Corticosterone in feathers of laying hens: an assay validation for evidence-based assessment of animal welfare

Studies indicate that the evaluation of animal welfare in birds may be carried out with the measurement of the stress-related hormone corticosterone in feathers. However a standardized procedure for corticosterone measurements in feathers is lacking, a validation needs to be carried out for each new species before implementation. The aim of the present study was to establish a valid method to measure corticosterone concentrations in feathers of laying hens in a precise and repeatable manner using an established and commercially available ELISA. Validation was performed with feather pools of tail and interscapular feathers of commercial Lohmann Brown laying hens. Assessment groups, consisting of 5 replicates, were created. All replicates of an assessment group were processed at the same time. Each replicate was run in 4 repetitions by ELISA. Intra-assay and interassay CV was 7.5 and 6.4%, respectively. The serial dilution showed linearity and parallelism. Examining the hormone extraction efficiency by using different methanol volumes resulted in no statistical differences (P > 0.05). Pulverized feathers showed higher corticosterone values than minced feathers (P > 0.05). Differences were shown between 2 feather types (tail vs. interscapular feathers; P < 0.05), as well as between vane and rachis (P < 0.05). Performance of a freeze-thaw cycle led to a decrease of corticosterone concentrations in the samples. A possible effect of UV-A radiation on the stability of corticosterone in the feathers was not found (P > 0.05). With the present study, a valid protocol, feasible for analyzing feather pools of laying hens, was developed. It may provide fundamentals for further investigations on corticosterone in feathers as a noninvasive indicator to evaluate aspects of animal welfare.

Genetic approach to select against embryo mortality caused by Enterococcus faecalis infection in laying hens

Selection to reduce susceptibility to Enterococcus faecalis infection in laying hens may contribute to the prevention of amyloid arthropathy since it is mainly induced by this bacterium. Therefore, the aim of the present study was to investigate the possibility to select more laying hens that are resistant against E. faecalis infection through the embryo lethality assay (ELA), which is proposed as an alternative model to replace the adult avian challenge assay. Ten-day-old embryos of 500 Lohmann Brown layers were inoculated into the allantoic cavity with an infectious dose of 2.5 colony-forming units (cfu)/mL of the avian E. faecalis strain K923/96 in 3 ELAs. The embryonic mortality rate (EMR) was determined by candling the eggs daily over a period of 4 d. The average EMR estimated during the 3 ELAs was 50% and the highest EMR occurred 3 to 4 d post inoculation. The estimated heritability for embryonic survivability to the infection was h2 = 0.12-0.14, calculated with the logistic and probit link function, respectively, indicating that the selection of more laying hens that are resistant to E. faecalis infection is feasible. A highly negative genetic correlation was estimated between embryonic survivability and laying performance at the peak of lay (rg = -0.22) and at the end of the production (rg = -0.65), as well as with breaking strength (rg = -0.30 to -0.37). A positive correlation was found between egg weight and the embryonic survivability (rg = +0.16), and no genetic correlation was found with body weight and dynamic stiffness. Therefore, although it was demonstrated that it is possible to breed for E. faecalis resistance, special care should be taken to monitor and to take all traits and their genetic correlations into account in order to achieve a balanced genetic progress. Besides, the ELA does not require that the hens are exposed to pathogens thereby saving labor and cost. Therefore, it could be feasible that ELA be implemented in selection programs.

Reducing the interval of a growth QTL on chromosome 4 in laying hens

In our previous research, we identified a QTL with an interval of 3.4 Mb for growth on chicken chromosome (GGA) 4 in an advanced intercross population of an initial cross between the New Hampshire inbred line (NHI) and the White Leghorn inbred line (WL77). In the current study, an association analysis was performed in a population of purebred white layers (WLA) with White Leghorn origin. Genotypic data of 130 SNPs within the previously identified 3.4-Mb region were obtained using a 60K SNP chip. In total, 24 significant SNPs (LOD ≥ 4.44) on GGA4 were detected for daily weigh gain from 8 to 14 weeks and two SNPs (LOD ≥ 4.80) for body weight at 14 weeks. The QTL interval was reduced by 1.9 Mb to an interval of 1.5 Mb (74.6-76.1 Mb) that harbors 15 genes. Furthermore, to identify additional loci for chicken growth, a genome-wide association study (GWAS) was carried out in a WLA population. The GWAS identified an additional QTL on GGA6 for body weight at six weeks (19.8-21.2 Mb). Our findings showed that by using a WLA population we were able to further reduce the QTL confidence interval previously detected using a NHI × WL77 advanced intercross population.

