Browsing by Subject "Inzucht"

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    Entwicklung und Etablierung eines innovativen Zuchtwertschätzverfahrens für lokale Rinderrassen in Baden-Württemberg
    (2020) Kohl, Sebastian; Herold, Pera
    Over the last decades, cattle breeding schemes that used truncation selection provoked high inbreeding rates and were perceived increasingly critical. Reasons are the inefficient conversion of genetic variance in genetic gain and an increased risk of inbreeding depression (Falconer and Mackay, 1996; Woolliams et al., 2015a). A solution was found by Meuwissen (1997) by introducing Optimum Contribution Selection (OCS). OCS facilitates the maximization of genetic gain meanwhile restricting inbreeding rates to predefined levels. Wellmann et al. (2012) extended the existing OCS approach by two components: Migrant contributions and native genetic variance of the breed under observation. The resulting advanced OCS (aOCS) facilitates the implementation in regional breeds that have been crossbred with commercial breeds for upgrading reasons. Basic research has already been carried out (Wang et al., 2017a; b). The objectives of the underlying project were (I) a comparison of OCS approaches to be implemented in Vorderwald cattle by underlying population parameters following Hartwig et al. (2013). (II) A feasibility study to give empirical prove of the applicability of the chosen OCS approach in Vorderwald cattle. The main focus was on the costs of implementing OCS in Vorderwald cattle. These were contrasted with the benefits. (III) The development of strategies to implement an OCS approach in connection to the breeding value estimation at the Landesamt für Geoinformation und Landentwicklung Baden-Württemberg. The development of routine applications was paramount here. (IV) The development of a suitable breeding scheme that fits a proportion of 50 % natural mating in the actual Vorderwald population. Chapter 1 is an opinion article about financial, structural and social obstacles that impede the implementation of OCS in real breeding schemes. This chapter is mainly related to small scale cooperative breeding schemes of Germany, since this is a common organizational structure of regional breeds. Chapter 2 is a feasibility study. On basis of the identified obstacles of Chapter 1, a concrete and easy to implement breeding scheme will be developed. A stochastic simulation will be carried out, to reveal flaws in the developed breeding scheme and aOCS approach. Additionally, results of the stochastic simulation are directly comparable to real data. Chapter 3 is an extension of the feasibility study of Chapter 2 and proofs the feasibility of the developed breeding scheme under actual conditions of the Vorderwald cattle breed. Migrant contributions to the Vorderwald cattle breed reached 61 % in 2014. Thus, the aOCS approach was modified to test for possibilities of reducing this level. The thesis will end with a general discussion. Recommendations will be given, how to implement the developed breeding scheme of Chapter 2 in Vorderwald cattle and comparable breeds.
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    Improvements of the doubled haploid technology in maize
    (2019) Molenaar, Willem; Melchinger, Albrecht E.
    The in vivo doubled haploid (DH) technology in maize carries many advantages over traditional line development by recurrent selfing and has played an integral role in numerous breeding programs since the early 21st century. A bottleneck in the DH technology is still the success rate of chromosome doubling treatment, which has a strong influence on the costs of DH production. Currently, only a minority (~10%) of treated D0 haploid plants result in DH lines. Improvement in the chromosome doubling step of DH production would not only make DH lines cheaper, but could also change the optimum allocation of resources in hybrid breeding. In addition, the development of treatments using alternative doubling agents to colchicine, which is toxic to humans, would improve worker safety and simplify waste disposal issues for developing countries to benefit from the DH technology. Initiating such developments is the goal of this thesis. In a first step, we evaluated anti-mitotic herbicides with different modes of action as alternatives to colchicine for reducing the toxicity of chromosome-doubling treatment and for potentially increasing the success rates. In a series of experiments, we evaluated anti-mitotic herbicides with different modes of action in different concentrations and combinations. Based on the results of the initial experiments, we chose a specific concentration of amiprophos-methyl for evaluation in combination with varying concentrations of pronamide in a further experiment. This revealed the optimal concentration of pronamide in combination with the chosen concentration of amiprophos-methyl. However, this less-toxic treatment showed slightly lower success rates and slightly higher costs per DH line as compared to the standard colchicine treatment. In a second step after evaluating anti-mitotic herbicides for seedling treatment, we evaluated gaseous treatments using nitrous oxide (N2O), an anti-mitotic gas, in varying concentrations and combinations with air and pure oxygen. In two years of evaluation, we found an N2O treatment which had similar success rates as colchicine. The major benefit of such treatment is that this gas can simply be released into the atmosphere, eliminating the difficulty of proper chemical waste disposal, which is difficult to secure in developing countries. The only requirement is a treatment chamber, in contrast to the laboratory facilities required for handling colchicine. In a third step, we evaluated the potential of spontaneous chromosome doubling (SCD) as an alternative to chemical treatment-based chromosome doubling. Although previous studies found significant genetic variation and high heritability for SCD, a classical quantitative genetic analysis, elucidating the type of gene action governing this trait, and a selection experiment for improving SCD was missing in the literature. We found a predominance of additive genetic effects compared to epistatic effects, and a large selection gain after three cycles of recurrent selection for SCD to levels far beyond those reached by standard colchicine treatment. This indicates the great potential of SCD to improve the DH technology. The approximately ten-fold increase in spontaneous chromosome doubling rate (SDR) reached in our recurrent selection experiment marks a paradigm shift in the chromosome doubling step of DH production in maize. DH production efficiency can be greatly increased by the vast improvement in SDR, and production can be further simplified to enable even higher throughput. Instead of chromosome doubling treatment, which involves much handling of seedlings, haploid seeds from germplasm with a high innate ability to produce seed set without chemical treatment can be simply seeded in the DH nursery, eliminating the most costly production steps. Thus, this thesis has provided new opportunities to increase worker safety and reduce toxic waste in DH production, and further provided a proof of concept for genetic improvement of spontaneous chromosome doubling, which has great prospects for increasing the efficiency of DH production in maize.
