Leghorn Lines Research Articles

Assessing Genetic Diversity and Population Structure for Commercial Chicken Lines Based on Forty Microsatellite Analyses

The aims of the current study were to assess genetic diversity, conduct genetic characterization, and evaluate usefulness of an individual assignment test for 12 commercial chicken lines using 40 microsatellite markers. A total of 268 distinct alleles were observed across the 12 lines, and 42 of the 268 alleles (15.7%) were unique to only 1 line. Mean observed heterozygosity within a line ranged from 0.295 to 0.664, and the highest value was obtained from 1 of the White Plymouth Rock lines. Significant deviations from the Hardy-Weinberg equilibrium were observed at several locus-line combinations, showing excess of heterozygotes in many cases. As a whole, genetic differences among the lines estimated by the fixation index were high at 29.8%, whereas higher genetic similarity was observed among White Leghorn lines despite their different breeding histories. Assignment test could correctly allocate individuals at the line level to their origins, with a high accuracy (96.6%). Individual-based genetic characterization would be a usable step to conserve chicken genetic resources. Here, guidelines for future breeding and management of these lines by the poultry industry are provided.

New alleles of chicken CD8α and CD3d found in Chinese native and western breeds

Chinese native chicken breeds provide useful resources for the study of genetic diversity. In this study, the alleles of CD8α and CD3d cDNA from Chinese native and introduced western breeds of chicken were analyzed at the sequence level. Six alleles were found, due to 13 amino acid replacements in the extracellular domain of the CD8α sequence. There were four alleles detected in the Chinese strains, and alleles 5 and 6 were identified for the first time. Allele 6 was shared by Langshan, Beijing Fatty and Recessive White Feather chickens. Allele 2, found in the Bigbone strain, was the same as that found in the Leghorn strain H.B15.H7, and allele 3 in the Xianju breed was also the same as in the Leghorn strain H.B15.H12. Two Leghorn lines (RPL line 7 and AY519197) and the Camellia possessed an allele (alleles 1, 4 and 5), respectively, that was not found in the other lines. Nine out of 13 amino acid replacements were situated in the putative major histocompatibility complex (MHC) class I binding CDR1 (positions 30, 33 and 34), CDR2 (positions 58, 62, 63 and 65) and CDR3 (positions 90 and 106). Except for the Xianju breed, the CD8α cDNA of Chinese native chicken breeds shared high homology. Two alleles were found in CD3d. Three additional nucleotides were found at positions 64, 65 and 66 in the newly discovered allele 2. This led to a difference of four amino acids (at residues 22, 23, 24 and 25) in the extracellular domain of CD3d cDNA from the Gushi, Recessive White Feather and ISA chickens compared with these of the White Leghorn and T11.15 ( NM_205512). Five hybridoma clones (1C9, 1H5, 4B11, 6G5 and 13C5) against chicken CD8α were generated by DNA immunization. Two monoclonal antibodies (mAbs), 6G5 and 4B11, showed reactivity to the splenocytes from five Chinese native chicken breeds, the Recessive White Feather chicken and the Leghorn ( AY519197), while mAbs 1C9, 1H5 and 13C5 showed no reaction with these breeds.

Antibody Responses to Keyhole Limpet Hemocyanin, Lipopolysaccharide, and Newcastle Disease Virus Vaccine in F2 and Backcrosses of White Leghorn Lines Selected for Two Different Immune Response Traits