Validated quantitative trait loci for eggshell quality in experimental and commercial laying hens

Compromised eggshell quality causes considerable economic losses for the egg industry. Breeding for improved eggshell quality has been very challenging. Eggshell quality is a trait that would greatly benefit from marker-assisted selection, which would allow the selection of sires for their direct contribution to the trait and would also allow implementation of measurements integrating a number of shell parameters that are difficult to measure. In this study, we selected the most promising autosomal quantitative trait loci (QTL) affecting eggshell quality on chromosomes 2, 3, 6 and 14 from earlier experiments and we extended the F₂ population to include 1599 F₂ females. The study was repeated on two commercial populations: Lohmann Tierzucht Rhode Island Red line (n = 692 females) and a Hy-Line White Plymouth Rock line (n = 290 progeny tested males). We analyzed the selected autosomal QTL regions on the three populations with SNP markers at 4-13 SNPs/Mb density. QTL for eggshell quality were replicated on all studied regions in the F₂ population. New QTL were detected for eggshell color on chromosomes 3 and 6. Marker associations with eggshell quality traits were validated in the tested commercial lines on chromosomes 2, 3 and 6, thus paving the way for marker-assisted selection for improved eggshell quality.

Haematological and febrile response to Escherichia coli lipopolysaccharide in 12-week-old cockerels of genetically diverse layer lines fed diets with increasing L-arginine levels

Due to its decisive function in the avian metabolic, endocrine and immune system L-arginine (Arg) is dietary indispensable for chickens. In 12-week-old cockerels of two high- and two low-performing purebred layer lines, the effects of increasing dietary Arg on the haematological and febrile response were studied over 48 h after single lipopolysaccharide (LPS) injection. The offered diets contained Arg equivalent to 70%, 100% and 200% of recommended supply. Pathophysiological alterations in weight gain, feed intake, body temperature and differential blood count were examined in comparison with their physiological initial values. Within the first 24 h after LPS injection, cockerels reduced feed intake and lost body weight subsequently. Thereby, low-performing genotypes lost body weight to a lesser extent than high-performing ones. The loss of body weight was further intensified by deficient dietary Arg. Within the following 24 h, cockerels recovered by improving feed intake and weight gain. Furthermore, LPS induced genotype-specific fever response: both brown genotypes showed initial hypothermia followed by longer lasting moderate hyperthermia, whereas the white genotypes exhibited biphasic hyperthermia. Fever response was accompanied by significant changes in differential blood counts. Characterized by lymphopenia and heterophilia, a severe leucopenia was observed from 4 to 8 h after LPS injection and replaced by a marked leucocytosis with longer lasting monocytosis up to 48 h after LPS injection. Under given pathophysiological conditions, deficiently Arg-supplied cockerels showed higher total leucocyte counts than adequately and excessively Arg-supplied cockerels. However, deficient and surplus dietary Arg tended to cause higher ratios between heterophils and lymphocytes. To conclude, present results confirmed that LPS induced numerous immunological changes in 12-week-old cockerels and emphasized that chicken's genotype is a source of variation to be considered for immunological studies. Deficient dietary Arg intensified acute changes in differential blood counts and weight gain during LPS-induced inflammation.

Implications of genetic selection on yolk proportion on the dry matter content of eggs in a White Leghorn population

1. The responses to genetic selection on yolk proportion as a technique for increasing egg dry matter content, an important criterion for the egg-product industry, was investigated in a pedigree flock of White Leghorn hens. 2. Parents were preselected on high and low yolk proportion from a base population. The absolute estimated breeding value for yolk proportion of both groups differed by 3%. The realised selection difference in dry matter content of eggs between groups was more than 1% in the analysed offspring population. 3. Heritability estimates were moderate and dry matter had a lower heritability (h(2) = 0.39) than yolk proportion (h(2) = 0.44). 4. The genetic correlation between yolk proportion and dry matter content was highly positive (rg = 0.91). Genetic correlations with egg weight were negative and would have to be compensated for in a breeding programme (rg = -0.76 with yolk proportion and rg = -0.64 with dry matter content). The genetic correlation between the laying performance and yolk proportion was rg = 0.28 and close to zero (rg = -0.05) for dry matter content. 5. Easy recording and lower undesirable correlations make yolk proportion more suitable for commercial selection compared with egg dry matter content in layer breeding.