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    Pedigreeanalysen zur Beschreibung der populations- und quantitativgenetischen Situation von baden-württembergischen Lokalrinderrassen
    (2014) Hartwig, Sonja; Bennewitz, Jörn
    The challenge of a conservation breeding program is to solve a conflict of goals: genetic variability and genetic autonomy should be maintained, and on time a certain amount of breeding progress has to be realized to ensure the ability to compete. The aim of the present study was to analyse the situation concerning the targets mentioned above for traditional cattle breeds of Baden-Württemberg. Furthermore, methods for the consolidation and development of these breeds should be reconsidered. In chapter 1 the organisation of a breeding program for small cattle breeds is discussed. The challenge of such a program is the conservation of agrobiodiversity, culture and traditions and the progress of traditional local breeds. Number and extend of these breeds declined due to the increasing popularity of high-yielding breeds. Additionally, some of the local breeds are used in different branches of production compared to their original usage. Breeding programs have to be fitted. The establishment of individual adapted breeding methods is required for a sophisticated solution of the conflict mentioned above. Federal support is requested. Nowadays the implementation of genomic selection is not yet practicable for small breeds. But future opportunities should be analysed. The establishment of performance tests concerning breed specific product and efforts is demanded to improve these characteristics. In the following genetic variability of Vorderwald, Hinterwald and Limpurg cattle was examined. In chapter 2 for each breed two reference populations were defined that enable to observe the development over the years. Animals within the reference population comply with restrictions concerning racial origin and completeness of pedigree. Effective population size and the effective number of founders, and ancestors were estimated. The interpretation of the results was done with regard to the history of the breeds. The absolute population size of Vorderwald cattle is the biggest one. The number of Hinterwald cattle is intermediate; Limpurg cattle have the smallest population size. Whereas the management of Hinterwald cattle seemed to maintain genetic variability, the management of Vorderwald cattle was not that target-orientated. With an effective population size greater than 100 there is enough genetic variability within Vorderwald and Hinterwald. In contrast the values of Limpurg cattle are too low. Besides genetic variability, genetic autonomy and breeding progress are the targets of a conservation breeding program. Cross-breeding was carried out to mitigate the risk of inbreeding depression and to improve the performance of local breeds. However, breeding activities for local breeds were not as intensive and target oriented as for popular high yielding breeds. While the gap between the performance of high-yielding and local breeds increase, genetic autonomy of local breeds declined due to migrant influences. Chapter 3 examined the importance of migrant breed influences for the realization of breeding progress of beef traits of Vorderwald and Hinterwald cattle. The results show that there is a high amount of migrant contributions and their effects on performance are substantial for most traits. Breeding values adjusted for the effects of the migrant breeds showed little genetic trend for beef traits. The subject of chapter 4 is the development of milk yield and the associated migrant influences. Yield deviations for milk, fat, and protein content were analysed. Migrant contributions to Vorderwald cattle were high and even rose in the latest past. All the effects of foreign breeds were positive and in most cases highly significant. Most influential breed was Montbéliard. The influences of migrant breeds were substantial for the development of milk performance. However, the trend of milk yield traits for both breeds was positive even without foreign breeds’ influences. In comparison the number of analysed Hinterwald cows was small due to the reason that just a few Hinterwald husbandries take part at the official milk performance recording. Migrant breed contributions were moderate and nearly constant over the time. The most influential migrant breed was the Vorderwald cattle. The development of milk yield shows a flat trend. Influences of migrant breeds were low. The thesis ends with a general discussion.