*Article* **Factors Affecting Trailer Thermal Environment Experienced by Market Pigs Transported in the US**

#### **Yijie Xiong \*, Richard S. Gates and Angela R. Green-Miller**

Agricultural and Biological Engineering, University of Illinois at Urbana-Champaign, 1304 W. Pennsylvania Ave, Urbana, IL 61801, USA; rsgates@illinois.edu (R.S.G.); angelag@illinois.edu (A.R.G.-M.)

**\*** Correspondence: yxiong5@illinois.edu; Tel.: +1-217-244-2791

Received: 1 September 2018; Accepted: 6 November 2018; Published: 9 November 2018

**Simple Summary:** Transport conditions can be a challenge for pigs being transported to market. In this study, 40 trips of commercial market pigs transported from the farms to an abattoir were monitored for thermal conditions including temperature and relative humidity in order to better understand thermal variability within the trailer during transport. Variation in thermal environment inside the pig transport trailer was used as an indicator of ventilation pattern during various weather conditions. During cold weather, the front top and bottom zones were warmer than in the rest of the trailer, indicating less ventilation toward the front of the trailer. Conditions were more uniform throughout the trailer for hot temperatures, indicating sufficient ventilation to limit temperature rise. Misting showed the potential to alleviate high temperatures, but resulted in higher THI conditions. No effect of boarding and bedding combination was observed for spatial distribution of trailer interior temperatures.

**Abstract:** Extreme weather conditions challenge pig thermoregulation during transport and are addressed by the National Pork Board (NPB) Transport Quality Assurance® (TQA) program that provides guidelines for trailer boarding, bedding, and misting. These guidelines are widely applied, ye<sup>t</sup> very little is known about the microenvironment within the trailer. In this study, TQA guidelines (V4) were evaluated via extensive thermal environment measurements during transport in order to evaluate spatial variability and implications on ventilation pattern. Effects of trailer managemen<sup>t</sup> strategies including bedding, boarding, and misting were examined and the trailer was monitored for interior temperature rise and THI responses within six separate zones. The trailer thermal environment was not uniformly distributed in the colder trips with the top front and bottom zones were the warmest, indicating these zones had the majority of outlet openings and experienced air with accumulated sensible and latent heat of the pigs. Relatively enhanced thermal environment uniformity was observed during hot trips, suggesting that ventilation patterns and ventilation rate were different for colder vs. warmer weather conditions. Misting applied prior to transport cooled interior air temperature, but also created high THI conditions in some cases. Neither boarding and bedding combinations in the TQA nor boarding position showed impacts on trailer interior temperature rise or spatial distribution of temperature inside the trailer.

**Keywords:** environment; swine; transport quality; temperature; THI; ventilation; bedding; boarding; misting
