Browsing by Author "Gunasegaram Narayana, Saranya"

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    Genetics and genomics of bovine mastitis resistance
    (2024-01-10) Gunasegaram Narayana, Saranya; Barkema, Herman; Schenkel, Flavio; Miglior, Filippo; Kastalic, John; Orsel, karin
    Mastitis, a multifactorial infectious disease primarily caused by bacteria, remains a major economic challenge for the dairy cattle industry, despite decades of extensive research. To combat mastitis effectively, breeding for enhanced mastitis resistance through genetic selection, in combination with improved management strategies, offers a promising alternative. This thesis delves into the genetic and genomic aspects of mastitis, exploring the following key areas: 1) Genetic analysis of subclinical mastitis (SCM): By employing both linear and threshold models, the research presented in Chapter 2 investigated the genetic basis of SCM in early lactating heifers. Despite the relatively low heritability for six different SCM traits, this analysis revealed a notable genetic variation among sires, suggesting the possibility of long-term genetic selection to enhance heifer mastitis resistance. 2) Genetics of pathogen-specific intramammary infections (IMI): In Chapter 3, the genetic variation of overall and pathogen-specific IMI in nonclinical primiparous and multiparous cows was explored. The results demonstrated substantial exploitable genetic variability among daughters of sires for overall IMI and six IMI pathogen group traits. Furthermore, results indicated that the selection for lower somatic cell score (SCS) may not uniformly improve resistance to IMI from every pathogen group. 3) Underlying genetic architecture of mastitis resistance: Through a systematic review of genome-wide association studies and gene prioritization analysis, the research presented in Chapter 4 aimed to decipher the genetic architecture of mastitis resistance in dairy cattle. This comprehensive study identified numerous unique genes and quantitative trait loci, emphasizing the polygenic nature of mastitis, with many of the prioritized genes linked to immune response. 4) Genomic Copy Number Variants (CNVs) and SCS: The investigation in Chapter 5 uncovered three significant CNVs associated with SCS in Holstein cows, including four novel findings. Annotation analysis again identified numerous genes linked to immune response. 5) Genomic predictions of mastitis-related traits: Chapter 6 explored genomic prediction of mastitis-related traits in early first lactation of dairy cows, utilizing a single-step genomic approach. This approach demonstrated a substantial increase in validation and theoretical reliabilities for genomic prediction of genomic estimated breeding value of young animals compared to traditional pedigree-based prediction. In summary, this thesis highlights the genetic potential for enhancing mastitis resistance in dairy cattle, shedding light on various aspects of genetic and genomic influences on mastitis-associated traits. These findings provide valuable insights for the development of improved breeding strategies in the dairy industry.