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Title: Thermal environment in a four-horse slant-load trailer

item Purswell, Joseph - Jody
item GATES, R - University Of Illinois
item LAWRENCE, L - University Of Kentucky
item DAVIS, J - Mississippi State University

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/24/2010
Publication Date: 12/30/2010
Citation: Purswell, J.L., Gates, R.S., Lawrence, L.M., Davis, J.D. 2010. Thermal environment in a four-horse slant-load trailer. Transactions of the ASABE. 53(6):1885-1894.

Interpretive Summary: Horses are transported more than most livestock and other domestic animals. Ensuring suitable thermal conditions and air quality is of prime concern to maintain animal health status and alleviate thermal discomfort. Air temperature, radiant temperature, and relative humidity were measured at ten locations within a four-horse slant-load trailer under nine different combinations of travel speed and vent configuration. Differences between inside and outside conditions were affected by both travel speed and vent configuration, with the highway travel speed (60 mph) with all windows and vents open providing the lowest temperature increases during warm weather. However, temperature differences exceeded those recommended for horse housing, and confirmed that trailers of this design are under-ventilated. A thermal model was employed to determine the required ventilation rate to maintain conditions within the recommendations for horse housing; the model indicated that ventilation rates should be increased by 35% to maintain conditions within 3 C of outside temperature.

Technical Abstract: Little information has been published describing thermal conditions in horse trailers while in transit. Dry bulb temperature (Tdb), globe temperature (Tg), and relative humidity (RH) were measured in ten locations within a fully enclosed four-horse slant-load trailer with and without animals to assess the thermal environment during transport as influenced by vehicle speed and vent configuration. Wet bulb globe temperature (WBGT) was calculated to assess thermal comfort. Interior-exterior temperature differences were analyzed to account for effects of changing weather conditions. Temperature differences between the interior of the trailer and ambient conditions for Tdb ranged from 5.1°C to 9.5°C, dew point (Tdp) ranged from 4.4°C to 13°C, and WBGT ranged from 2.9°C to 7.9°C. Temperature differences decreased with increasing vehicle speed and open vent area and increased with animals present. Heat stress conditions are likely to occur in horse trailers of similar design given their limited ventilation and the temperature increases measured in this study, and warrant improvements in trailer design to increase ventilation.