Planned crosses were designed to produce an F(2) and 2 backcross populations from 2 lines of White Leghorn chickens previously selected over 10 generations for 2 different in vivo immune responses. The selection criteria applied on the 2 grandparental lines were as follows: high antibody response to Newcastle disease virus vaccine 3 wk after vaccination (ND3) and high cell-mediated immune response [response to phytohemagglutinin]. Furthermore a control line was kept by random breeding. The objective of the study was to estimate if the 2 selection criteria applied on the pure lines had changed the level of and type of immune (humoral) response to a new antigen, keyhole limpet hemocyanin (KLH), in the various second-generation progeny groups. In addition, correlations between parameters of acquired and innate immunity were tested. Primary total (IgT) and isotype-specific (IgG and IgM) antibody response to KLH 1 wk after immunization and levels of natural antibodies (NAB) binding to Salmonella enteriditis-derived lipopolysaccharide (LPS) were measured. Although no differences were present between IgM and IgG antibodies to KLH and the phytohemagglutinin skin-swelling response, significant differences were present between all the progeny groups for IgT to KLH and ND3 and NAB binding to LPS. The mean values for IgT to ND3 and KLH were significantly different between the crosses using the selected lines compared with the control line, indicating a contribution of the previous selection. In addition, a sex effect was found for IgM to KLH and NAB to LPS, for which females had a higher response than males in both cases. No interaction between progeny type and sex was found. Furthermore, significant positive correlations were found between NAB to LPS and specific antibody titers to KLH. Finally, the results of the present study demonstrated an interaction between innate and acquired immunity under this strategy of selection and crossbreeding and confirmed the effect of selection on general immune response to a new antigen in second-generation crosses.

Chicken Gallinacin Gene Cluster Associated with Salmonella Response in Advanced Intercross Line

Salmonella enterica serovar Enteritidis is a gram-negative bacterium that negatively affects human and animal health. Many eukaryotes use antimicrobial peptides (alpha-defensins, beta-defensins, gamma-defensins, and cathelicidins) in innate immune responses to fight bacterial infections. Poultry gallinacins are the functional equivalents of mammalian beta-defensins. Two related advanced intercross lines of chickens were analyzed for association of gallinacin genotypic variation with Salmonella Enteritidis burden levels in the cecum and spleen after infection. Thirteen genes of the chicken beta-defensin cluster (GAL1-13) were sequenced from individuals of each advanced intercross line, plus the founder broiler sire and representatives of the highly inbred Leghorn and Fayoumi founder dam lines. The mean was 17 single-nucleotide polymorphisms (SNPs) per kilobase. One single-nucleotide polymorphism per gene was genotyped with SNaPshot to test for statistical associations with Salmonella Enteritidis colonization after challenge. Among the 13 gallinacin genes evaluated, the single-nucleotide polymorphisms in all genes in a cluster of three adjacent genes (GAL11, GAL12, and GAL13) were associated with bacterial load in the cecal content in the broiler x Leghorn advanced intercross line (three-gene SNP genotype effect, P < 0.008). The results strongly suggest a role of the gallinacins in defense of poultry against enteric pathogens. The use of gallinacin single-nucleotide polymorphisms as molecular markers for genetic selection for Salmonella Enteritidis resistance might result in reduced bacterial burden via development of an enhanced innate immune response.

The novel object test as predictor of feather damage in cage-housed Rhode Island Red and White Leghorn laying hens

The propensity to develop feather pecking (FP) has a genetic component and has been related to fear responses in laying hens. A convenient test measuring the fear response might therefore be used to identify hens with a stronger propensity to develop FP. However, genetic origin and age can influence the relation between fear response and FP. The present study investigated the use of a novel object test in the home cage as predictor of FP in six lines of laying hens from Rhode Island Red origin and six lines from White Leghorn origin at adult age. Incidence of FP was assessed by scoring feather damage at back, rump and belly at 35, 43, 51, 63 and 69 weeks of age. A novel object test, measuring fear response to a rod, was performed at 23, 46 and 69 weeks of age. For RIR lines, a stronger fear response at 23 weeks was related to decreased feather damage at 51 weeks and for both RIR and WL lines stronger fear responses at 46 weeks were related to increased feather damage at 51 weeks. These results suggest that the relation between FP and fear response differs between ages and between Rhode Island Red and White Leghorn lines.

