Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Exploiting whole genome sequence variants in cattle breeding : Unraveling the distribution of genetic variants and role of rare variants in genomic evaluation
    Zhang, Qianqian - \ 2017
    Wageningen University. Promotor(en): H. Bovenhuis; M.S. Lund, co-promotor(en): G. Sahana; M. Calus; B. Guldbrandtsen. - Wageningen : Wageningen University - ISBN 9788793643147 - 249
    cattle - genomes - genetic variation - inbreeding - homozygosity - longevity - quantitative traits - animal breeding - animal genetics - rundvee - genomen - genetische variatie - inteelt - homozygotie - gebruiksduur - kwantitatieve kenmerken - dierveredeling - diergenetica

    The availability of whole genome sequence data enables to better explore the genetic mechanisms underlying different quantitative traits that are targeted in animal breeding. This thesis presents different strategies and perspectives on utilization of whole genome sequence variants in cattle breeding. Using whole genome sequence variants, I show the genetic variation, recent and ancient inbreeding, and genome-wide pattern of introgression across the demographic and breeding history in different cattle populations. Using the latest genomic tools, I demonstrate that recent inbreeding can accurately be estimated by runs of homozygosity (ROH). This can further be utilized in breeding programs to control inbreeding in breeding programs. In chapter 2 and 4, by in-depth genomic analysis on whole genome sequence data, I demonstrate that the distribution of functional genetic variants in ROH regions and introgressed haplotypes was shaped by recent selective breeding in cattle populations. The contribution of whole genome sequence variants to the phenotypic variation partly depends on their allele frequencies. Common variants associated with different traits have been identified and explain a considerable proportion of the genetic variance. For example, common variants from whole genome sequence associated with longevity have been identified in chapter 5. However, the identified common variants cannot explain the full genetic variance, and rare variants might play an important role here. Rare variants may account for a large proportion of the whole genome sequence variants, but are often ignored in genomic evaluation, partly because of difficulty to identify associations between rare variants and phenotypes. I compared the powers of different gene-based association mapping methods that combine the rare variants within a gene using a simulation study. Those gene- based methods had a higher power for mapping rare variants compared with mixed linear models applying single marker tests that are commonly used for common variants. Moreover, I explored the role of rare and low-frequency variants in the variation of different complex traits and their impact on genomic prediction reliability. Rare and low-frequency variants contributed relatively more to variation for health-related traits than production traits, reflecting the potential of improving prediction reliability using rare and low-frequency variants for health-related traits. However, in practice, only marginal improvement was observed using selected rare and low-frequency variants when combined with 50k SNP genotype data on the reliability of genomic prediction for fertility, longevity and health traits. A simulation study did show that reliability of genomic prediction could be improved provided that causal rare and low-frequency variants affecting a trait are known.

    The genetic background of bovine αs1- and αs2-casein phosphorylation
    Fang, Zih-Hua - \ 2017
    Wageningen University. Promotor(en): E. Verrier; H. Bovenhuis, co-promotor(en): P. Martin; M.H.P.W. Visker. - Wageningen : Wageningen University - ISBN 9789463438148 - 141
    dairy cattle - alpha-s1-casein - alpha-s2-casein - phosphorylation - milk composition - milk proteins - genetic variation - genetic factors - animal genetics - melkvee - alfa-s-1-caseïne - alfa-s-2-caseïne - fosforylering - melksamenstelling - melkeiwitten - genetische variatie - genetische factoren - diergenetica

    Phosphorylation of caseins (CN) is a crucial post-translational modification allowing caseins to aggregate as micelles. The formation and stability of casein micelles are important for transporting abundant minerals to the neonate and manufacturing of dairy products. Therefore, it is of great interest to explore variation in degrees of phosphorylation of caseins and study to what extent genetic and other factors contribute to this variation. This thesis aimed to investigate the genetic background of bovine milk protein composition with a focus on phosphorylation of αs1- and αs2-CN. Two studies were conducted to quantify phosphorylation levels of αs1- and αs2-CN: one in French Montbéliarde using liquid chromatography coupled with electrospray ionization mass spectrometry and the other in Dutch Holstein Friesian using capillary zone electrophoresis. In French Montbéliarde, in addition to the known isoforms αs1-CN-8P and-9P and αs2-CN-10P to -13P, three new phosphorylation isoforms were detected, namely αs2-CN-9P, αs2-CN-14P, and αs2-CN-15P. Relative concentrations of the phosphorylation isoforms varied considerably among cows. Phenotypic correlations showed that isoforms phosphorylated at higher degrees (αs1-CN-9P and αs2-CN-12P to -14P) correlated negatively with isoforms phosphorylated at lower degrees (αs1-CN-8P, αs2-CN-10P, and -11P). Furthermore, it was shown that αs1- and αs2-CN phosphorylation profiles changed across parity and lactation, and exploitable genetic variation for the phosphorylation degrees of αs1- and αs2-CN (defined as the proportion of higher-degree isoforms in αs1- and αs2-CN, respectively) exist. In Dutch Holstein Friesian, three αs2-CN isoforms, namely αs2-CN-10P to -12P, and the phosphorylation degrees of αs1- and αs2-CN were quantified. High intra-herd heritabilities were estimated for individual αs2-CN phosphorylation isoforms and the phosphorylation degrees of αs1- and αs2-CN (ranging from 0.54 to 0.89). This suggests that genetic factors contribute substantially to observed differences in αs1- and αs2-CN phosphorylation profiles. The highly positive correlation between the phosphorylation degrees of αs1- and αs2-CN (0.94) suggest that phosphorylation of αs1- and αs2-CN is related. Additionally, a total of 10 regions, distributed across Bos taurus autosomes (BTA) 1, 2, 6, 9, 11, 14, 15, 18, 24 and 28, were detected to be associated with individual αs1- and αs2-CN phosphorylation isoforms and their phosphorylation degrees. Regions on BTA1, 6, 11 and 14 were associated with multiple traits studied. Two quantitative trait loci (QTL) regions were detected on BTA1: one affecting αs2-CN production, and the other affecting αs1-CN PD and αs2-CN PD. The QTL region on BTA6 affected only individual αs2-CN isoforms. The QTL region on BTA11 and 14 affected relative concentrations of αs2-CN-10P and αs2-CN-11P, αs1-CN PD and αs2-CN PD. Results suggested that effects of identified genomic regions on αs1-CN PD and αs2-CN PD are probably due to changes in milk synthesis and phosphorus secretion in milk.

