Browsing by Subject "Breeding strategies"

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    Breeding strategies for Sahiwal cattle genetic resources in Kenya
    (2011) Ilatsia, Evans D.; Valle Zárate, Anne
    The Sahiwal breed is an important cattle genetic resource in the tropics where it is vital for subsistence and economic development among various communities. In Kenya a breeding and conservation programme has been in existence for over 45 years with the ascertains of its relevance in light of the producers? production aims and breeding goals still left pending. Moreover, there have been no systematic efforts undertaken to evaluate the suitability of the existing breeding programme or to examine how competitive it is compared to other alternative programmes in terms of genetic and economic merit. This thesis focused on understanding the breeding strategies for improvement of Sahiwal cattle genetic resources in Kenya. Specific objectives were; 1) to critically examine the existing breeding and conservation programmes for Sahiwal cattle genetic resources in the tropics focussing mainly on the strengths and weaknesses in Pakistan, India and Kenya as the core regions of development, 2) to understand the production conditions under which Sahiwal cattle genetic resources are raised, determine producers production aims and assess the relative importance of breeding goals and production challenges, 3) to identify and define the roles of various stakeholder institutions that are crucial in the realisation of a promising and sustainable Sahiwal cattle breeding programme, 4) to identify based on genetic and economic merits the optimal breeding programme for Sahiwal cattle genetic resources by evaluating the current and alternative breeding programmes, and 5) to analyse and discuss organisational options for implementation of promising breeding and conversion programmes. The results from the literature review study show that most studies on Sahiwal cattle genetic resources in the tropics have mainly concentrated on evaluating their performance levels with only a few published reports describing other breed characteristics. The Sahiwal breed is utilised for dairy and beef production under smallholder dairy pastoral extensive and ranching production systems both as purebreds or crossbreds. The necessary components to strengthen the breeding programme such as performance recording genetic evaluation and AI facilities exist albeit at different degree. Breeding and conservation efforts benefit from the technical and financial support from government research institutions, which also provide incentives to enhance participation in the programmes. However, breeding goals are rather informal and only defined in terms of high production levels with functional traits largely ignored. Field data analysis revealed that Sahiwal genetic resources were mainly kept for domestic milk production and for revenue generation through sales of milk and live animals. To a limited extent they were kept for breeding and also for multiple objectives that included insurance against risks and social functions. Production aims were influenced to varying extents by various household and farmer characteristics. Sahiwal cattle and their crosses were generally perceived to be better with respect to productive traits and fertility traits when compared to the EAZ. However, the EAZ was rated higher with respect to adaptation traits. The breeding objective traits of primary importance were high milk yield and big body size, good reproductive efficiency and relatively good adaptation to local production conditions. Performance and functional traits are important breeding goals that play a major role in fulfilling the multiple production objectives. This forms the basis for the optimisation of a breeding programme for sustainable utilisation to meet the needs of Sahiwal cattle producers. All the breeding programmes evaluated in this study showed positive genetic and economic gains, however, the difference was only in the margins of these benefits. Given the small population of the Sahiwal breed, an open-nucleus breeding programme is economically and genetically optimal because it will allow for efficient utilisation of the existing genetic base by allowing participation of more diverse pastoral born sires in the nucleus. The CNCROSS will continue to play an important role of facilitating the exploitation of trade-offs that exist between the Sahiwal and the EAZ with regard to production and adaption, as well as an intermediate phase in the up-grading programme. However, the full benefits of the open-nucleus breeding programme can only be realised in the presence of proper logistical organisation to facilitate exchange of breeding bulls between the pastoral herds and the nucleus farms and ensure equitable distribution. Co-operation between producers and relevant stakeholder institutions is necessary to ensure the requisite structures for implementation and sustainable execution of the breeding programme.
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    Optimum strategies to implement genomic selection in hybrid breeding
    (2022) Marulanda Martinez, Jose Joaquin; Melchinger, Albrecht E.
    To satisfy the rising demand for more agricultural production, a boost in the annual expected selection gain (ΔGa) of traits such as grain yield and especially yield stability has to be rapidly achieved. Hybrid breeding has contributed to a notable increment in performance for numerous allogamous species and has been proposed as a way to match the increased demand for autogamous cereals such as rice, wheat, and barley. An additional tool to increase the rate of annual selection gain is genomic selection (GS), a method to assess the merit of an individual by simultaneously accounting for the effects associated with hundreds to thousands of DNA markers. Successful integration of GS and hybrid breeding should go beyond the study of GS prediction accuracy and focus on the design of breeding strategies, for which GS maximizes ΔGa and optimizes the allocation of resources. The main goal of this thesis was to examine strategies for optimum implementation of GS in hybrid breeding with emphasis on estimation set design to perform GS within biparental populations and on the optimization of hybrid breeding strategies through model calculations. One strategy, GSrapid, with moderate nursery selection, one stage of GS, and one stage of phenotypic selection, reached the greatest ΔGa for single trait selection regardless of the budget, costs, variance components, and accuracy of genomic prediction. GSrapid was also the most efficient strategy for the simultaneous improvement of two traits regardless of the correlation between traits, selection index chosen, and economic weights assigned to each trait. The success of this strategy relies principally on the reduction of breeding cycle length and marginally on the increase in selection intensity. Moving from traditional breeding strategies based on phenotypic selection to strategies using GS for single trait improvement in hybrid breeding could lead not only to increments in ΔGa but also to large savings in the budget. The implementation of nursery selection in breeding strategies boosted the importance of efficient systems for inbred generation accompanied by improvements in the methods of hybrid seed production for experimental tests. When it comes to multiple trait improvement, the choice between optimum and base selection indices had minor impact on the net merit. However, considerable differences for ΔGa of single traits were observed when applying optimum or base indices if the variance components of the traits to be improved differed. The role of the economic weights assigned to each trait was determinant and small variations in the weights led to a remarkable genetic loss in one of the traits. The optimum design of estimation sets to perform GS within biparental populations should be based on phenotypic data, rather than molecular marker data. This finding poses major challenges for GS-based strategies aiming to select the best new inbreds within second cycle breeding populations, as breeding cycle length might not be reduced. Then, the ES design to optimize GS within biparental populations would have a defined application on the exploitation of within-family variation by increasing selection intensity in biparental populations with the largest potential of producing high-performing inbreds. Based on the results of this thesis, future challenges for the optimum implementation of GS in hybrid breeding strategies include (i) reductions in breeding cycle length and increments in selection intensity by refinements of DH technology or implementation of speed breeding, (ii) improvements in the methods for hybrid seed production, facilitating the reallocation of resources to the production of more candidates tested during the breeding cycle, and (iii) precise estimation of economic weights, reflecting the importance of the traits for breeding programs and farmers, and maximizing long term ΔGa for the most relevant traits.