Pure line laying chickens at the Agassiz Research Centre

SummarySix lines of laying chickens representing high-producing non-industrial lines chosen or produced with consideration for characters of production are being kept at the Agassiz Research Centre. The collection includes one Barred Plymouth Rock (Line 60), one Columbian Plymouth Rock, one Rhode Island Red (Line 50), and three White Leghorn lines (Blue, Black, and Burgundy). Before coming to the Agassiz Research Centre these pure lines were subjected to mild selection for egg production and their egg production approaches that of commercial hybrids. The lines are currently maintained as a genetic resource as live populations without selection and with populations large enough to minimize inbreeding. In addition, samples of DNA from these lines have been conserved for genetic studies, and samples of embryonic cells are being kept cryogenically to allow the possibility of reconstitution of the lines through the production of germline chimeras. Techniques of ovarian transplantation are being developed which will allow more efficient cryogenic conservation and recuperation of the genetic material into live populations.

Effect of strain of layer and age at photostimulation on egg production, egg quality, and bone strength

Bone strength in layers is a concern for economic reasons and animal welfare concerns. Bone characteristics were investigated in 3 strains of hens: Babcock B-300, a small-bodied commercial white-egg layer; ISA-Brown, a commercial brown-egg layer; and an unselected Brown Leghorn line (BL). After being reared together in a single pen with 8 h of light per day, hens were caged with 14 h of light per day. Half of the hens were caged at 18 wk of age and the other half at 20 wk of age, resulting in a 2-wk difference in the age at photostimulation. Body weights, egg production, feed efficiency, and egg quality were measured throughout production. At 15, 25, 50, and 74 wk of age, hens were euthanized for sampling of the radius and the humerus. Breaking strength of the radius and humerus was measured, and the area and density of trabecular (largely medullary bone) and cortical bone were measured using quantitative computed tomography. Egg production and feed conversion of ISA-Brown hens was as good as or better than that of Babcock B-300 hens, and both commercial strains had higher production than the BL. Photostimulation late delayed sexual maturity and improved albumen and shell characteristics but had only minor effects on egg production and did not affect the yolk weight. The delayed photostimulation resulting from caging 2 wk later affected the radius by increasing the area of the trabecular space at 50 wk of age and the density of the bone in the trabecular space at 74 wk of age. Breaking strength of the humerus at 25 wk of age was greater for the birds that were photostimulated late but was not different later in the trial. The humerus, but not the radius, of the BL had a greater breaking strength than that of the commercial strains, suggesting that selection has decreased humeral breaking strength.

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 × level of vitamin E and stock × 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.

Development of Immunofluorescence-Based Virus Neutralization Test for the Detection of Antibodies to Chicken Anemia Virus

ABSTRACTA novel immunoflorescence-virus neutralization microtest (VNIF), based on the immuno-fluorescent detection of virus antigens in cells, inoculated with virus/antibody mixtures was developed for determination of neutralizing antibodies against chicken anemia virus (CAV). For this purpose serial dilutions of tested sera were incubated with 105 TCID50 of Del Rose strain of CAV and neutralizing mixtures incubated with MDCC-MSB1 cells in 96-well microtest plates. The infected cell cultures were subpassaged once, and 48h thereafter tested for the presence of residual virus in neutralizing mixtures using direct immunofluorescent test (IF). Two sera from Leghorn line 15 I hens, reared at separated conditions and vaccinated with commercial vaccine CAV P4, four other sera from chickens from the same line and 5 serum samples from commercial broiler chickens were tested comparatively by both virus neutralization (VN) and VNIF tests. The sensitivity of VNIF was shown to be greater than a conventional VN test, which rely on subjective recognition of cytopathic effect (CPE), and viral activity was detected in wells, inoculated with endpoint dilutions of virus-serum mixture and judged as CPE-negative. The VNIF system have the advantages to be more objective and rapid than the classical VN and could successfully be used for large-scale serological monitoring of CAV infection.