Genome-wide association study for egg production and quality in layer chickens

Discovery of genes with large effects on economically important traits has for many years been of interest to breeders. The development of SNP panels which cover the whole genome with high density and, more importantly, that can be genotyped on large numbers of individuals at relatively low cost, has opened new opportunities for genome-wide association studies (GWAS). The objective of this study was to find genomic regions associated with egg production and quality traits in layers using analysis methods developed for the purpose of whole genome prediction. Genotypes on over 4500 birds and phenotypes on over 13,000 hens from eight generations of a brown egg layer line were used. Birds were genotyped with a custom 42K Illumina SNP chip. Recorded traits included two egg production and 11 egg quality traits (puncture score, albumen height, yolk weight and shell colour) at early and late stages of production, as well as body weight and age at first egg. Egg weight was previously analysed by Wolc et al. (2012). The Bayesian whole genome prediction model--BayesB (Meuwissen et al. 2001) was used to locate 1 Mb regions that were most strongly associated with each trait. The posterior probability of a 1 Mb window contributing to genetic variation was used as the criterion for suggesting the presence of a quantitative trait locus (QTL) in that window. Depending upon the trait, from 1 to 7 significant (posterior probability >0.9) 1 Mb regions were found. The largest QTL, a region explaining 32% of genetic variance, was found on chr4 at 78 Mb for body weight but had pleiotropic effects on other traits. For the other traits, the largest effects were much smaller, explaining <7% of genetic variance, with regions on chromosomes 2, 12 and 17 explaining above 5% of genetic variance for albumen height, shell colour and egg production, respectively. In total, 45 of 1043 1 Mb windows were estimated to have a non-zero effect with posterior probability > 0.9 for one or more traits.

Higher precision level at individual laying performance tests in noncage housing systems

With the Weihenstephan funnel nest box, 12 laying hen flocks were tested for their individual laying performance, egg quality, and nesting behavior in a noncage environment. During the whole observation period of 8 yr, a transponder-based data recording system was continuously improved and resulted in a recording accuracy of 97%. At peak production, heritabilities for the number of eggs laid are in some flocks higher than expected. With improved data accuracy, heritability estimates on individual egg weights are more stable. Heritabilities for nesting behavior traits range between a low to moderate level, providing very useful information for laying hen selection to help improve traits that cannot be recorded in cages. Over the years, the benefits of the Weihenstephan funnel nest box for laying hen breeders have grown. This is due to higher data recording accuracies and extended testing capacities, which result in more reliable genetic parameters.

Analysis of egg production in layer chickens using a random regression model with genomic relationships

Random regression models allow for analysis of longitudinal data, which together with the use of genomic information are expected to increase accuracy of selection, when compared with analyzing average or total production with pedigree information. The objective of this study was to estimate variance components for egg production over time in a commercial brown egg layer population using genomic relationship information. A random regression reduced animal model with a marker-based relationship matrix was used to estimate genomic breeding values of 3,908 genotyped animals from 6 generations. The first 5 generations were used for training, and predictions were validated in generation 6. Daily egg production up to 46 wk in lay was accumulated into 85,462 biweekly (every 2 wk) records for training, of which 17,570 were recorded on genotyped hens and the remaining on their nongenotyped progeny. The effect of adding additional egg production data of 2,167 nongenotyped sibs of selection candidates [16,037 biweekly (every 2 wk) records] to the training data was also investigated. The model included a 5th order Legendre polynomial nested within hatch-week as fixed effects and random terms for coefficients of quadratic polynomials for genetic and permanent environmental components. Residual variance was assumed heterogeneous among 2-wk periods. Models using pedigree and genomic relationships were compared. Estimates of residual variance were very similar under both models, but the model with genomic relationships resulted in a larger estimate of genetic variance. Heritability estimates increased with age up to mid production and decreased afterward, resulting in an average heritability of 0.20 and 0.33 for pedigree and genomic models. Prediction of total egg number was more accurate with the genomic than with the pedigree-based random regression model (correlation in validation 0.26 vs. 0.16). The genomic model outperformed the pedigree model in most of the 2-wk periods. Thus, results of this study show that random regression reduced animal models can be used in breeding programs using genomic information and can result in substantial improvements in the accuracy of selection for trajectory traits.

