Effect of clenbuterol on tracheal mucociliary transport in horses undergoing simulated long-distance transportation.
Authors: Norton J L, Jackson K, Chen J W, Boston R, Nolen-Walston R D
Journal: Journal of veterinary internal medicine
Summary
Long-distance horse transport is associated with transport pneumonia, a condition linked to compromised tracheal mucociliary clearance (TMCR) when the head is held in a fixed elevated position during confinement. Norton and colleagues investigated whether clenbuterol, a beta-2 agonist known to enhance TMCR, could mitigate this risk using a cross-over study design with six horses subjected to 48-hour simulated transportation whilst treated with either clenbuterol (0.8 µg/kg orally twice daily) or placebo. Both groups experienced significant TMCR reduction following the simulated transport period; however, horses receiving clenbuterol showed half the decline in clearance rate compared with placebo controls (P = .002), suggesting a protective effect. Whilst other inflammatory markers (serum fibrinogen, peripheral eosinophils, tracheal bacterial load, and degenerate neutrophils) changed significantly during transport regardless of treatment, the clenbuterol group demonstrated improved mucociliary function. For practitioners managing horses undergoing long-distance transportation, these findings support the potential value of perioperative clenbuterol administration as a modest but measurable intervention to preserve tracheal clearance mechanisms and potentially reduce transport-related respiratory complications, though the modest effect size indicates it should complement rather than replace other preventive strategies such as optimised head position management and stall design.
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Practical Takeaways
- •Administering clenbuterol (0.8 µg/kg twice daily) starting 12 hours before long-distance transport can significantly reduce respiratory complications by maintaining better mucociliary clearance
- •Even with clenbuterol, fixed elevated head positioning during transport still impairs airway clearance substantially—consider management strategies beyond pharmacotherapy (head position, ventilation, rest periods)
- •This evidence supports prophylactic use of clenbuterol in high-risk transport scenarios, particularly for animals with pre-existing respiratory compromise
Key Findings
- •Tracheal mucociliary clearance rate (TMCR) decreased significantly in both clenbuterol-treated and placebo groups after 48-hour simulated transport (P=0.002 and P=0.03 respectively)
- •Clenbuterol treatment reduced the decline in TMCR by approximately 50% compared to placebo (P=0.002)
- •Serum fibrinogen, peripheral eosinophil count, tracheal bacterial quantification, and degenerate neutrophils increased post-transport in both groups with no treatment effect
- •Clenbuterol provides modest but measurable protection against transport-induced mucociliary clearance impairment in horses