Comparison of chicken genotypes: myofiber number in pectoralis muscle and myostatin ontogeny

This study was performed to evaluate breast muscle development in chicken genotypes divergently selected for muscularity. In the first experiment, 2 commercial broiler lines (a high breast yield, HBY, and a normal breast yield broiler strain-cross, NBY) and a Leghorn line were grown up to 35 d to evaluate BW, breast weight, and breast yield. At 7 and 21 d of age, pectoralis muscle was used to estimate myofiber density (MFD, number of myofibers per mm2) and total apparent myofiber number (MFN). In the second experiment, the ontogeny of myostatin was determined from broiler- and Leghorn-type chick embryos, at embryonic days 1 to 20 (E1 to E20), using reverse transcription (RT)-PCR. As expected, the Leghorn line had lower BW, breast weight, and breast yield than broiler lines. The HBY line showed higher breast yield at all ages evaluated, but lower BW at 21 and 35 d than the NBY line. The Leghorn line had 45% higher MFD than broilers, which indicates an increased cross-sectional area of the myofibers in broiler lines. No MFD difference was observed between the broiler strains (P > 0.05). The myofiber number of broilers was more than twice that of Leghorns and HBY had 10% higher MFN than the NBY line. Myofiber number was correlated to BW (r = 0.58), breast weight (r = 0.58), and breast yield (r = 0.69). Conversely, MFD showed negative correlation with BW, breast weight, and breast yield (r = -0.85, -0.83, and -0.88, respectively). No effect of genotype or interaction between genotype and embryonic age was observed for myostatin expression. This study showed that broilers have higher MFN in the breast muscles than Leghorn-type chickens, and that high breast yield of broiler strains may be due to increased MFN. Higher muscularity of broilers, as compared with Leghorns, was not attributed to lower expression of myostatin during embryonic development.

Genetic Line Effect on Peripheral Blood Leukocyte Cell Surface Marker Expression in Chickens

To determine the role of genetics in baseline lymphocyte parameters, several distinct lines of chickens were examined for differences in peripheral blood leukocyte (PBL) populations. Four highly inbred chicken lines (MHC congenic Fayoumi lines M15.2 and M5.1, and MHC congenic Leghorn lines G-B1 and G-B2), two advanced intercrosses [F5 (Broiler × G-B2) and F5 (Broiler × M15.2)], and an outbred population of broilers were used. Leukocytes isolated from healthy adult birds were labeled with monoclonal antibodies: chCD3, chCD4, chCD8, chBu-1, and hCD14. Flow cytometry was used to determine the total percentage of positively labeled cells for each surface marker in a sample, as well as the mean fluorescent intensity, or surface marker density, of a labeled subset. Significant line differences for percentage positive CD3 T cells and the ratio of B cells:T cells (represented by the Bu-1:CD3 ratio) were found. The effect of line was also significant for CD3 and CD8 T cell receptor density. Effects of sex and MHC on PBL cell surface marker expression were not significant in the lines examined. This study demonstrates the effect of genetic line on resting leukocyte composition of peripheral blood in the chicken lines examined. Observed PBL differences add to our growing knowledge of the varied roles that immune system status (defined by specific cell populations) and genetic background have in determining susceptibility and disease progression in chickens.

Serum haemolytic complement activities in 11 different MHC (B) typed chicken lines.