Enhancing the egg's natural defence against bacterial penetration by increasing cuticle deposition

The cuticle is a proteinaceous layer covering the avian egg and is believed to form a defence to microorganism ingress. In birds that lay eggs in challenging environments, the cuticle is thicker, suggesting evolutionary pressure; however, in poultry, selection pressure for this trait has been removed because of artificial incubation. This study aimed to quantify cuticle deposition and to estimate its genetic parameters and its role on trans-shell penetration of bacteria. Additionally, cuticle proteins were characterised to establish whether alleles for these genes explained variation in deposition. A novel and reliable quantification was achieved using the difference in reflectance of the egg at 650 nm before and after staining with a specific dye. The heritability of this novel measurement was moderate (0.27), and bacteria penetration was dependent on the natural variation in cuticle deposition. Eggs with the best cuticle were never penetrated by bacteria (P < 0.001). The cuticle proteome consisted of six major proteins. A significant association was found between alleles of one of these protein genes, ovocleidin-116 (MEPE), and cuticle deposition (P = 0.015) and also between alleles of estrogen receptor 1 (ESR1) gene and cuticle deposition (P = 0.008). With the heritability observed, genetic selection should be possible to increase cuticle deposition in commercial poultry, so reducing trans-generational transmission of microorganisms and reversing the lack of selection pressure for this trait during recent domestication.

Genetic variation in eggshell crystal size and orientation is large and these traits are correlated with shell thickness and are associated with eggshell matrix protein markers

The size and orientation of calcium carbonate crystals influence the structure and strength of the eggshells of chickens. In this study, estimates of heritability were found to be high (0.6) for crystal size and moderate (0.3) for crystal orientation. There was a strong positive correlation (0.65) for crystal size and orientation with the thickness of the shell and, in particular, with the thickness of the mammillary layer. Correlations with shell breaking strength were positive but with a high standard error. This was contrary to expectations, as in man-made materials smaller crystals would be stronger. We believe the results of this study support the hypothesis that the structural organization of shell, and in particular the mammillary layer, is influenced by crystal size and orientation, especially during the initial phase of calcification. Genetic associations for crystal measurements were observed between haplotype blocks or individual markers for a number of eggshell matrix proteins. Ovalbumin and ovotransferrin (LTF) markers for example were associated with crystal size, while ovocleidin-116 and ovocalyxin-32 (RARRES1) markers were associated with crystal orientation. The location of these proteins in the eggshell is consistent with different phases of the shell-formation process. In conclusion, the variability of crystal size, and to a lesser extent orientation, appears to have a large genetic component, and the formation of calcite crystals are intimately related to the ultrastructure of the eggshell. Moreover, this study also provides evidence that proteins in the shell influence the variability of crystal traits and, in turn, the shell's thickness profile. The crystal measurements and/or the associated genetic markers may therefore prove to be useful in selection programs to improve eggshell quality.

Quantitative trait loci affecting eggshell traits in an F(2) population

Good eggshell quality is important for both table egg quality and chicken reproductive performance. Weak eggshells cause economic losses in all production steps. Poor eggshell quality also poses increased risk for Salmonella infections. Eggshell quality has been a difficult trait to improve by traditional breeding, as it can be measured only for females and it is difficult and expensive to measure. Breeding for improved shell quality may therefore benefit from the use of marker-assisted selection. In an effort to find markers linked to eggshell quality, we have used an F(2) population of 668 females to map quantitative trait loci (QTL) affecting eggshell traits (eggshell deformation, breaking force, weight). By using 160 microsatellite markers on 27 chromosomes, we found 11 genome-wide and 15 suggestive QTL for shell traits measured at different times during production. Loci affecting the deformation were found on chromosomes 1, 2, 6, 10, 14 and Z. Loci affecting the breaking force were detected on chromosomes 2, 3, 10, 12 and Z. Loci affecting the shell weight were detected on chromosomes 6, 12, 24 and Z. Each QTL explains between 1.5% and 4.6% of the phenotypic variance, adding up to 10-15% of total phenotypic variance explained for the different traits. No epistatic effects were observed between loci affecting eggshell traits. Because the effects for quality are mainly additive, these results provide a basis for further characterization of the loci to identify closely linked markers to be used in marker-assisted selection.

