**4. Conclusions**

Variation in the six zones within a commercial transport trailer over the course of a year were tested for lack of uniformity against different factors depending on outdoor weather conditions. For 20 trips conducted during *Mild*, *Warm* and *Very Hot* conditions, no significant variation was observed in temperature rise or average THI between the six trailer zones. Ventilation through the trailer was sufficient to limit temperature rise due to sensible and latent heat contributions by the pigs. Misting during loading the trailer with pigs showed modest benefit to cool the trailer interior temperature to less than outside temperature, however, misting did not improve the average THI and created short term heat stress conditions as measured by maximum THI in the trailer, pushing the thermal environment to a potentially dangerous condition for at least some portion of the transport segment. After transport, fans with or without misting reduced temperature rise in some zones of the trailer but the benefits were not uniform.

For 20 *Cold* and *Very Cold* weather trips, the trailer interior thermal environment was not uniform, with the front top and bottom zones being the warmest, indicating less ventilation in these areas, which is in line with results from animal transport assessments for pigs and other species. Boarding/bedding combinations changed ventilation rates but was generally inconsistent with respect to variation in temperature, and boarding position had no measurable effect on ventilation pattern or rate. Unlike the warmer weather situation with full ventilation, a partially boarded trailer reduced the ventilation rate and resulted in a temperature gradient from the rear towards the front, conforming to the air inlet and outlet locations, respectively. The potential implications of reduced ventilation would be a susceptibility to poorer air quality and potentially challenging thermal environment for the pigs, which have significant consequences for pig welfare during cold weather transport.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2076-2615/8/11/203/s1, Animation A1: Animation of a complete commercial pig transport trip during very hot weather condition (1). Animation A2: Animation of a complete commercial pig transport trip during very hot weather condition (2). Animation A3: Animation of a complete commercial pig transport trip during warm weather condition. Animation A4: Animation of a complete commercial pig transport trip during mild weather condition. Animation A5: Animation of a complete commercial pig transport trip during very cold weather condition.

**Author Contributions:** Conceptualization, Y.X., R.S.G. and A.R.G.-M.; Methodology, A.R.G.-M., R.S.G. and Y.X.; Software, Y.X.; Validation, Y.X.; Data Analysis, Y.X., R.S.G. and A.R.G.-M.; Writing-Original Draft Preparation, Y.X. and R.S.G.; Writing-Review and Editing, Y.X., R.S.G. and A.R.G.-M.; Visualization, Y.X.; Supervision, A.R.G.-M.; Project Administration, A.R.G.-M.; Funding Acquisition, A.R.G.-M.

**Funding:** This study was funded by the National Pork Board. Grant Number: NPB # 10-175.

**Acknowledgments:** The authors thank Reich Trucking, and special thanks to Rick Reich for their collaboration. The authors also acknowledge the efforts of personnel from the University of Illinois.

**Conflicts of Interest:** The authors declare no conflict of interest.