To study the relation between serum complement levels and the chicken MHC (B) complex, complement haemolytic activity was measured in sera from hens from seven pure-bred B-typed White and one Brown Leghorn lines, and three ISA-Warren lines that had been divergently selected for antibody responses to sheep red blood cells (SRBC). Significant differences occurred in the serum haemolytic complement activities, both belonging to the classic (CPW) and the alternative (APW) pathways, among the 11 different haplotyped chicken lines. Hens with high CPW and high APW titres predominantly displayed the B2 or B21 haplotypes. Chickens with low CPW and APW were found in B14 and B15 haplotypes. Haplotype B14 appears to be different in complement levels when present into the pure-bred lines or into the ISA-Warren line selected for low antibody responses to SRBC. Otherwise, the presence of B21 in ISA-Warren line selected for high antibody responses to SRBC does not differ with the B21 in the inbred lines (except in the NL-line for CPW values). In general the haplotypes B2 and B21 are found in chicken lines with enhanced disease resistance, and the B15 haplotype has been connected with enhanced disease susceptibility. Our results suggest that levels of haemolytic complement activity, either from the classical or from the alternative pathways, may underlie part of the immunocompetence ascribed to the MHC (B) complex in chickens.

Distinctive polymorphism of chicken B-FI (major histocompatibility complex class I) molecules

The major histocompatibility complex (MHC) in chickens influences disease resistance, but the mechanism is not understood. In Leghorn lines, the MHC contains 2 closely-linked class I loci, B-FI and B-FIV. Previously, we determined nucleotide sequences of well-expressed class I (B-F) genes from unique MHC haplotypes of broiler chicken lines. More recently, we identified 7 new B-F α1α2-coding sequences from less well-expressed loci by amplification of genomic DNA from unique broiler haplotypes. Phylogenetic analysis of chicken MHC class I α1α2-coding sequences resolved 2 clusters (Groups A and B), which appear to correspond to B-FIV and B-FI loci, respectively. Compared with B-FIV locus, B-FI alleles were less polymorphic overall, but nevertheless demonstrated evidence of diversifying selection. The most striking feature of B-FI alleles is a conserved, locus-specific motif in the α helix of the α1 domain, a region that is highly variable in B-FIV alleles. This distinctive pattern of allelic polymorphism resembles that of the HLA-C class I locus in the human MHC (HLA). The conservation of the α helix of the α1 domain relates to HLA-C interaction with members of the killer immunoglobulin-like receptors on natural killer (NK) cells that are specific for recognition of HLA-C molecules and function to regulate activation of NK cells. Whereas HLA-C molecules may be dominant ligands for NK cell regulation, HLA-A and -B molecules are more important in presenting antigen to cytotoxic T lymphocytes. We hypothesize that chicken B-FI molecules may be specialized to serve similar functions as HLA-C molecules.

Chicken MHC class I and II gene effects on antibody response kinetics in adult chickens.

The major histocompatibility complex (MHC) plays an important role in regulation of the immune response. The MHC class I and II genes were selected as candidates to investigate associations with vaccine response to Salmonella enteritidis and kinetics of antibody response to sheep red blood cell (SRBC) and Brucella abortus. Primary antibody response after S. enteritidis vaccination at day 10, and antibody response to SRBC and killed B. abortus after immunization at 19 and 22 weeks were measured in an F2 population. The resource population was derived from males of two highly inbred MHC-congenic Fayoumi chicken lines (M5.1 and M15.2) mated with highly inbred G-B1 Leghorn line hens. Secondary phase parameters of minimum titers ( Y(min)), maximum titers ( Y(max)), and time needed to achieve Y(min) ( t(min)) and Y(max) ( t(max)) were estimated from post-secondary titers by using a non-linear regression model. Associations of single nucleotide polymorphisms (SNPs) in MHC class I and II genes with antibody response parameters were determined by a general linear model. Significant associations were found primarily in the M15.2 grandsire haplotype. There were significant associations between MHC class I alpha(1) and alpha(2) SNPs and antibody response to S. enteritidis, primary antibody response to B. abortus, Y(min) to SRBC, and Y(max) to both SRBC and B. abortus. There were significant effects of the MHC class II beta(1) domain SNP on S. enteritidis antibody and Y(max) to SRBC. The results suggest that the characterized SNPs might be used in future applications by marker-assisted selection to improve vaccine response and immunocompetence in chickens.