Breeding to reduce susceptibility to Escherichia coli in layers

Colibacillosis is a bacterial disease of great concern in the layer industry causing substantial animal and economic losses worldwide. Breeding for resistance to colibacillosis is an important control strategy that would complement traditional management strategies such as vaccinations and therapeutic treatments. Because antibiotic use in animal production is expected to substantially decrease in the future to meet not only consumer demands but also regulations, it is expected that bacterial diseases such as colibacillosis will become even more important. A challenge test was carried out on 353 pedigreed White Leghorn female chickens of 1 pure line. The birds were inoculated with Escherichia coli at an age of 93 to 95 wk (3 hatches) and symptoms of disease and mortality were constantly monitored for up to 6 d after inoculation. The cumulative mortality was 64%, the majority of which took place in the first 2 d. In the present study, genetic parameters of resistance to colibacillosis were estimated to judge the value of genetic selection. The heritability for survival rate was 0.17+/-0.07. Both for quantitative as well as for qualitative traits of economic interest, there was no remarkable difference between survivors and hens that died. Data showed that it is in principle possible to breed for colibacillosis resistance without penalizing the improvement in other key traits. The B21 marker for MHC in this study was associated with a lower colibacillosis susceptibility. In this study, it was demonstrated that it is possible to breed for Escherichia coli resistance. However, due to the inconveniences of a challenge test, it would be very interesting to make use of MAS.

Genetische Analyse des Legemusters in der Bodenhaltung im Hinblick auf neue Leistungsprüfungskriterien für die Legehennenzucht

Abstract. Title of the paper: Genetic analysis of the laying pattern in floor management in terms of new performance parameters for breeding In order to facilitate a specific selection of laying hens which are suitable for alternative housing systems, it will be of advantage if the individual hens were tested in their later husbandry environment. Therefore, a new technology has been developed, the »Weihenstephan Funnel Nest Box«, which enables the automatic recording of these essential performance and nesting behaviour parameters of the individual hens in a group housing system. The exact oviposition times of 263 laying hens of Lohmann Silver line were recorded and used to analyse the laying pattern. Some results which were already pointed out in literature were thus confirmed, other brought new cognitions in terms of the oviposition pattern and about the pause following a laying sequence. A positive genetic correlation between the length of a laying sequence and the subsequent pause durations (rg=+0.49) confirmed the tendency to longer breaks following an increasing laying sequence. The duration of a break was, however, not such an essential criteria for the productivity of a hen. More important in this context was the number of pauses which rises constantly with the number of laying sequences over the whole observation period. When the hens laid in shorter sequences, it was observed that the proportion of sequences grew, which was reflected as smaller number of registered eggs per hen (rg =−0.73). The logical conclusion was the highly positive correlation between the length of a laying sequence and the number of registered eggs (rg =+0.82). Closely associated with the length of a laying sequence, as well as the laying performance, was the parameter time interval between two laid eggs. The time interval between two laid eggs was significant shortened from the first to the third egg within one laying sequence and eventually reached for more than 24 h for most of the hens. The phenotypic and genetic correlation between the time interval and the laying performance was negative (rp =−0.46 and rg =−0.46). The heritability for the time interval was estimated at h²=0.17 which was similar to the heritability for number of eggs (h²=0.20). Slightly higher heritabilities were estimated for the indirect parameter of the time interval, the oviposition time of the third to the fifth egg in a laying sequence (h²=0.25, h²=0.34 and h²=0.29). Valuations in this range would be in regard of new performance testing parameter competitive to the parameter number of eggs and therefore, be tested in further investigations.

Variation in neighbouring genes of the dopaminergic and serotonergic systems affects feather pecking behaviour of laying hens

Feather pecking is a behavioural disorder of laying hens and has serious animal welfare and economic implications. One of the several aetiological hypotheses proposes that the disorder results from redirected exploratory behaviour. Variation in the gene encoding the dopamine D4 receptor (DRD4) has been shown to be associated with exploratory behaviour in several species, including in a passerine bird species. We therefore considered DRD4 as a candidate gene for feather pecking. We have annotated DRD4 in the chicken genome and have re-sequenced it in 140 animals belonging to: experimental layer lines divergently selected for high and low propensity to feather pecking; the unselected founder population; and two commercial lines with low and high propensity to feather pecking. We have identified two sub-haplotypes of DRD4 that are highly significantly associated with feather pecking behaviour in the experimental (P = 7.30 x 10(-7)) as well as in the commercial lines (P = 2.78 x 10(-6)). Linkage disequilibrium (LD) extends into a neighbouring gene encoding deformed epidermal autoregulatory factor 1 (DEAF1). The product of DEAF1 regulates the transcription of the gene encoding the serotonin (5-hydroxytryptamine) 1A receptor. Thus, DEAF1 represents another candidate gene for feather pecking. Re-sequencing of five animals homozygous for the 'low-pecking' sub-haplotype and of six animals homozygous for the 'high-pecking' sub-haplotype delineated an LD block of 14 833 bases spanning the two genes. None of the variants in the LD block is obviously functional. However, the haplotype information will be useful to select against the propensity to feather pecking in chicken and to elucidate the functional implications of the variants.