    Milk progesterone measures to improve genomic selection for fertility in dairy cows
    Tenghe, Amabel Manyu Mefru - \ 2017
    Wageningen University. Promotor(en): R.F. Veerkamp; B. Berglund, co-promotor(en): D. J. de Koning; A.C. Bouwman. - Wageningen : Wageningen University - ISBN 9789463431330 - 179
    dairy cows - fertility - progesterone - milk - genomics - genetic improvement - heritability - genetic parameters - dairy performance - reproductive traits - animal genetics - animal breeding - dairy farming - melkkoeien - vruchtbaarheid - progesteron - melk - genomica - genetische verbetering - heritability - genetische parameters - melkresultaten - voortplantingskenmerken - diergenetica - dierveredeling - melkveehouderij

    Improved reproductive performance has a substantial benefit for the overall profitability of dairy cattle farming by decreasing insemination and veterinary treatment costs, shortening calving intervals, and lowering the rate of involuntary culling. Unfortunately, the low heritability of classical fertility traits derived from calving and insemination data makes genetic improvement by traditional animal breeding slow. Therefore, there is an interest in finding novel measures of fertility that have a higher heritability or using genomic information to aid genetic selection for fertility. The overall objective of this thesis was to explore the use of milk progesterone (P4) records and genomic information to improve selection for fertility in dairy cows. In a first step, the use of in-line milk progesterone records to define endocrine fertility traits was investigated, and genetic parameters estimated. Several defined endocrine fertility traits were heritable, and showed a reasonable repeatability. Also, the genetic correlation of milk production traits with endocrine fertility traits were considerably lower than the correlations of milk production with classical fertility traits. In the next step 17 quantitative trait loci (QTL) associated with endocrine fertility traits, were identified on Bos taurus autosomes (BTA) 2, 3, 8, 12, 15, 17, 23, and 25 in a genome-wide association study with single nucleotide polymorphisms. Further, fine-mapping of target regions on BTA 2 and 3, identified several associated variants and potential candidate genes underlying endocrine fertility traits. Subsequently, the optimal use of endocrine fertility traits in genomic evaluations was investigated; using empirical and theoretical predictions for single-trait models, I showed that endocrine fertility traits have more predictive ability than classical fertility traits. The accuracy of genomic prediction was also substantially improved when endocrine and classical fertility traits were combined in multi-trait genomic prediction. Finally, using deterministic predictions, the potential accuracy of multi-trait genomic selection when combining a cow training population measured for the endocrine trait commencement of luteal activity (C-LA), with a training population of bulls with daughter observations for a classical fertility trait was investigated. Results showed that for prediction of fertility, there is no benefit of investing in a cow training population when the breeding goal is based on classical fertility traits. However, when considering a more biological breeding goal for fertility like C-LA, accuracy is substantially improved when endocrine traits are available from a limited number of farms.

    Genetic improvement of feed intake and methane emissions of cattle
    Manzanilla Pech, Coralia I.V. - \ 2017
    Wageningen University. Promotor(en): Roel Veerkamp, co-promotor(en): Yvette de Haas. - Wageningen : Wageningen University - ISBN 9789463430692 - 199
    cattle - feed intake - methane production - genetic improvement - genetic parameters - conformation - breeding value - animal genetics - rundvee - voeropname - methaanproductie - genetische verbetering - genetische parameters - bouw (dier) - fokwaarde - diergenetica