Candidate Gene Approach: Potentional Association of Caspase‐1, Inhibitor of Apoptosis Protein‐1, and Prosaposin Gene Polymorphisms with Response to Salmonella enteritidis Challenge or Vaccination in Young Chicks#

Salmonella enteritidis (SE) contamination of poultry products is a major cause of food‐borne disease worldwide. Caspase‐1 and inhibitor of apoptosis protein‐1 (IAP‐1) were selected as candidate genes for chicken response to SE because their proteins play critical roles in the apoptotic pathway when intracellular bacteria interact with host cells. Prosaposin (PSAP) was selected as a positional candidate gene based on a previous quantitative trait loci (QTL) linkage study using the same population. The F1 offspring of outbred sires crossed with three diverse, highly inbred dam lines (two major histocompatibility complex‐congenic Leghorn lines named G‐B1 and G‐B2, and one Fayoumi line) were used to define the phenotypes. The F1 birds were involved in either pathogenic SE challenge, in which spleen and cecum content bacterial load were quantified, or SE vaccination, in which plasma antibody level to SE vaccine was evaluated. A polymerase chain reaction‐restriction fragment length polymorphisms (PCR‐RFLP) assay was developed to identify single‐nucleotide polymorphism (SNP) in the three genes. The F1 offspring of heterozygous sires for each gene were genotyped. The sire caspase‐1 gene was significantly associated with cecum content bacterial load (P = 0.04) in the three combined dam line crosses, and with spleen bacterial load in the G‐B1 cross (P = 0.02). The sire caspase‐1 gene was also significantly associated with antibody level to SE vaccine (P = 0.03) in F1 males in the three combined dam line crosses. The sire IAP‐1 gene was significantly associated with spleen bacterial load (P = 0.04) in the three combined dam‐line crosses, and interacted with dam‐line genetics (P = 0.01) for cecum content bacterial load. The sire PSAP gene significantly interacted with sex for spleen bacterial load (P = 0.004). This study is the first to demonstrate the association of SNPs for caspase‐1, IAP‐1, and PSAP genes with SE vaccine and with pathogen challenge response in chickens. #Journal paper No. 19835 of the Iowa Agriculture and Home Economics Experiment Station, Ames, IA 50011; Projects 2237 and 3521.

Genetic relations of yolk proportion and chick weight with production traits in a White Leghorn line

1. The main purpose of this study was to estimate genetic correlations between yolk proportion, chick weight and production traits using an animal model. 2. Direct-direct genetic correlations were estimated between yolk proportion and age at first egg (−0·34), body weight at 20 (0·10), 40 (0·58) and 60 (0·52) weeks of age, egg number (0·56), egg mass (0·59), feed intake (0·64) and feed conversion (−0·25). 3. Maternal-direct genetic correlations were estimated between chick weight and age at first egg (0·40), body weight at 20 (0·57), 40 (0·66) and 60 (0·56) weeks of age, egg number (−0·50), egg mass (0·21), feed intake (0·45) and feed conversion (0·17), respectively. 4. In conclusion, the results suggest that selection on a higher yolk proportion would not have any unfavourable effects on egg production. Maternal-direct genetic correlations between chick weight and production traits resembled direct-direct genetic correlations between egg weight and production traits found in other studies.

Genetic relations of yolk proportion and chick weight with production traits in a White Leghorn line

Genetic relations of yolk proportion and chick weight with production traits in a White Leghorn line

Genetic correlations between the maternal genetic effect on chick weight and the direct genetic effects on egg composition traits in a White Leghorn line