Polymorphisms in eggshell organic matrix genes are associated with eggshell quality measurements in pedigree Rhode Island Red hens

Novel and traditional eggshell quality measurements were made from up to 2000 commercial pedigree hens for a candidate gene association analysis with organic eggshell matrix genes: ovocleidin-116, osteopontin (SPP1), ovocalyxin-32 (RARRES1), ovotransferrin (LTF), ovalbumin and ovocalyxin-36, as well as key genes in the maintenance and function of the shell gland [estrogen receptor (ESR1) and carbonic anhydrase II (CAII)]. Associations were found for (i) ovalbumin with breaking strength and shell thickness; (ii) ovocleidin-116 with elastic modulus, shell thickness and egg shape; (iii) RARRES1 with mammillary layer thickness; (iv) ESR1 with dynamic stiffness; (v) SPP1 with fracture toughness and (vi) CAII with egg shape. The marker effects are as large as 17% of trait standard deviations and could be used to improve eggshell quality.

Variance component and breeding value estimation for reproductive traits in laying hens using a Bayesian threshold model

Variance components and breeding values were estimated for 3 reproductive traits in a pure line of White Leghorn laying hens. The traits were proportion of fertile eggs of eggs set, proportion of first quality chicks of eggs set, and proportion of first-quality chicks of fertile eggs. A total of 3,020 hens were tested up to 3 times over a period of 7 d. For the definition of the traits, each egg was scored for each trait either as 0 or 1. To account for the binomial distribution of the data, a Bayesian animal threshold model implemented in a Gibbs sampler was applied that considered the record of each egg set as a repeated observation of the hen. The estimated heritability was 0.067, 0.126, and 0.136 for the traits proportion of fertile eggs of eggs set, proportion of first quality chicks of eggs set, and proportion of first-quality chicks of fertile eggs, respectively, and the SE were small. It was shown that the heritability estimates were substantially higher from their expected values based on linear models. This results in a higher genetic progress and consequently favors the applied Bayesian threshold model for a genetic evaluation of binomial distributed reproductive traits.

A QTL for osteoporosis detected in an F2 population derived from White Leghorn chicken lines divergently selected for bone index

Osteoporosis, resulting from progressive loss of structural bone during the period of egg-laying in hens, is associated with an increased susceptibility to bone breakage. To study the genetic basis of bone strength, an F(2) cross was produced from lines of hens that had been divergently selected for bone index from a commercial pedigreed White Leghorn population. Quantitative trait loci (QTL) affecting the bone index and component traits of the index (tibiotarsal and humeral strength and keel radiographic density) were mapped using phenotypic data from 372 F(2) individuals in 32 F(1) families. Genotypes for 136 microsatellite markers in 27 linkage groups covering approximately 80% of the genome were analysed for association with phenotypes using within-family regression analyses. There was one significant QTL on chromosome 1 for bone index and the component traits of tibiotarsal and humeral breaking strength. Additive effects for tibiotarsal breaking strength represented 34% of the trait standard deviation and 7.6% of the phenotypic variance of the trait. These QTL for bone quality in poultry are directly relevant to commercial populations.

Heritability and genetic correlation of measurements derived from acoustic resonance frequency analysis; a novel method of determining eggshell quality in domestic hens

Cracked eggshells result in economic loss and provide a route for pathogenic organisms to enter the egg. Genetic factors that contribute to shell strength are likely to decrease the risk that an egg will crack when subject to insult. A novel measurement, the dynamic stiffness of the eggshell (Kdyn) was examined to determine if it might be used in the genetic selection of hens with improved eggshell characteristics. The measurement is determined from acoustic resonance frequency analysis. The estimates of heritability for the novel measurement of Kdyn were moderately high and ranged from 0.33 to 0.53 depending on the model used for the estimation. The estimates of genetic correlation of Kdyn with eggshell breaking strength (0.49) and static stiffness (0.57) were positive and relatively large as expected. There was a small negative genetic correlation between Kdyn and egg production from 26 to 50 weeks of age (-0.19) and a moderate one from 58 to 74 weeks of age (-0.36). The moderate heritability and relative independence of Kdyn indicates that this measurement could be used successfully in a breeding programme to improve shell quality and to reduce the incidence of cracks.

