EFFECTS OF ROAD TRANSPORT ON INDEXES OF STRESS IN HORSES

Stress associated with road transport is believed to be a significant contributor to the pathogenesis of post transport respiratory disease in horses. To determine the effects of road transport on pulmonary fun ction, pulmonary aerosol clearance rates were measured in 4 horses 24 h before, and immediately after, 24 h of road transport by delivering aerosolised (99m)technetium-labelled diethylenetriaminepentacetate (Tc -99m-DTPA) to the lungs and monitoring its washout. Each horse was tra nsported twice, once while the trailer was equipped with a leaf-spring suspension-and bias-ply tyres (trailer's original equipment, smooth r ide) and once while the trailer was equipped with a torsion-bar suspen sion and normal pressure radial tyres (rough ride) in order to generat e different ride characteristics. Before transport, blood was drawn fr om each horse for haematology and measurement of serum cortisol concen tration; 24 h rates of hay and water intake and faecal output were rec orded for each horse, Horses were then transported, 2 at a time, over a 128 km circular route of predominantly rural freeways at a constant speed of 72 km/h for 24 h. Horses were rested by stopping the trailer every 3.75 h for 0.25 h. During transport, heart rates (continuous 1 m in averages), rates of hay and water intake and rates of faecal output were measured. Ammonia (NH3) and carbon monoxide (CO) concentrations were measured within the trailer and temperatures (wet bulb [WB], dry bulb [DB] and black globe [BG]) within the trailer were recorded each minute. Immediately after each experiment blood was drawn for haematol ogy and measurement of pulmonary aerosol clearance rates were measured , For control studies, horses were housed in their stalls while heart rates were measured for 24 h. Slopes calculated from the Tc-99m-DTPA c learance curves for pretransport horses were not significantly differe nt from post transport clearance slopes. Pretransport mean Tc-99m-DTPA clearance half-lives (T-50, left lung mean +/- s.d. 41.7 +/- 15.8 min , right lung 44.6 +/- 19.1 min) were not significantly different from post transport T-50 (left lung 53.5 +/- 14.0 min, right lung 52.0 +/- 11.6 min). Heart rates during transport were not affected by suspensio n type or trip order (the horse's first or second transport experiment ) and were not significantly different from stall controls after the f irst 120 min of the experiment. Horses had increased red blood cell co unt, packed cell volume, haemoglobin, plasma protein and cortisol conc entrations, and decreased body weights immediately post transport, ind icating slight dehydration. Water and hay intake rates were significan tly lower during transport than pretransport. Temperatures within the trailer were highest in the mid-afternoon and lowest in the early morn ing hours, but all temperatures measured in the trailer were within th e comfort zone for large homeotherms. Ammonia and CO concentrations in the trailer during the transport period were within acceptable limits for human exposure. However, respirable articulates in the atmosphere were elevated above safe concentrations for human exposure.