approach with microsatellites was employed to investigate QTL affecting immune response. Highly inbred males of two MHC-congenic Fayoumi chicken lines were mated with highly inbred G-B1 Leghorn hens. Adult F2 hens (n = 158) were injected twice with SRBC and fixed Brucella abortus (BA). Agglutinating antibody titers were measured. Secondary phase parameters of maximum titers (Ymax) and time (Tmax) needed to achieve Ymax were estimated from postsecondary titers by using a nonlinear regression model. A three-step genotype strategy (DNA pooling, selective genotyping, and whole population genotyping) was used to identify microsatellite markers that are associated with immune response to SRBC and BA. The linkage distances between adjacent markers in the F2 population were estimated by Crimap. The QTL affecting immune response to SRBC and BA were detected based on F statistic by interval mapping. A total of five significant QTL, as determined by a permutation test, were detected at the 5% chromosome-wise level on Chromosomes 3, 5, 6, and Z. Two (Chromosome 3 and 6) of five QTL were significant at the 1% chromosome-wise level. The variance explained by the QTL ranged from 6.46 to 7.50%. The results suggest that regions on Chromosomes 3, 5, 6, and Z contain QTL that affect antibody kinetics in the hen.

Immunocontraception for population control: will resistance evolve?

The prospect for successful biocontrol using immunocontraception is threatened if there is adaptation to the vaccine through natural selection of individuals that are genetically resistant to the contraceptive agent. To assess this possibility we examined the literature and found that little relevant data are available for any species on the appropriate trait, fertility variation among immunized individuals, or about appropriate population and genetic parameters influencing the likelihood of a selection response. Some data are available on variation in antibody response to immunocontraceptives, but the relationship between antibody response and fertility levels is poorly documented. The antibody response data indicate low heritability for this trait suggesting that fertility levels of contraceptive-resistant individuals will also have a low heritability. Slow evolution of contraception resistance might therefore be anticipated. The absence of information about relevant parameters makes the construction of quantitative models premature. We discuss factors in particular need of investigation if predictions about resistance evolution are to be made. These include: 1. the genetic basis of fertility retention, 2. the proportion of the population resistant to the contraceptive agent and how this is affected by gene flow from refuge populations, 3. the genetically-based fitness tradeoffs of resistant individuals that often accompany selection, 4. cross-generation effects that can thwart the effects of selection, and 5. the efficiency of delivery of the contraceptive agent. An understanding of the above for particular species, and the development of appropriate divergently acting multiple vaccines that can be used in temporal rotation or in mixtures, should facilitate the development of management options to minimize resistance evolution.

Chicken quantitative trait loci for growth and body composition associated with transforming growth factor-beta genes

Transforming growth factor-beta (TGF-beta) belongs to a large family of multifunctional growth factors that regulate a broad spectrum of biological activities involved in morphogenesis, development, and differentiation. The current study was designed to investigate the effects of TGF-beta genes on chicken growth and body composition traits. The Iowa Growth and Composition Resource Population was established by crossing broiler sires with dams from two unrelated highly inbred lines (Leghorn and Fayoumi). The F1 birds were intercrossed, within dam line, to produce two related F2 populations. Body weight and body composition traits were measured in the F2 population. Primers for TGF-beta2, TGF-beta3, and TGF-beta4 were designed from database chicken sequence. Polymorphisms between parental lines were detected by DNA sequencing, and PCR-RFLP methods were then developed to screen the F2 population. The TGF-beta2 polymorphisms between broiler and Leghorn and the TGF-beta4 polymorphism between broiler and Fayoumi were associated with traits of skeletal integrity, such as tibia length, bone mineral content, bone mineral density, and the percentage of each measure to BW. The TGF-beta3 polymorphism between broilers and Leghorns was associated with traits of growth and body composition, such as BW, average daily gain, weight of breast muscle, abdominal fat pad and spleen, as well as the percentage of these organ weights to BW, and the percentage of shank weight and length to BW. The current research supports the broad effects of TGF-beta genes on growth and development of chickens.

Effects of genetic selection for high or low antibody response on resistance to a variety of disease challenges and the relationship of resource allocation

Lines of white leghorn chickens were selectively bred for either a high (H) or low (L) antibody response to sheep erythrocytes. The parental lines, HH and LL, and reciprocal crosses, HL (sire line cited first and dam line second) and LH, were compared for their responses to various diseases. High antibody titers were associated with reduced body weight. Lines and their crosses were challenged with infectious diseases. The LL line was most resistant to Mycobacterium avium, whereas the HH line was most susceptible. The HH line was most resistant to Mycoplasma gallisepticum, whereas the LL line was most susceptible. These findings indicate that defense against infectious diseases are resource expensive. In order to save resources, it is possible that different parts of a population might genetically devote high levels of resources against different types of diseases so that the entire population is not susceptible to a single infection.