Fishy taint in chicken eggs is associated with a substitution within a conserved motif of the gene

Fishy odor of urine and other secretions is a characteristic of trimethylaminuria in humans, resulting from loss-of-function mutations in the flavin-containing mono-oxygenase isoform FMO3. A similar phenotype exists in cattle, in which a nonsense mutation in the bovine orthologue causes fishy off-flavor in cow's milk. The fishy odor is caused by an elevated level of excreted odorous trimethylamine (TMA), due to deficient oxidation of TMA. We report the mapping of a similar disorder (fishy taint of eggs) and the chicken FMO3 gene to chicken chromosome 8. The only nonsynonymous mutation identified in the chicken FMO3 gene (T329S) changes an evolutionarily highly conserved amino acid and is associated with elevated levels of TMA and fishy taint in the egg yolk in several chicken lines. No differences in the expression of FMO3 were found among individuals with different associated genotypes, indicating that the trait is not caused by a linked polymorphism causing altered expression of the gene. The results support the importance and function of the evolutionarily conserved motif FATGY, which has been speculated to be a substrate recognition pocket of N-hydroxylating siderophore enzymes and flavin-containing mono-oxygenases.

Estimation of genetic parameters based on individual and group mean records in laying hens

(1) The study was conducted to estimate the heritability, genetic correlations and breeding values of laying hens based on individual records and group mean records. (2) Records of two pure lines from a commercial breeding programme of White Leghorns from three generations housed in single cages and in group cages were used. A total of 8483 and 8817 individual records of lines A and D, respectively, and a total of 1358 (line A) and 1161 (line D) group mean records were analysed. (3) An animal model using Restricted Maximum Likelihood (REML) was used to estimate variance components of individual records. Group mean records were analysed using the sire model, taking heterogeneity of error variance and correlated residual effects into account. Breeding values of sires were estimated based on the BLUP method using a multivariate sire model. Spearman Rank correlations were used to compare sire breeding values estimated from individual records and from group mean records. The traits studied were monthly egg production, cumulative production and egg weight. (4) Heritability estimates based on individual records were higher than from group mean records. Heritabilities for cumulative production records were higher than for monthly production, based on individual as well as group mean records. The estimates of genetic correlations between monthly egg production and cumulative production were moderate to high. Egg production and egg weight recorded individually were highly genetically correlated with those recorded on group means. Sire breeding values estimated from individual records showed high correlations with those from group mean records. (5) Differences in the ranking of sire breeding values estimated from individual vs group mean records were negligible, indicating that no genotype x environment interaction exists. Selection based on individual performance records of laying hens housed in single cages could give a good response on performance of laying hens housed in group cages. Cumulative egg production over periods 1 to 6 is the best trait for the selection programme.

Genetische Parameter für Merkmale der Eiproduktion geschätzt mit additiven und Dominanzmodellen bei Legehennen

Abstract. Title of the paper: Genetic evaluation of egg production traits based on additive and dominance models in laying hens The study was conducted to estimate additive and dominance variances for egg production traits of two commercial purebred lines (A &amp; D) of laying hens using an animal model analysis. Breeding values estimated from a dominance model were compared to those from an additive model. In total, 8625 records of line A and 8968 records of line D from three generations were used in the analysis. Every record contained information on the number of eggs laid between 20 and 28 (EN1-2), 28 and 48 (EN3-7) and between 20 and 48 (EN1-7) weeks of age. Further average egg weight (EW), egg weight at 28 (EW1), 33 (EW2) and 40 (EW3) weeks of age were available. An additive animal model and one- and three-trait dominance models including the inbreeding coefficients as covariates were fitted to the data. Simultaneous estimates of the additive and dominance variance components were obtained using the REML method. The estimates of h2 from the dominance models for EN1-2, EN3-7, EN1-7 and EW were 0.40, 0.15, 0.28 and 0.62 for line A and 0.38, 0.16, 0.26 and 0.53 for line D. The ratios d2 of the dominance variance to total variance were moderate for EN (0.12–0.13) and low for EW (0.04–0.07) within line A but relatively low for EN (0.03–0.12) and high for EW (0.12–0.21) within line D. Between the breeding values of the best 100 hens of each generation estimated with the additive and the dominance models for EN1-2, EN3-7, EN1-7 and EW high rank correlations (0.946, 0.896, 0.945 and 0.991 in line A and 0.996, 0.899, 0.971 and 0.951 in line D were found