    Feed costs represent half of the total costs of dairy production. One way to increase profitability of dairy production is to reduce feed costs by improving feed efficiency. As DMI is a trait that varies significantly during and across lactations, it is imperative to understand the underlying genetic architecture of DMI across lactation. Moreover, phenotypes of DMI are scarce, due to the difficulty of recording them (expensive and labor-intensive). Some predictor traits have been suggested to predict DMI. Examples of these predictor traits are those related to production (milk yield (MY) or milk content) or to the maintenance of the cow (body weight (BW) or conformation traits). The ability to determine when predictor traits ideally should be measured in order to achieve an accurate prediction of DMI throughout the whole lactation period is thus important. Recently, with the use of information of single nucleotide polymorphism (SNP) markers, together with phenotypic data and pedigree, genomically estimated breeding values (GEBV) of scarcely recorded traits, such as DMI, have become easier to accurately predict. This approach, combined with predictor traits, could contribute to an increased accuracy of predictions of GEBV of DMI. Methane (CH4) is the second important greenhouse gas, and enteric CH4 is the largest source of anthropogenic CH4, representing 17% of global CH4 emissions. Furthermore, methane emissions represent 2-12% of feed energy losses. Selecting for lower CH4 emitting animals and more feed-efficient animals would aid in mitigating global CH4 emissions. To identify the impact on CH4 emissions of selecting for lower DMI animals, it is important to determine the correlations between DMI and CH4 and to identify whether the same genes that control DMI affect CH4. Therefore, the general objectives of this thesis were to (1) explore the genetic architecture of DMI during lactation, (2) study the relationship of DMI to conformation, production and other related traits, (3) investigate the correlations between DMI and methane traits, and determine the SNP in common between DMI and CH4 through a genome-wide association study (GWAS), and (4) investigate the accuracy of predictions of DMI using predictor traits combined with genomic data.

    Genetic improvement of longevity in dairy cows
    Pelt, Mathijs van - \ 2017
    Wageningen University. Promotor(en): Roel Veerkamp, co-promotor(en): T.H.E. Meuwissen. - Wageningen : Wageningen University - ISBN 9789463430821 - 188
    dairy cows - longevity - genetic improvement - breeding value - genetic analysis - survival - animal models - animal genetics - melkkoeien - gebruiksduur - genetische verbetering - fokwaarde - genetische analyse - overleving - diermodellen - diergenetica

    Improving longevity helps to increase the profit of the farmer, and it is seen as an important measure of improved animal welfare and sustainability of the sector. Breeding values for longevity have been published since in 1999 in the Netherlands. For AI-companies and farmers it is necessary that breeding values are accurately estimated and will remain stable for the rest of life. However, current breeding values for longevity of bulls seem to fluctuate more than expected. The main aim of this thesis was to revisit the genetics of longevity and develop a genetic evaluation model for longevity, where breeding values reflect the true breeding value quicker during early life and therefore breeding values become more stable. Genetic parameters were estimated for survival up to 72 months after first calving with a random regression model (RRM). Survival rates were higher in early life than later in life (99 vs. 95%). Survival was genetically not the same trait across the entire lifespan, because genetic correlations differ from unity between different time intervals, especially when intervals were further apart. Survival in the first year after first calving was investigated more in depth. Survival of heifers has improved considerably in the past 25 years, initially due to the focus on a high milk production. More recently, the importance of a high milk production for survival has been reduced. Therefore functional survival was defined as survival adjusted for within-herd production level. For survival the optimum age at first calving was around 24 months, whereas for functional survival calving before 24 months resulted in a higher survival. Over years, genetic correlations between survival in different 5-yr intervals were below unity, whereas for functional survival genetic correlations did not indicate that survival changed over years. This suggested that a genetic evaluation using historical data should analyze functional survival rather than survival. A new genetic evaluation system for longevity was developed based on a RRM analyzing functional survival. Based on the correlation between the first breeding value of a bull and his later breeding values, the ranking of bulls was shown to be more stable for RRM than the current genetic evaluation. Bias in breeding value was observed, mainly for bulls with a large proportion of living daughters. Adjusting for within-herd production level reduced this bias in the breeding values greatly. Before implementing this new model for genetic evaluation, the cause of this bias needs to be further investigated.

    Genetics of equine insect bite hypersensitivity and genetic diversity in horses
    Shrestha, Merina - \ 2017
    Wageningen University. Promotor(en): Henk Bovenhuis; D.J. de Koning, co-promotor(en): Bart Ducro; A.M. Johansson. - Wageningen : Wageningen University - ISBN 9789463430166
    paarden - equus - insectenbeten - overgevoeligheid - diergenetica - genetische diversiteit - genetische variatie - allergische reacties - horses - equus - insect bites - hypersensitivity - animal genetics - genetic diversity - genetic variation - allergic reactions

    Genetic variation contributing to the phenotypic variation was utilized in this thesis to understand the genetic background of a complex trait IBH, and to understand genetic diversity and relationships between various horse populations.

    IBH is the most common skin allergic disorder in horses, caused by bites of midges, predominantly Culicoides species. It affects various horse breeds worldwide. With no effective treatment, IBH degrades horse health and causes economic loss. In this thesis, we used genome-wide SNPs to identify regions contributing to genetic variance of IBH susceptibility. We also investigated influence of increased number of horses and dense SNPs on identification of genomic regions associated to IBH susceptibility. Multiple genomic regions with small effects were observed in Studies I-III. Interesting genomic regions in the Icelandic horse population across the studies I and II, was observed on chromosomes 1, 7, 10, 15 and 17. The percentage of the genetic variance explained by top ten windows increased from 3.07% (Study I) to 6.56% (Study II). Novel genomic regions were identified when number of Icelandic horses was increased in Study II. Using dense SNPs on the Exmoor pony population we identified novel genomic regions, on chr 8, associated to IBH susceptibility, though with borderline significance.

