*2.1. General Information*

This paper summarizes results from a multi-year commissioned study that involved three to five monitoring trips every month for over a year, with each monitoring covering a complete transport trip for market-weight pigs (from loading pigs at a pig barn to finish unloading at an abattoir) in the Midwestern U.S. The objective of the commissioned study was to evaluate effects of industry implementation of trailer managemen<sup>t</sup> (bedding, boarding, and wetting) on trailer interior thermal environment as outlined in the TQA handbook [20]. Therefore, the field measurement was dictated by the outdoor conditions and the specifications of the TQA guidelines. The detailed information of the trailer description, instrumentation of the monitoring system, analysis of pig surface temperature, pig mortality on arrival, effects of trailer bedding depth and boarding percentage on pig skin surface temperature during cold and mild weather conditions are found in the companion paper that characterizes the observations over all weather conditions [15].

#### *2.2. Trailer Description and Measurement System Overview*

A newly fabricated commercial double-decked pot-belly livestock transport trailer designated for pig transport was used in this study (Figure 1). While this style trailer can be converted to a three-deck configuration for transporting weaned piglets, the trailer in this study was used with only two decks for market pigs throughout the study. The trailer was equipped with three hinged gates on each deck and a loading ramp deployed at the bottom rear. Four 25 × 25 cm nose vents are located in the front corners of the trailer (two to a side, as shown in Figure 1). All nose vents are completely open during hot weather and completely covered during winter. The trailer was divided into six animal zones, numbered from 1 to 3 on the top and 4 to 6 on the bottom deck, from the front to the back. A monitoring system was developed to measure thermal conditions inside each of the six trailer zones. A detailed trailer schematic with zone compartmentalization and monitoring system can be accessed from the companion paper from the same study [15]. The monitoring system in each zone consisted of 14 thermistors (Model 10M5351, Honeywell Parts, Phoenix, AZ, USA), for a total of 84 thermistors in the trailer, to measure pig-level air temperature and one centrally-located temperature and relative humidity (RH) probe (Vaisala INTERCAP HMP60, Vaisala, Vantaa, Finland) per zone to capture the center-zone condition near the ceiling. A weather station was installed outside of the trailer to capture the outside temperature (Tout) and RH. Data was recorded every minute.

**Figure 1.** Trailer used for trailer environment monitoring in this field study. The same trailer was instrumented and utilized for all monitoring of trailer interior environment during all commercial market-weight pigs transport throughout this study.

#### *2.3. Procedures during a Commercial Pig Transport Trip*

During a typical commercial pig transport trip in the Midwestern U.S., the trip generally proceeds in the following segments: (1) arriving at a commercial pig barn and loading market-weight pigs, where variable waiting time at the barn can occur; (2) departing for road transport, and the duration of the transport varies greatly due to distance between scattered barn locations and the abattoir; (3) arriving at the abattoir and unloading the pigs, where waiting time may likely occur due to uncertain processing schedules at the abattoir. During summer conditions, additional cooling procedures may be additional to the trip, based on availability at the barn or abattoir. As for this study, we observed two combinations that can be flexibly available to the trailer operator, including applying misting to the trailer interior at the pig barn, and applying misting at the abattoir, with or without accessing air flows compensated by external fans.

#### *2.4. Summary of Field-Monitoring Trips*

A total of 40 commercial transport trips for market-weight pigs were successfully monitored with the instrumentation system from May 2012 to February 2013, covering a wide distribution of outdoor conditions, including extreme temperature events [14]. The same trailer was used, and the same driver was responsible for operating and configuring the trailer and managed the animals during all monitoring trips to avoid discrepancy in trailer design, management, and animal handling. All trailer procedures, including misting the interior trailer, bedding and boarding arrangements followed TQA general recommendations. Truck average velocity was approximately the same across all monitoring trips. All trips were conducted with full loading capacity (170–175 market-weight pigs at 127–136 kg each). With a 79.2 m<sup>2</sup> total trailer floor space, the loading density was 275–300 kg/m2.

These 40 trips were categorized into five thermal categories based on average Tout recorded during each trip. Table 1 summarizes the thermal categories and the number of trips included in each category. Analyses of trailer managemen<sup>t</sup> were broken into cold weather analysis that included trips in *Very Cold* and *Cold* categories, and hot weather analysis that included trips in *Mild*, *Warm*, and *Very Hot* categories.


**Table 1.** Summary of field-monitoring trips completed with thermal categories based on average outside air temperature range recorded during each trip.

\* For the *Very Cold* category, one trip experienced thermistor failures and was excluded from this table and analysis involving pig-level air temperatures.

#### *2.5. Evaluation of Hot Weather Trips*
