Abstract
As a large contributor to morbidity and mortality, bovine respiratory disease (BRD) is a major concern for the feedlot industry, however, the nutritional needs of BRD infected cattle are not understood. Micronutrients, such as Zn and vitamin A, are known to support the immune response through roles in cell signaling, antioxidant capacity and enzyme function. This study aims to characterize the mineral concentrations and gene expression of healthy, non-lesion lung samples (NLL) and lesion lung (LL) of BRD infected cattle. Thirty dairy × beef steers (230 ± 12.1 kg) were inoculated with 10(4) TCID(50) BRSV strain 375 on d 0 followed by 9.3 x 10(9) CFU Mannheimia haemolytica strain D153 on d 7. Necropsies were performed on d -1, 5, 10 and 15 of challenge. Lungs were assigned a gross pathology score (LPath) where 0 = free of lesions, 1 = 1-5% affected (n = 4), 2 = 5-15% affected (n = 11), 3= 15-30% affected (n = 8), 4 = 30-50% affected (n = 3) and 5 = more than 50% affected (n = 4). Samples of LL and NLL were collected at necropsy for mineral (Ca, Cu, Fe, Mn, Mg, P and Zn) concentration and qPCR analysis of genes related to the immune response and Zn and vitamin A metabolism. Data were analyzed using the Mixed procedure in SAS 9.4 (Cary, NC) as a multivariate paired analysis with fixed effects of LPath and tissue (LL vs. NLL) type and their interaction. The slice option was use to determine simple effects of lung pathology score within tissue type. There was a tendency for an LPath × tissue effect (P = 0.08) where Fe concentrations were lesser in LL at lower pathology scores (LL simple P = 0.03) and LL was lesser in comparison to NLL. Lesion lung had greater concentrations of Ca, Mg, Mn and P compared to NLL (Tissue P ≤ 0.02). Zinc concentrations decreased as LPath increased (LPath P = 0.04). LL also tended toward a greater reduction in Zn concentration with increasing LPath (LL simple P = 0.08). Lesion lung had increased expression of SLC39A8 and RALDH2 genes, while RBP4, RXRα, SLC39A1, SLC39A2, SLC30A1 and SLC30A4 decreased (Tissue P ≤ 0.03). Expression of SLC39A1 was lesser in LPath 1, 2, and 4 (LPath P = 0.01). Expression of SLC39A2 was lesser in LPath 4 (LPath P = 0.05). Within LL, SLC39A1 and SLC30A4 expression was lesser in LPath 4 (LL simple P ≤ 0.05). Lung pathology in BRD-infected cattle affects mineral metabolism, especially within LL. Elevated Ca, Mg, Mn and P in LL and a decline in Zn as pathology increases suggests increased nutrient demands in infected tissues, further supported by the change in gene expression.