Genetic parameters for egg production and egg weight of laying hens housed in single and group cages

Abstract. The present study was conducted to estimate the heritability and genetic correlation of monthly egg production and egg weight of 2 lines White Leghorn hens in single and group cages. A total of 2289 records (line A) and 2596 records (line D) from single cages, 518 and 541 records (for line A and D, respectively) from group cages, were analysed. (Co) variance components of single cage data were analysed using the programme VCE4 applying the REML method and a multiple trait animal model. An EM-algorithm was used to obtain (co) variance components for group cage data. Genetic correlations between single and group cages were analysed using the programme VCE4 based on sire model. Heritability estimates for monthly egg production in single cages ranged from 0.08 to 0.44 (line A); 0.04 to 0.43 (line D) and those for group cages were 0.02 to 0.42 (line A); 0.02 to 0.19 (line D). Egg weight was highly heritable for single and group cages (heritability = 0.25 to 0.54). The genetic correlations between monthly and cumulative egg production were 0.25 to 0.95 (line A); 0.26 to 0.86 (line D) for single cage and 0.24 to 0.84 (line A); 0.26 to 0.96 (line D) for group cage. Cumulative egg production in single cage were highly correlated with those of group cages (0.89 and 0.63, respectively for line A and line D). Single cage records gave higher estimates of genetic parameter than group records. However, the trend of estimates is almost the same. High genetic correlations were found between single- and group cages in most of the production periods.

Genetic differences of Ascaridia galli egg output in laying hens following a single dose infection

Groups of 20-week-old white (Lohmann LSL) and brown (Lohmann Brown) hens were reared under helminth-free conditions and both divided into two subgroups. One subgroup was artificially infected with 250 embryonated Ascaridia galli eggs, the other subgroup were kept as uninfected controls. During the following 12-month laying period individual faecal Ascaridia egg counts (FEC) were performed and bodyweight measured at monthly intervals. Laying performance and egg weights were determined daily. The mean FEC were significantly (P < 0.01) higher in infected white hens than in infected brown hens. The growth rate of the white hens was significantly (P < 0.05) higher in the control group, whereas in brown hens no significant group difference was observed. The laying performances and egg weights did not differ significantly (P > 0.05) between control and infected animals for either line. The estimated repeatabilities for mean log(10) FEC of different samples were reasonably high (0.16-0.54). Heritabilities for mean log(10) FEC were between 0.13 and 0.19 for white hens and between 0.0 and 0.10 for brown hens. Thus, it should be possible to select for A. galli resistance in chickens, which will be of importance for birds kept in alternative and organic farming systems.

Bedeutung der Varianzkomponentenschätzung für die Zucht von landwirtschaftlichen Nutztieren – eine Übersicht

Abstract. Title of the paper: The importance of variance components estimation in breeding of farm animals – a review The present paper showed the importance of variance components estimation in animal breeding. Beside the use of variance components for estimation of breeding values, the components have a high importance on further breeding aspects, such as indication of selection limits, optimisation of test period, change of Performance during growth, and determination of the best selection traits. Maternal and non-additive genetic variance components can be estimated and their high influence on choice of the optimal selection strategy are explained. Standard errors of crossbreeding parameters are influenced by genetic relationships and are only unbiased when using all genetic variances and covariances among animals. Genotype-environmental-interaction and heterogeneous variances, which result in high reduction in selection response, can be obtained in a variance components estimation. The high value of Bayesian methods in order to describe the sampling variance of variance components and to account for the Standard error of estimation of variance components in the estimation of breeding values is explained.

[The analysis of selected performance parameters following embryo transfer in the example of cattle]

Gestation lengths and birth weight of calves from German Red Pied cows were used to analyse differences between embryo transplant offsprings (n = 76) and offsprings from natural pregnancy (n = 118). Furthermore differences were examined in milk traits between embryo transplant (n = 76) and not embryo transplant offsprings (n = 66) from the same dam (German Black Pied, n = 38). After embryo transfer gestation lengths was shorter, but only with a clear difference in first calving cows. Calves from embryo transfer had lower birth weights, because most of the time recipients are maiden. Even the age effect was taken into account, birth weights were about 1.5 kg lower for embryo transplant offsprings. For milk traits no significant differences could be ascertain between embryo transplant and not embryo transplant offsprings. With the exception of fat yield the estimated breeding values of the offsprings correspond to the expectations.