Selection can be a useful way to alter yolk proportion and thereby egg dry matter which, owing to its economic importance, is a trait of substantial importance for the egg-processing industry. However, the egg is primarily the chamber of embryonic development. The main purpose of this study was to estimate genetic correlations between the maternal effect on chick weight at hatching and the direct effect on different egg composition traits, in particular, yolk proportion. Additionally, genetic parameters were estimated for egg composition traits. To create a data set suitable for estimation of genetic parameters, a three-round selection experiment was set up. Birds were selected based on their predicted breeding values for the genetic maternal effect on chick weight and the direct genetic effect on yolk proportion according to the theory of elliptical selection. Genetic parameters were estimated using a multiple trait animal model and restricted maximum likelihood. The maternal heritability for chick weight was 0.5, whereas the direct heritability was dose to 0. The genetic correlations between the maternal effect on chick weight and the direct effect on yolk proportion, yolk weight, albumen weight, albumen dry matter concentration, and egg weight were 0.14, 0.76, 0.93, 0.14, and 0.99, respectively. The heritabilities for yolk proportion, yolk weight, albumen weight, albumen dry matter concentration, and egg weight were 0.33, 0.43, 0.57, 0.38, and 0.60, respectively. We conclude that breeding ought to be a useful way to increase egg dry matter with no expected unfavorable correlated effects on chick weight.

Alloantigen System L Affects Antibody Responses

Alloantigen system L is a polymorphic protein expressed on the surface of chicken erythrocytes and possibly certain leukocyte subpopulations. Previous studies demonstrated that the L system affects Rous sarcoma outcome and phagocytic function. The present experiments examined the L system influence on antibod y responses to two antigens: SRBC (T-dependent) and Brucella abortus (BA, partially T-independent) in three B complex genotypes. The parental stock were 50% Modified Wisconsin Line 3 x White Leghorn Line NIU 4 and 50% Inbred Line 6-15.5. Pedigree matings of 4 B B L L sires to 5 B B L L dams per sire produced three 2 5 1 2 2 5 1 2 hatches (n = 183) for the antibody response to SRBC and two hatches (n = 198) to study antibody response to BA. At 4 and 11 weeks of age the experimental birds were injected intravenously with 1 mL of 2.5% SRBC or 0.1 mL of 10% BA. Total and mercaptoethanol (ME)-resistant primary and secondary titers were analyzed by least squares ANOVA. Alloantigen L had a significant effect on total primary antibody titer to SRBC in a B B background (p < 0.004) and on total (p < 0.011) and ME-resistant (p < 0.017) secondary titer to SRBC 5 5 in the B B genotype. Total (p < 0.004) and ME-resistant (p < 0.005) secondary titers to BA in B B chickens 2 5 2 5 were significantly affected by alloantigen L. The data indicate that the alloantigen L locus or genes in the immediate chromosomal vicinity affect antibody responses to SRBC and BA.

Mapping of quantitative trait loci for body weight at three, six, and nine weeks of age in a broiler layer cross

An F2 chicken population was established from a cross of a broiler sire-line and an egg laying (White Leghorn) line. There were two males and two females from both lines in the base population. The F1 progeny consisted of 8 males and 32 females. Over 500 F2 offspring from five hatches were reared to slaughter at a live weight of 2 kg at 9 wk of age. Body weights at 3, 6, and 9 wk were recorded. The DNA was extracted from blood samples, and genotypes for 101 microsatellite markers were determined. Data of 466 individuals from 30 families were available for analysis. Interval mapping QTL analyses were carried out. The QTL significant at the genome wide level that affected body weight at two ages were identified on chromosomes 1, 2, 4, 7, and 8 and a QTL on Chromosome 13 influenced body weight at all three ages. Genetic effects were generally additive, and the broiler allele increased body weight in all cases. The effects for significant individual QTL accounted for between 0.2 and 1.0 phenotypic standard deviations and the sum of the additive effects accounted for approximately 0.75 of the line difference in body weight at 6 wk of age. The largest single additive effect was on chromosome 4, and the effect of substituting one copy of the gene was an increase in weight of 249 g. Interactions of the QTL with sex or family were unimportant. There was no evidence for imprinting or of two or more QTL at the same location for any of the traits.