A study performed by the Kentucky Equine Research Staff assessed air exchange rates in trailers with various ventilation port configurations and with differing numbers of horses being transported. The researched looked at air movement and temperature in several areas of the trailer, and also quantified the effect of vehicle speed, window openings and number of horses on air exchange.
How the Study was Performed
Ten different locations were used to measure the air exchange rate, both with and without horses present, by use of tracer gas concentration decay tests. The exchange rate was determined at three different speeds to simulate driving in town, on rural roads and on limited-access highways.
Three different arrangements of ventilation were also tested. These include the windows and forward-facing roof vents closed, the windows open and roof vents closed, and the windows and roof vents open. For this study, four mature geldings (three Thoroughbreds and one Standardbred) were used. All these horses had been transported many times and were familiar with the particular trailer used in the study.
The trailer was a four-horse, slant-load, Gooseneck model with a rear window, a window at the head and tail of each horse, and a forward-facing roof vent over each horse’s head. All openings had a total area of 1.05 square meters (11.86 square feet). The horses were positioned so that their head angled toward the driver’s side of the vehicle. Stalls were numbered accordingly one through four beginning at the front of the trailer, and were divided by moveable partitions attached to the driver’s side.
The method used to determine air flow was tracer gas concentration decay measurement because it is the only analysis appropriate for air spaces with multiple inlets and outlets. To determine exchange rate, only relative changes in concentration are required. Every ten seconds, concentration was measured using infrared sensors spaced at various locations inside and outside the trailer. Carbon dioxide, which was the tracer gas, was injected into the trailer until the concentration reached equilibrium at the upper end of the sensor range and dilution was measured as fresh air entered the trailer.
Using a sensor that determined both temperature and relative humidity, the outside air temperature was measured. Thermocouples were used to measure the temperature in the trailer, which were located with the carbon dioxide probes. At the beginning of each round of measurements, the trailer was allowed to achieve target speed and remain at that speed for two to three minutes to allow air flow patterns to develop. To promote dispersion and mixing within the trailer, carbon dioxide was injected throughout this period. Concentrations above 5000 ppm (the suggested human exposure limit), were avoided. When the calibration level of the sensors were reached, injection was stopped and the concentration was allowed to decay to equilibrium while the vehicle maintained a constant speed.
The Results of the Study
No valid data was collected at the lowest speed that simulated town driving when horses were in the trailer. The sensors exceeded calibration limits with the injection of carbon dioxide, exhalations of the horses and low rates of air exchanged combined at this speed.
As expected, increasing speed usually caused more air exchange, and air exchange was also enhanced when all windows and vents were open. Air exchange varied by location when horses were in the trailer, with the lowest exchange rates found in the stall nearest to the front of the trailer.
The average air exchange rates were only about half those recommended for stabled horses, even at the highest speed with all windows and vents open. While the outside temperature never exceeded 82°F during the study, heat stress conditions (defined as air temperature exceeding 86°F) were observed inside the trailer. Horses in the stall nearest the front of the trailer routinely showed more sweating than those in other locations.
What Can We Take from This Study?
Based on an analysis of the data results, the trailer used in this study was determined to be under ventilated.
A similar independent study showed less variation of air exchange by location when upper rear trailer doors were removed. Ways to provide better air exchange and minimize heat stress of transported animals include:
- increasing window size
- opening upper rear doors
- removing upper rear doors
When comparing trailer models prior to purchase, an important aspect to look for maximum ventilation. In this study, data was collected for only two conditions, empty trailer or trailer holding four horses. Air exchange rate was lower in front stalls than in rear stalls when four horses were transported. One way to possibly avoid overheating of multiple horses during transport is by placing the smallest or leanest horse in the first stall.
While it is safe to assume that increased air exchange minimizes the buildup of dust and mold spores in trailer air, drafts due to increased speed can still blow particles of dust, hay and straw through the trailer. Placing fly masks on animals being transported can assist with keeping the dust and airborne materials from causing eye injuries.
It is important to keep your livestock from getting overheated during travel days in your trailer, especially as the summer time is upon us. Gooseneck Trailers offers different ventilation systems to best fit your livestock trailer. Contact Gooseneck Trailers with the link below for more information!