Retrospective analysis of relationships between pro-inflammatory, hematology, and metabolic variables, and mortality following a bovine respiratory disease challenge in weaned calves

Authors: Sanchez, Nicole; Broadway, Paul; Carroll, Jeffery - Jeff Carroll

Submitted to: Frontiers in Immunology
Publication Type: Abstract Only
Publication Acceptance Date: 2/7/2018
Publication Date: 8/31/2018
Citation: Sanchez, N.C., Broadway, P.R., Carroll, J.A. 2018. Retrospective analysis of relationships between pro-inflammatory, hematology, and metabolic variables, and mortality following a bovine respiratory disease challenge in weaned calves. Joint XII Congress of the Latin American Association of Immunology and XXIII Congress of the Mexican Society of Immunology meeting, May 14-18, 2018, Cancun, Mexico. Frontiers ISBN: 978-2-88945-511-9; doi: 10.3389/978-2-88945-511-9; Pp. 1007-1008.
DOI: https://doi.org/10.3389/978-2-88945-511-9

Interpretive Summary:

Technical Abstract: Respiratory disease is the number one illness affecting the cattle industry, resulting in an estimated $2 billion in losses per year. The Livestock Issues Research Unit has utilized a combined viral-bacterial respiratory challenge model in order to study the pathogenesis of the disease. In a recent study, there was uncharacteristically high mortality in response to the challenge. Therefore, an analysis was conducted to determine whether any of the physiological, immunological, or metabolic parameters measured would be predictive of calf death in response to a controlled respiratory disease challenge. Thirty-one crossbred beef calves [n = 16 castrated males (steers) and 15 intact females (heifers)] were acquired and transported to the Livestock Issues Research Unit’s Liberty Farm facility near Lubbock, Texas, USA. Calves were selected based on uniform phenotype characteristics and body weight, and no clinical signs of illness nor treatment history. Additionally, calves were balanced by Bovine Herpesvirus-1 (BHV-1) titers measured 2 weeks prior to the initiation of the study. All calves were previously vaccinated thrice with a combination 5-way respiratory modified-live vaccine without a bactarin in accordance with the farm processing protocol where the calves were acquired. Additionally, calves were fitted with indwelling rectal or vaginal temperature monitoring devices to allow monitoring of body temperature continuously at 5-min intervals prior to relocation to the research facility. The following day, calves were challenged intranasally with 1 x 10^8 PFU of BHV-1 in 1-mL PBS in each nostril using an atomizer. The calves were then allowed to rest in covered outdoor pens for 72 h. The calves were then processed through a working facility where they were fitted with indwelling jugular vein catheters and challenged intratracheally with Mannheimia haemolytica (MH) in log-phase growth at a dose of 1.27 x 10^7 CFU in PBS. Relative to the MH challenge, two whole blood samples were collected at -72 (time of BHV-1 challenge), 0 (time of MH challenge), 2, 4, 6, 8, 12, 24, 36, 48, 60, 72 and 168 h. Serum was isolated from one sample for determination of glucose, non-esterified fatty acids, serum urea nitrogen, interleukin-4 (IL-4), interleukin-6 (IL-6) and interferon-' (IFN-g) concentrations. The second blood sample was used to determine complete blood counts (red blood cells, hemoglobin, hematocrit, platelets, white blood cells, neutrophils, lymphocytes, monocytes, eosinophils and basophils) in real time using a ProCyte Dx Hematology Analyzer (IDEXX, Westbrook, Maine, USA). Seventy-two hours following administration of MH, catheters and temperature monitoring devices were removed, and all calves were treated with a florfenicol and placed back in the covered outside dirt pens for 4 days. An additional blood sample was collected on d 7 (168 h post-MH challenge) before calves were shipped to a research feedlot approximately 160 km away. Of the 31 calves on study, 10 calves (6 steers and 4 heifers) died in response to the challenge. Three calves died at approximately 48 (1 calf) and 72 h (2 calves) relative to MH challenge. The remaining seven calves died 15 days or more following the MH challenge. To determine what factors may be indicative of calf death, stepwise logistics regression was performed on variables measured (cytokines, metabolites, hematology and body temperature) immediately prior to BHV-1 administration (-72 h) and at the peak temperature response following MH challenge (12 h). Results from the analysis found that of the 17 variables measured, only IL-4 (P = 0.08) was considered predictive of calf death prior to BHV-1 administration. Additionally, IL-6 concentration (P = 0.08) at the time of peak febrile response was the only variable predictive of subsequent calf death. Further Pearson correlation analysis at the two time