    In Study IV, pre-conceived understanding about evolutionary history of horse populations matched obtained results from investigation of genetic relationships within Dutch warmblood populations (pairwise mean FST ≤ 0.070), and within pony-like populations (pairwise mean FST ≤ 0.078). Horse populations with similar genetic background might share similar genetic components for IBH susceptibility. The Friesian horse population had lowest diversity (mean inbreeding coefficients: fi: 30.4%, fiROH= 22.2%) in Study IV and was genetically distinct (FST ranged from 0.13 to 0.17). This might be a result of a history of several population bottlenecks and selection on a closed breeding scheme. Low diversity in immunity related genes, observed in the Friesian horse population, might have led to increased prevalence of IBH. Similarly, low susceptibility of IBH in a warmblood population, KWPN sport horse population might be due to high genetic diversity ( =-6.9%). High genetic diversity in KWPN sport horse population might be a result of an open breeding scheme and interbreeding with other warmblood populations.

    Antibodies and longevity of dairy cattle : genetic analysis
    Klerk, B. de - \ 2016
    Wageningen University. Promotor(en): Johan van Arendonk, co-promotor(en): Jan van der Poel; Bart Ducro. - Wageningen : Wageningen University - ISBN 9789462577589 - 134
    dairy cattle - dairy cows - antibodies - longevity - genetic analysis - breeding value - genomes - genetic improvement - animal genetics - melkvee - melkkoeien - antilichamen - gebruiksduur - genetische analyse - fokwaarde - genomen - genetische verbetering - diergenetica

    The dairy sector has a big impact on food production for the growing world population and contributes substantially to the world economy. In order to produce food in a sustainable way, dairy cows need to be able to produce milk without problems and as long as possible. Therefore, breeding programs focuses on improvement of important traits for dairy cows. In order to improve desirable traits and obtain genetic gain there is a constant need for optimization of breeding programs and search for useful parameters to include within breeding programs. Over the last several decades, breeding in dairy cattle mainly focused on production and fertility traits, with less emphasis on health traits. Health problems, however, can cause substantial economic losses to the dairy industry. The economic losses, together with the rising awareness of animal welfare, increased herd size, and less attention for individual animals, have led to an increased need to focus more on health traits. Longevity is strongly related to disease resistance, since a more healthy cow will live a longer productive life (longevity). The identification of biomarkers and the detection of genes controlling health and longevity, would not only greatly enhance the understanding of such traits but also offer the opportunity to improve breeding schemes. The objectives of this thesis therefore were 1) to find an easy measurable disease resistance related biomarker in dairy cows, 2) identify the relation between antibodies and longevity, 3) identify genomic regions that are involved with antibody production/expression. In this thesis antibodies are investigated as parameter for longevity. Antibodies might be a novel parameter that enables selection of cows with an improved ability to stay healthy and to remain productive over a longer period of time. In this thesis antibodies bindiging the naive antigen keyhole limpet hemocyanin (KLH) were assumed to be natural antibodies. Antibodies binding bacteria-derived antigens lipoteichoic acid (LTA), lipopolysaccharide (LPS) and peptidoglycan (PGN) were assumed to be specific antibodies. In chapter 2 it was shown that levels of antibodies are heritable (up to h2 = 0.23). Additionally, antibody levels measured in milk and blood are genetically highly correlated (± 0.80) for the two studied isotypes (IgG and IgM). On the other hand, phenotypically, natural antibodies (from both IgG and IgM isotype) measured in milk cannot be interpreted as the same trait (phenotypic correlation = ± 0.40). In chapter 3 and 4 it was shown that levels of antibodies (both natural-and specific antibodies) showed a negative relation with longevity: first lactation cows with low IgM or IgG levels were found to have a longer productive life. When using estimated breeding values for longevity, only a significant relation was found between natural antibody level (IgM binding KLH) and longevity. Lastly chapter 5 reports on a genome-wide-association study (GWAS), to detect genes contributing to genetic variation in natural antibody level. For natural antibody isotype IgG, genomic regions with a significant association were found on chromosome 21 (BTA). These regions included genes have impact on in isotype class switching (from IgM to IgG). The gained knowledge on relations between antibodies and longevity and the gained insight on genes responsible for natural antibodies level make antibodies potential interesting biomarkers for longevity.

