Transport is a critical factor affecting swine welfare in modern U.S. commercial pork production. Broad temperature ranges encountered during transport can challenge pig welfare and have been shown to increase the number of dead and down pigs following transport. To better characterize the thermal environments experienced by trailered pigs during hot, mild, and cold weather, The National Pork Board commissioned this observational study to evaluate the thermal environment during commercial pig transport when the trailer environment was managed according to a set of industry guidelines. The overall goal of this observational study was to identify weather conditions and micro-climates within the trailer that created thermal challenges for the pigs.

In this study, 84 temperature sensors were placed along trailer cross-sections in six evenly distributed zones within the transport trailer to measure air temperature experienced by the pigs. Six relative humidity and temperature probes and a surface IR thermometer were installed on the central ceiling of each zone to measure a representative moist-air state point for each compartment and the temperature of the pigs’ backs. Eighteen to twenty-four floor temperature sensors were placed onto the trailer floor prior to each monitoring trip to measure trailer floor/bedding temperature.

Transport thermal environment data from forty-three monitoring trips were collected from May 2012 to February 2013, with trailer management conducted by the commercial hauler and corresponding to the National Pork Board Transport Quality Assurance (TQA) guidelines (NPB, 2008). The thermal environment profile within the trailer was used to evaluate the thermal conditions to which pigs were exposed over a broad range of outside conditions encountered (7 to 100 °F; -14 to 38°C).
Results showed that for outside temperature below 20°F (-7°C) and above 90°F (32°C), pigs experienced extreme thermal conditions inside the trailer with current TQA guidelines. For many scenarios with extreme conditions observed, the worst-case scenario could have been improved with greater uniformity in trailer ventilation and/or application of cooling method.

The ventilation patterns inside the trailer did not follow the same trend for all monitoring trips, revealing potential to manipulate ventilation patterns with trailer management strategies. This approach for improving the thermal extremes needs further exploration, but may offer a strategy to avoid the most extreme cold microclimates within the trailer.

The effectiveness of fans and misting for cooling the pigs was critically impacted by the location and coverage areas of the spray nozzles and fans, resulting in limited benefit observed for these methods in this study. When outside temperature ranged from 50 to 69°F (10 to 20°C), trailer environment was within acceptable thermal limits without misting the pigs, demonstrating no need for this recommendation in TQA.

During cold weather, frozen floor conditions were observed, with floor temperature as cold as -4 °F (-20°C) in some areas of the trailer. No evidence indicated that bedding depth had a measurable effect on the thermal comfort of the pigs, and might increase the severity and likelihood for the pigs to be loaded onto freezing or frozen bedding in extreme cold weather.

Our data revealed no critical problems with boarding level recommendations based on current TQA guidelines, but indicated that industry guidelines could be modified to offer greater flexibility for drivers for boarding and bedding within the less extreme outdoor temperatures.

Additionally, observations revealed rapid temperature increases when the trailer came to a stop for several minutes. The study also revealed the need for development of a weather safety index appropriate for pigs which could be applied to pigs during transport.

More detailed discussion over this summary and potential changes to the current TQA guidelines is included near the end of this report.