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Effects of Transdermal Flunixin Meglumine on Pain Biomarkers at Dehorning
The objective of this study was to evaluate the analgesic effects of topical flunixin meglumine (Finadyne Transdermal; MDS Animal Health, UK) when given at the time of dehorning on pain biomarkers. Twenty four weaned male Holstein calves, ages 6 to 8 weeks of age were enrolled into the study. The calves were randomly assigned to one of three treatment groups of: 1) topical flunixin and dehorn (DH-FLU); 2) topical flunixin and sham dehorn (SHAM-FLU); and 3) placebo and dehorn (DH-PLBO). Treated calves had tropical flunixin meglumine applied at the label dose of 3.33 mg/kg concurrently with dehorning. Dehorning was performed using an electrocautery dehorner applied to the horn for 10 seconds. Sham dehorning was completed using a cold dehorner applied to the horn for 10 seconds. Biomarker parameters collected and analyzed included: infrared thermography (IRT), mechanical nociception threshold (MNT), plasma cortisol, and Substance P. There were no differences in temperatures detected for the IRT measurements of the medial canthus of the eye, dehorning site and adjacent skin for the DH groups. Mean control point MNT measurements at 49 hours were 3.14 kgF, 3.46 kgF and 1.43 kgF for the DH-FLU, Sham-FLU and DH-PLBO groups respectively (P = 0.0001). No other differences of MNT were detected between groups for the other test sites and time points. Plasma cortisol reached peak concentration at 20 minutes post dehorning for the DH-FLU and DH-PLBO groups and 10 minutes for SHAM-FLU group. Peak plasma cortisol concentrations were 32.0 ng/ml, 12.7 ng/ml, and 28.8 ng/ml for the DH-FLU, SHAM-FLU and DH-PLBO groups respectively. Cortisol concentrations were statistically lower for the DH-FLU group at 90 minutes post dehorning compared to the SHAM-FLU and DH-FLU group (P = 0.04). Substance P concentrations at 4 hours post dehorning were 27.81 pg/ml, 27.08 pg/ml, and 30.36 pg/ml for the DH-FLU, SHAM-FLU, and DH-PLBO groups respectively (P = 0.8496). No differences in Substance P concentrations between groups were detected for all time points. In conclusion, topical flunixin meglumine given at the time of dehorning did not provide substantial analgesia based on the pain biomarkers investigated.
Keywords: Dehorning, analgesia, flunixin meglumine