    Mapping and fine-mapping of genetic factors affecting bovine milk composition
    Duchemin, S.I. - \ 2016
    Wageningen University. Promotor(en): Johan van Arendonk, co-promotor(en): Henk Bovenhuis; Marleen Visker; Willem F. Fikse. - Wageningen : Wageningen University - ISBN 9789462577305 - 190
    dairy cows - dairy cattle - milk composition - milk fat - genetic factors - quantitative trait loci - genomics - genetic mapping - animal genetics - melkkoeien - melkvee - melksamenstelling - melkvet - genetische factoren - loci voor kwantitatief kenmerk - genomica - genetische kartering - diergenetica

    Duchemin, S.I. (2016). Mapping and fine-mapping of genetic factors affecting bovine milk composition. Joint PhD thesis, between Swedish University of Agricultural Sciences, Sweden and Wageningen University, the Netherlands

    Bovine milk is an important source of nutrients in Western diets. Unraveling the genetic background of bovine milk composition by finding genes associated with milk-fat composition and non-coagulation of milk were the main goals of this thesis. In Chapter 1, a brief description of phenotypes and genotypes used throughout the thesis is given. In Chapter 2, I calculated the genetic parameters for winter and summer milk-fat composition from ~2,000 Holstein-Friesian cows, and concluded that most of the fatty acids (FA) can be treated as genetically the same trait. The main differences between milk-fat composition between winter and summer milk samples are most likely due to differences in diets. In Chapter 3, I performed genome-wide association studies (GWAS) with imputed 777,000 single nucleotide polymorphism (SNP) genotypes. I targeted a quantitative trait locus (QTL) region on Bos taurus autosome (BTA) 17 previously identified with 50,000 SNP genotypes, and identified a region covering 5 mega-base pairs on BTA17 that explained a large proportion of the genetic variation in de novo synthesized milk FA. In Chapter 4, the availability of whole-genome sequences of keys ancestors of our population of cows allowed to fine-mapped BTA17 with imputed sequences. The resolution of the 5 mega base-pairs region substantially improved, which allowed the identification of the LA ribonucleoprotein domain family, member 1B (LARP1B) gene as the most likely candidate gene associated with de novo synthesized milk FA on BTA17. The LARP1B gene has not been associated with milk-fat composition before. In Chapter 5, I explored the genetic background of non-coagulation of bovine milk. I performed a GWAS with 777,000 SNP genotypes in 382 Swedish Red cows, and identified a region covering 7 mega base-pairs on BTA18 strongly associated with non-coagulation of milk. This region was further characterized by means of fine-mapping with imputed sequences. In addition, haplotypes were built, genetically differentiated by means of a phylogenetic tree, and tested in phenotype-genotype association studies. As a result, I identified the vacuolar protein sorting 35 homolog, mRNA (VPS35) gene, as candidate. The VPS35 gene has not been associated to milk composition before. In Chapter 6, the general discussion is presented. I start discussing the challenges with respect to high-density genotypes for gene discovery, and I continue discussing future possibilities to expand gene discovery studies, with which I propose some alternatives to identify causal variants underlying complex traits in cattle.

    Genomic selection in egg-laying chickens
    Heidaritabar, M. - \ 2016
    Wageningen University. Promotor(en): Martien Groenen, co-promotor(en): John Bastiaansen. - Wageningen : Wageningen University - ISBN 9789462576704 - 220
    hens - genomics - genetic variation - selective breeding - quantitative traits - breeding value - animal genetics - animal breeding - hennen - genomica - genetische variatie - selectief fokken - kwantitatieve kenmerken - fokwaarde - diergenetica - dierveredeling


    Heidaritabar, M. (2016). Genomic selection in egg-laying chickens. PhD thesis, Wageningen University, the Netherlands

    In recent years, prediction of genetic values with DNA markers, or genomic selection (GS), has become a very intense field of research. Many initial studies on GS have focused on the accuracy of predicting the genetic values with different genomic prediction methods. In this thesis, I assessed several aspects of GS. I started with evaluating results of GS against results of traditional pedigree-based selection (BLUP) in data from a selection experiment that applied both methods side by side. The impact of traditional selection and GS on the overall genome variation as well as the overlap between regions selected by GS and the genomic regions predicted to affect the traits were assessed. The impact of selection on genome variation was assessed by measuring changes in allele frequencies that allowed the identification of regions in the genome where changes must be due to selection. These frequency changes were shown to be larger than what could be expected from random fluctuations, indicating that selection is really affecting the allele frequencies and that this effect is stronger in GS compared with BLUP. Next, concordance was tested between the selected regions and regions that affect the traits, as detected by a genome-wide association study. Results showed a low concordance overall between the associated regions and the selected regions. However, markers in associated regions did show larger changes in allele frequencies compared with the average changes across the genome. The selection experiment was performed using a medium density of DNA markers (60K). I subsequently explored the potential benefits of whole-genome sequence data for GS by comparing prediction accuracy from imputed sequence data with the accuracy obtained from the 60K genotypes. Before sequencing, the selection of key animals that should be sequenced to maximize imputation accuracy was assessed with the original 60K genotypes. The accuracy of genotype imputation from lower density panels using a small number of selected key animals as reference was compared with a scenario where random animals were used as the reference population. Even with a very small number of animals as reference, reasonable imputation accuracy could be obtained. Moreover, selecting key animals as reference considerably improved imputation accuracy of rare alleles compared with a set of random reference animals. While imputation from a small reference set was successful, imputation to whole-genome sequence data hardly improved genomic prediction accuracy compared with the predictions based on 60K genotypes. Using only those markers from the whole-genome sequence that are more likely to affect the phenotype was expected to remove noise from the data, but resulted in slightly lower prediction accuracy compared with the complete genome sequence. Finally, I evaluated the inclusion of dominance effects besides additive effects in GS models. The proportion of variance due to additive and dominance effects were estimated for egg production and egg quality traits of a purebred line of layers. The proportion of dominance variance to the total phenotypic variance ranged from 0 to 0.05 across traits. Also, the impact of fitting dominance besides additive effects on prediction accuracy was investigated, but was not found to improve accuracy of genomic prediction of breeding values.

