Browsing by Subject "Phosphorus utilization"

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    Analysis of phosphorus utilization using the host genome and microbiota variability in Japanese quail
    (2021) Vollmar, Solveig Deniece; Bennewitz, Jörn
    Phosphorus (P) is an essential element for growth and performance of avian species. It is predominantly bound as phytic acids and salts (phytate) in plant seeds. Phytases and other phosphatases can harness P by cleaving P groups. Nonruminants have low endogenous phytase activity in the gastrointestinal tract, and thus, the requirement of this element is not met from exclusive plant-based diets. Therefore, mineral P or phytase enzymes are supplemented in poultry feed. Due to the finite quantities of high quality mineral P worldwide, it is of great economic interest. P supplementation is increasingly causing environmental problems. Past studies investigated the P utilization (PU) of different poultry species. They revealed a high phenotypic variation in PU among individuals. Moderate heritabilities indicates that breeding for this trait is in principle possible. The overall aim of this thesis was to gain a deeper understanding of the variability of P utilization in relation to host genetics, ileal microbiota composition and their interaction in the model species Japanese quail. The objective of chapter two was to verify whether variation in PU in quail is a heritable trait conditioned by a few quantitative trait loci (QTL) with detectable effects. For this purpose, individuals were genome-wide genotyped with a 4k SNP chip, and a linkage map was generated. Based on this map, QTL linkage analysis was performed using multimarker regression analysis in a line-crossing model to map QTL for PU. We identified a few QTL regions with significant effects. Among them was a QTL peak at Coturnix japonica chromosome (CJA) 3 for PU. Several genes were found in the region surrounding this peak, which requires further functional gene analysis. Based on these results, we hypothesized that these traits are polygenically determined due to several small QTL effects, which we could not detect significantly. The overlap of the QTL regions indicated linkage of the traits and confirmed their genetic correlations. With the aim of predicting microbiota-related host traits, chapter three examined the composition of the ileum microbiota and differential abundance analysis (DAA). Based on this study, it was shown that a sex-specific influence on microbiota composition exists. The digesta samples of all animals were dominated by five genera, which contributed to more than 70% of the total ileum microbial community. In examining the microbiota composition of each of the 50 animals with the highest and lowest PU, DAA revealed genera significantly associated with PU. In chapter four, we characterized the influence of performance-related gut microbiota to unravel the microbial architecture of the traits evaluated. The aim of this study was to determine whether the variation in PU is partly driven by the microbial community in the ileum. We used microbial mixed linear models to estimate microbiabilities (m^2). This determines the fraction of phenotypic variance that can be explained by the gut microbiota. The estimation of m^2 was 0.15 for PU and was highly significant. It was also highly significant for feed intake, body weight gain and feed per gain. This model was bivariately extended and showed a high microbial correlation of the traits. Based on both results, the ileum microbiota composition plays a substantial role in PU as well as in performance traits, and there is a considerable animal microbiota correlation, showing that the microbiota affects multiple traits. The microbial drivers of this microbial fraction were identified by applying microbiome-wide association studies (MWAS). By back-solving the microbial linear mixed model, we approximated the effect of single OTUs on the phenotypic traits from the microbial model solutions. An MWAS at the genus level uncovered several traits associated with bacterial genera. Subsequently, we assessed whether the microbial community in the ileum is a heritable host trait that can be used for breeding individuals with improved PU. In chapter five we applied QTL analysis using specific genera to examine whether they are linked with genomic SNP markers. These QTL analyses revealed a link between some microbiota species and host genomic regions of chromosomes and SNP markers. By estimating significant heritabilities for some genera, we were able to provide evidence for the hypothesis that the microbial community and microbial features are at least partially related to host genetics. We predicted the animal microbial effects on PU and correlated performance traits by applying microbial best linear unbiased predictions (M-BLUP). In addition, genomic best linear unbiased predictions (G-BLUP) were used to predict the SNP effect for the predicted animal microbial effect. A combination of those two may help to predict genomic breeding values of the microbiota effects for future hologenomic breeding programs.
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    Genomic and microbial analyses of quantitative traits in poultry
    (2023) Haas, Valentin Peter; Bennewitz, Jörn
    Feed and nutrient efficiency will become increasingly important in poultry production in the coming years. In addition to feed efficiency, particular attention is paid to phosphorus (P) in nonruminants. Especially growing animals have a high demand of P but through the low usability of plant-based P sources for nonruminants, mineral P is added to their feeds. Due to worldwide limited mineral P sources, the high environmental impact of P in excretions and high supplementation costs, a better utilization of P from feed components is required. Animals’ P utilization (PU) is known to be influenced by the host genetics and by gastrointestinal microbiota. The overall aim of this thesis was to investigate the relationships between host genetics, gastrointestinal microbiota composition and quantitative traits with the focus on PU and related traits in F2 cross Japanese quail (Coturnix japonica). Japanese quail represent a model species for agriculturally important poultry species. In Chapter one, a genetic linkage map for 4k genome-wide distributed SNPs in the study design was constructed and quantitative trait loci (QTL) linkage mapping for performance as well as bone ash traits using a multi-marker regression approach was conducted. Several genome-wide significant QTL were mapped, and subsequent single marker association analyses were performed to find trait associated marker within the significant QTL regions. The analyses revealed a polygenic nature of the traits with few significant QTL and many undetectable QTL. Some overlapping QTL regions for different traits were found, which agreed with the genetic correlations between the traits. Potential candidate genes within the discovered QTL regions were identified and discussed. Chapter two provided a new perspective on utilization and efficiency traits by incorporating gastrointestinal microbiota and investigated the links between host genetics, gastrointestinal microbiota and quantitative traits. We demonstrated the host genetic influences on parts of the microbial colonization localized in the ileum by estimating heritabilities and mapping QTL regions. From 59 bacterial genera, 24 showed a significant heritability and six genome-wide significant QTL were found. Structural equation models (SEM) were applied to determine causal relationships between the heritable part of the microbiota and efficiency traits. Furthermore, accuracies of different microbial and genomic trait predictions were compared and a hologenomic selection approach was investigated based on the host genome and the heritable part of the ileum microbiota composition. This chapter confirmed the indirect influence of host genetics via the microbiota composition on the quantitative traits. Chapter three further extended the approaches to identify causalities from chapter two. Bayesian learning algorithms were used to discover causal networks. In this approach, microbial diversity was considered as an additional quantitative trait and analyzed jointly with the efficiency traits in order to model and identify their directional relationships. The detected directional relationships were confirmed using SEM and extended to SEM association analyses to separate total SNP effects on a trait into direct or indirect SNP effects mediated by upstream traits. This chapter showed that up to one half of the total SNP effects on a trait are composed of indirect SNP effects via mediating traits. A method for detecting causal relationships between microbial and efficiency traits was established, allowing separation of direct and indirect SNP effects. Chapter four includes an invited review on the major genetic-statistical studies involving the gut microbiota information of nonruminants. The review discussed the analyses conducted in chapter one to three and places the analyses published in these chapters in the context of other statistical approaches. Chapter four completed the microbial genetic approaches published to date and discussed the potential use of microbial information in poultry and pig breeding. The general discussion includes further results not presented in any of the chapters and discusses the general findings across the chapters.