Dynamics Of Hematology, Immunology, And Nasopharyngeal Microbiome Related To Naturally Occurring Bovine Respiratory Disease In Commercial Stocker Cattle

Stocker cattle experience several adverse conditions including abrupt weaning, transportation, castration, commingling, and become susceptible to bovine respiratory disease (BRD). Bovine respiratory disease is the most expensive disease in beef production and is mainly diagnosed by visual observations. Combining diagnostic aids such as thoracic ultrasound, hematology, and immunology was found to provide better accuracy in BRD diagnosis in feedlot cattle compared to their individual use. Limited studies on BRD progression in stocker cattle bolstered the necessity of the project. Data presented in this dissertation focused on understanding the changes in hematological and immunological parameters as well as the nasopharyngeal (NP) microbiome in naturally occurring BRD in stocker cattle. All data presented in this dissertation was collected on 40 commercially owned stocker calves. Chapter 2 focuses on the hematological and immunological changes that occurred in this population from day 0 (arrival) to day 21, which is the highest risk period for BRD onset. The cumulative incidence of BRD was 40%. Results from the studies showed that hematological parameters are non-specific to measure BRD progression. Significant interaction between treatment numbers and day was observed for haptoglobin concentration. Temporal variation in cytokine concentration (IL-1β, IL-8, and TNF-α) was observed, and higher sampling frequency was suggested to better identify patterns related to the onset of clinical disease. Chapter 3 focuses on measuring the temporal variation of NP microbiome in stocker cattle. Results identified Firmicutes, Proteobacteria, Actinobacteriota, Bacteroidota, and Verrucomicrobiota as the top phylum and Mycoplasma as the top genus. The relative abundance of different phyla differed temporally among healthy calves. At arrival, the relative abundance of Lactobacillus and Saccharococcus was higher and decreased over time. Mycoplasma abundance had significant interaction between treatment numbers and sampling day. Pasteurella and Bacillus differed based on the number of treatments. Data obtained through these studies related to hematology, immunology, and NP microbiome will be helpful to describe naturally occurring BRD progression in stocker cattle. Future research should focus on determining the feasibility of haptoglobin as a biomarker in BRD. Additionally, variability in NP microbiome based on sex, age, diet, breed, and specific antibiotics needs to be studied.