    Breeding against infectious diseases in animals
    Rashidi, H. - \ 2016
    Wageningen University. Promotor(en): Johan van Arendonk, co-promotor(en): Herman Mulder; P.K. Mathur. - Wageningen University - ISBN 9789462576452 - 179
    livestock - infectious diseases - animal breeding - selective breeding - disease resistance - tolerance - genetic variation - breeding value - genetic correlation - traits - genomics - animal genetics - vee - infectieziekten - dierveredeling - selectief fokken - ziekteresistentie - tolerantie - genetische variatie - fokwaarde - genetische correlatie - kenmerken - genomica - diergenetica

    Infectious diseases in farm animals are of major concern because of animal welfare, production costs, and public health. Farms undergo huge economic losses due to infectious disease. The costs of infections in farm animals are mainly due to production losses, treatment of infected animals, and disease control strategies. Control strategies, however, are not always successful. Selective breeding for the animals that can mount a defence against infection could therefore be a promising approach. Defensive ability of an animal has two main mechanisms: resistance (ability to control the pathogen burden) and tolerance (ability to maintain performance when pathogen burden increases). When it is difficult to distinguish between resistance and tolerance, defensive ability is measured as resilience that is the ability to maintain performance during a disease outbreak regardless of pathogen burden. Studies have focused on the genetics of resistance and resilience with little known about the genetics of tolerance and its relationship with resistance and resilience. The objectives of this thesis were to: 1) estimate the genetic variation in resistance, tolerance, and resilience to infection in order to assess the amenability of these traits for selective breeding in farm animals, 2) estimate the genetic correlation between resistance, tolerance and resilience and 3) detect genomic regions associated with resistance, tolerance, and resilience.

    In chapter 2, we studied the variation among sows in response to porcine reproductive and respiratory syndrome (PRRS). First a statistical method was developed to detect PRRS outbreaks based on reproduction records of sows. The method showed a high sensitivity (78%) for disease phases. Then the variation of sows in response to PRRS was quantified using 2 models on the traits number of piglets born alive (NBA) and number of piglets born dead (LOSS): 1) bivariate model considering the trait in healthy and disease phases as different traits, and 2) reaction norm model modelling the response of sows as a linear regression of the trait on herd-year-week estimates of NBA. Trait correlations between healthy and disease phases deviated from unity (0.57±0.13 – 0.87±0.18). The repeatabilities ranged from 0.07±0.027 to 0.16±0.005. The reaction norm model had higher predictive ability in disease phase compared to the bivariate model.

    In chapter 3 we studied 1) the genetic variation in resistance and tolerance of sheep to gastrointestinal nematode infection and 2) the genetic correlation between resistance and tolerance. Sire models on faecal nematode egg count (FEC), IgA, and pepsinogen were used to study the genetic variation in resistance. Heritability for resistance traits ranged from 0.19±0.10 to 0.59±0.20. A random regression model was used to study the reaction norm of sheep body weight on FEC as an estimate of tolerance to nematode infection. We observed a significant genetic variance in tolerance (P<0.05). Finally a bivariate model was used to study the genetic correlation between resistance and tolerance. We observed a negative genetic correlation (-0.63±0.25) between resistance and tolerance.

    In chapter 4, we studied the response to selection in resistance and tolerance when using estimated breeding values for resilience. We used Monte Carlo simulation to generate 100 half-sib families with known breeding values for resistance (pathogen burden) and tolerance. We used selection index theory to predict response to selection for resistance and tolerance: 1) when pathogen burden is known and selection is based on true breeding values for resistance and tolerance and 2) when pathogen burden is unknown and selection is based on estimated breeding values for resilience. Using EBV for resilience in absence of records for pathogen burden resulted in favourable responses in resistance and tolerance to infections, with more emphasis on tolerance than on resistance. However, more genetic gain in resistance and tolerance could be achieved when pathogen burden was known.

    In chapter 5 we studied genomics regions associated with resistance, resilience, and tolerance to PRRS. Resistance was modelled as sire effect on area under the PRRS viremia curve up to 14 days post infection (AUC14). Resilience was modelled as sire effects on daily growth of pigs up to 28 days post infection (ADG28). Tolerance was modelled as the sire effect on the regression of ADG28 on AUC14. We identified a major genomics region on chromosome 4 associated with resistance and resilience to PRRS. We also identified genomics regions on chromosome 1 associated with tolerance to PRRS.

