Location: Livestock Issues Research
Project Number: 3096-32000-008-15-R
Project Type: Reimbursable Cooperative Agreement
Start Date: Feb 1, 2018
End Date: Dec 14, 2018
The main objective of this project is to determine if Salmonella migration and translocation is greater in immunocompromised calves, and the extent of Salmonella contamination in the harvest process by identifying the points in the harvest process where lymphatic tissue and synovial fluid may contaminate the carcass during fabrication.
Calves will be obtained from a commercial producer in the panhandle of Texas. Weaned calves will be weighed and rectal swabs will be taken to determine if Salmonella is present. A subset of 20 Salmonella-negative calves of the same sex weighing approximately 150 kg will be transported to the UDSA-ARS Livestock Issues Research Unit in Lubbock, TX. Calves will be randomly assigned to either a control group (CON) or an immunosuppressed group (DEX). On day -4, indwelling jugular catheters and rectal temperature recording devices will be inserted in all calves to facilitate intravenous administration of dexamethasone and serial blood collection for analyses, and to record body temperatures at 5-min intervals. Cattle will be individually housed in stanchions in an environmentally controlled facility with enough space for normal standing and lying behaviors. Cattle will have ad libitum access to food and water. Rectal swabs will be collected from each animal upon arrival and each subsequent day during an adaptation period to verify the absence of innately occurring Salmonella. Immunosuppression for the DEX group will be induced by daily repeated intravenous administration of 0.5 mg/kg body weight of dexamethasone (day -3 to 0). Sterile saline will be administered to the CON group using the same protocol. Beginning on day -3, blood samples will be collected from the jugular catheter at 12-h intervals. Whole blood will be collected to determine the complete blood count, including the following: red blood cells, white blood cells, hematocrit, hemoglobin, platelets, neutrophils, lymphocytes, eosinophils, and basophils. Serum will be used to determine interferon gamma (IFN-') concentrations, a pro-inflammatory cytokine. Salmonella antibody titers and haptoglobin will also be determined. Following the three-day immunosuppression, at day 0 all calves will be inoculated with a laboratory strain of Nalidixic acid-resistant Salmonella Typhimurium at 1.0 x 106 CFU via a bottle containing the bacterial culture combined with milk replacer. Beginning on day 0, serial whole blood samples will be collected at 8-h intervals to continue to monitor the immunosuppression of the cattle and assess potential differences in the inflammatory response of all cattle to the Salmonella challenge. Rectal swabs will be collected daily to monitor fecal shedding of the calves inoculated with Salmonella. A visual evaluation of sickness and fecal scoring on a 4-point scale will occur daily by a trained observer. Feed and water disappearance will be recorded daily. Body weights will be recorded at the end of the experimental trial. At 120 hours post-Salmonella challenge, calves will be humanly euthanized using USDA-approved humane harvest procedures. Necropsy will be performed to obtain aseptically collected tissue samples from each calf to determine the presence of the orally inoculated Salmonella strain.