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Exploring Complete Blood Count to Improve Disease Resilience in Pigs

  • Author / Creator
    Bai, Xuechun
  • Disease resilience is defined as an animal’s ability to maintain a high level of performance in the face of disease challenges caused by multiple pathogens, as is often the case in commercial pig farms. Therefore, disease resilience is anticipated to be critical to the profitability of the pig industry. However, it is difficult to make genetic improvement for disease resilience because it is not expressed in the purebred nucleus herds housed in high-health environments where the selection of elite breeding animals occurs. In addition, disease resilience to the challenge of multiple pathogens in commercial pig production systems is a complex trait that is hard and expensive to measure. Complete blood count (CBC) is a relatively inexpensive, robust, and routinely used blood test in veterinary laboratories to evaluate overall health and detect disorders. Exploring CBC traits for genomic selection could be a promising approach to address the above issues of making genetic improvement of disease resilience. Two strategies have been proposed for genomic selection of disease resilience based on CBC traits. The first strategy is to explore indicator CBC traits of disease resilience that can be directly collected from the nucleus herds, and the second strategy is to explore practical CBC phenotypes of disease resilience in commercial farms when the disease challenge is present for genomic selection. Therefore, the overall objective of this thesis was to explore the opportunity to use CBC traits collected under the high-health nucleus farms condition and a model of the polymicrobial challenge faced in commercial farms to improve disease resilience in pigs. A wean-to-finish natural disease challenge model (NDCM) consisting of a high-health quarantine barn and a polymicrobial challenge barn was established for the project. Three sets of blood samples were collected to determine CBC: the first was collected from high-health pigs in the quarantine barn, a second (termed Blood 3) and third (Blood 4) were collected in the challenge barn at 2- and 6-week after exposure to the polymicrobial challenge. Firstly, most CBC traits in Blood 1, 3, and 4 were heritable, with heritability estimates ranging from 0.06 ± 0.04 to 0.53 ± 0.05. A few CBC traits in Blood 3 and 4 were found to be genetically correlated with the resilience traits of grow-to-finish growth rate (GFGR) and antimicrobial and anti-inflammatory treatment incidence (treatment rate, TR) (-0.38 ± 0.18 to -0.82 ± 0.47; 0.50 ± 0.23 to 0.89 ± 0.26). No significant genetic correlation was identified for CBC in Blood 1 with GFGR or TR. Then, genome-wide association studies (GWAS) of CBC traits and gene expression analysis of animals with divergent CBC traits in response to the challenge were used to investigate the genetic control of disease resilience. GWAS found that CBC traits were polygenic traits controlled by a large number of genes with small effects. Gene expression analysis suggested that up-regulation of genes involved in apoptosis might associate with the decreased lymphocyte concentration from Blood 1 to Blood 3 and resulted in lower disease resilience. Lastly, moderate genomic prediction accuracies (0.12 ± 0.04 to 0.28 ± 0.03) were found for three CBC traits under disease (lymphocyte concentration in Blood 3, neutrophil concentration and red blood cell distribution width in Blood 4) that had moderate to high genetic correlations (−0.38 ± 0.18 to 0.89 ± 0.26) with TR. Genomic selection on these three CBC traits may lead to a desirable decrease in TR to reduce antimicrobial use and antimicrobial resistance in the swine industry. Overall, the results reported in this thesis suggest that genomic selection of CBC traits collected from high-health nucleus farms cannot improve disease resilience regarding the resilience traits of GFGR and TR. However, CBC traits collected in commercial farms when the disease challenge is present can be used as practical disease resilience phenotypes and have the potential to be used to help develop a selection index for nucleus animals to make genetic improvement for disease resilience.

  • Subjects / Keywords
  • Graduation date
    Fall 2021
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.