    In the general discussion (chapter 6) I discussed: 1) response to infection as a special case of genotype by environment interaction, 2) random regression model as a statistical tool for studying response to disease, 3) advantages and requirements of random regression models, and 4) selective breeding of farm animals for resistance, tolerance, and resilience to infections. I concluded that random regression is a powerful approach to estimate response to infection in animals. If the adequate amount of data is available random regression model could estimate breeding values of animals more accurately compared to other models. I also concluded that before including resistance and tolerance into breeding programs, breeders should make sure about the added values of including these traits on genetic progress. Selective breeding for resilience could be a pragmatic approach to simultaneously improve resistance and tolerance.

    Multi-population genomic prediction
    Wientjes, Y.C.J. - \ 2016
    Wageningen University. Promotor(en): Roel Veerkamp; Mario Calus. - Wageningen : Wageningen University - ISBN 9789462576193 - 267
    cum laude - dairy cattle - genomics - prediction - quantitative trait loci - genetic improvement - breeding value - selective breeding - animal breeding - animal genetics - melkvee - genomica - voorspelling - loci voor kwantitatief kenmerk - genetische verbetering - fokwaarde - selectief fokken - dierveredeling - diergenetica
    Cum laude graduation
    Exploiting genomic information on purebred and crossbred pigs
    Hidalgo, A.M. - \ 2015
    Wageningen University. Promotor(en): Martien Groenen, co-promotor(en): D.J. de Koning; John Bastiaansen. - Wageningen : Wageningen University - ISBN 9789462576018 - 202
    varkens - genomica - kruising - inteeltlijnen - genetische verbetering - fokwaarde - drachtigheidsperiode - androstenon - prestatieniveau - varkensfokkerij - diergenetica - pigs - genomics - crossbreds - inbred lines - genetic improvement - breeding value - gestation period - androstenone - performance - pig breeding - animal genetics
    Textbook animal breeding : animal breeding andgenetics for BSc students
    Oldenbroek, Kor ; Waaij, Liesbeth van der - \ 2014
    Wageningen : Centre for Genetic Resources and Animal Breeding and Genomics Group, Wageningen University and Research Centre - 311
    dierveredeling - selectief fokken - huisdieren - agrarisch onderwijs - diergenetica - lesmaterialen - hoger onderwijs - animal breeding - selective breeding - domestic animals - agricultural education - animal genetics - teaching materials - higher education
    This textbook contains teaching material on animal breeding and genetics for BSc students. The text book started as an initiative of the Dutch Universities for Applied (Agricultural) Sciences. The textbook is made available by the Animal Breeding and Genomics Centre (ABGC) of Wageningen UR (University and Research Centre).
    Voerstrategie voor vleesvarkens in relatie tot genetische aanleg en geboortegewicht
    Peet-Schwering, C.M.C. van der; Troquet, L.M.P. ; Binnendijk, G.P. ; Vogelzang, R.H. ; Knol, E.F. - \ 2014
    Wageningen : Wageningen UR Livestock Research (Rapport / Wageningen UR Livestock Research 816) - 37
    diervoedering - varkens - varkenshouderij - biggen - diergenetica - geboortegewicht - economische zoölogie - varkensvlees - agrarische bedrijfsvoering - animal feeding - pigs - pig farming - piglets - animal genetics - birth weight - economic zoology - pigmeat - farm management
    At Swine Innovation Centre Sterksel the effects of genetic background, birth weight and feeding strategy on the performance and financial results of piglets and growing and finishing pigs were investigated. The results are described in this report.
    Fokkerij geeft antwoord op vragen maatschappij
    Greef, K.H. de; Hiemstra, S.J. ; Kool, E. - \ 2014
    V-focus 2014 (2014)1. - ISSN 1574-1575 - p. 28 - 29.
    varkenshouderij - dierenwelzijn - varkens - dierveredeling - staartbijten - varkensfokkerij - diergenetica - genotypische variatie - duurzame veehouderij - pig farming - animal welfare - pigs - animal breeding - tail biting - pig breeding - animal genetics - genetic variance - sustainable animal husbandry
    De fokkerij kan een belangrijke bijdrage leveren aan het oplossen van een probleem als berengeur en het begrijpen van staartbijten. Naast deze twee maatschappelijke vraagstukken zijn er veel meer vragen waarop het samenwerkingsverband Breed4Food antwoord wil geven. Dit artikel beschrijft doorbraken, die Breed- 4Food wil realiseren in de varkensfokkerij om daarmee bij te dragen aan een economisch en maatschappelijk duurzame houderij.
    Consensus methods for breeding low methane emitting : Breeding ruminants that emit less methane - development of consensus methods for measurements of methane (white paper)
    Pickering, N.K. ; Haas, Y. de; Basarab, J. ; Cammack, K. ; Hayes, B. ; Hegarty, R. ; Lassen, J. ; McEwan, J. ; Miller, S. ; Pinares-Patino, C. ; Shackell, G. ; Vercoe, P. ; Oddy, Hutton - \ 2013
    ASGGN - 57
    animal breeding - selection - animal genetics - genomics - methane - sheep - cattle - agriculture and environment - dierveredeling - selectie - diergenetica - genomica - methaan - schapen - rundvee - landbouw en milieu
    This report was prepared by a working group of the Animal Selection, Genetics and Genomics Network (ASGGN) of the Global Research Alliance for reducing greenhouse gases from agriculture. It is a summary of published and yet to be published work. The purpose is to evaluate methods that are potentially useful for measuring CH4 emissions in individual animals so as to estimate genetic parameters and subsequently screen animals for use in selective breeding programs including its use in the development of genomic selection.
    Opmerkelijke genen in de schapenfokkerij
    Slaghuis, H. ; Oldenbroek, J.K. - \ 2013
    Zeldzaam huisdier 2013 (2013)4. - ISSN 0929-905X - p. 10 - 12.
    schapenrassen - schapen - genen - natuurlijke selectie - diergenetica - genetische bronnen van diersoorten - sheep breeds - sheep - genes - natural selection - animal genetics - animal genetic resources
    Eén van de criteria voor het bewaren van rassen is de aanwezigheid van een uniek kenmerk in dat ras. Vaak is dat een unieke kleuraftekening, maar soms zijn dat ook kenmerken die een duidelijk effect hebben op het functioneren. Wereldwijd zijn er bij een aantal schapenrassen dit soort opmerkelijke genen gevonden.
    De vererving van het witrikpatroon en de variatie daaarin
    Schoon, M. ; Oldenbroek, J.K. ; Oijen, M. van - \ 2013
    Zeldzaam huisdier 38 (2013)3. - ISSN 0929-905X - p. 18 - 19.
    witrik - rundveerassen - zeldzame rassen - diergenetica - dierveredeling - kleur - overerving - coloursides white back - cattle breeds - rare breeds - animal genetics - animal breeding - colour - inheritance
    In een afstudeeropdracht voor van Hall Larenstein is de vererving van de witrikkleur bij runderen bestudeerd en is de vraag beantwoord waarom er zoveel kleurpatronen zijn binnen deze kleurslag.
    Snow shoes and sandals? : genetic aspects of heat stress sensitivity and sow reproduction
    Bloemhof, S. - \ 2013
    Wageningen University. Promotor(en): Johan van Arendonk; I. Misztal, co-promotor(en): E.F. Knol; Liesbeth van der Waaij. - S.l. : s.n. - ISBN 9789461735881 - 173
    zeugen - warmtestress - diergenetica - gevoeligheid - geslachtelijke voortplanting - voortplantingsvermogen - kritische temperatuur - hittetolerantie - selectief fokken - genetische correlatie - veredelingsprogramma's - varkensfokkerij - sows - heat stress - animal genetics - sensitivity - sexual reproduction - reproductive performance - critical temperature - heat tolerance - selective breeding - genetic correlation - breeding programmes - pig breeding

    Globally the average size of pig herds are increasing and amount of labour spent per sow / finisher pig is decreasing. These changes require sows which need less management interventions. In addition to easier manageable sows modern genotypes will also need to be more adaptable considering that global temperatures are expected to increase and pork production is partially moving to warmer climates. The end result is that commercial pigs nowadays will potentially face more heat stress challenges during their productive lives.

    In this thesis, a model was developed which was used to estimate upper critical temperatures for sows’ reproductive performance. Additionally the possibility to breed for reduced heat tolerance of sows was investigated. Therefore heritability for the random regression slope of farrowing rate against increasing temperature at day of insemination (= heat tolerance) and the genetic correlation between farrowing rate and heat tolerance was estimated.Commercial production pigs are crossbreds farmed all over the world. In contrast, selection is practiced mainly in temperate climates, in nucleus herds using purebred pigs. The success of genetic selection depends on how much genetic progress is realized in crossbred pigs. Within this thesis these genetic correlations for farrowing rate between purebreds and crossbreds were estimated.

    Sow productivity depends on a number of related traits, such as ovulation rate, the number of litters per sow per year, the number of weaned piglets per sow per year, and the length of productive live. Traditionally pig breeding programs have improved sow productivity by increasing number weaned piglets per sow per year. To improve herd-level litters per sow per year a new trait was proposed called problem free sow production by parity, which incorporates the traits interval weaning first insemination, non-return rate, farrowing rate, and selection for next parity. Heritability of problem free sow production and genetic correlations with other sow production traits were estimated.

    The main conclusion of this thesis was that it is possible to select for improved heat resistance in addition to improved commercial production levels in commercial pigs. However, genetic correlation between production in temperate and hot climates is high. This high correlation implies that, within-line, pigs with the best performance in a hot climate will be the best in temperate climate too. Most important for the success of a pig breeding program is to define appropriate breeding goals which are based on the environment(s) that market pigs are expected to perform in. The overall data collection for the genetic evaluation needs to be done in those specific environments and this will favour pigs which are able to produce over more than one specific environment.

    Swimming Physiology of Fish: Towards Using Exercise to Farm a Fit Fish in Sustainable Aquaculture
    Palstra, A.P. ; Planas, J.V. - \ 2013
    Heidelberg [etc.] : Springer - ISBN 9783642310485 - 429
    dierfysiologie - vissen - wildbeheer - zwemmen - genomica - diergenetica - gedragswetenschappen - ontogenie - aquacultuur - animal physiology - fishes - wildlife management - swimming - genomics - animal genetics - behavioural sciences - ontogeny - aquaculture
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