In the U.S., about 0.7% of commercial pigs become injured, nonambulatory or die while being transported.

Results from several studies (some included thousands of truckloads of pigs) sponsored by the pork industry indicate that multiple factors contribute to injury and death loss of pigs during transportation. Factors include how animals are handled before and during loading, loading density, quality of road, driving method, distance driven, ambient temperature, ventilation, whether animals were sprayed with water (to help cool in hot weather), and how long the truck sat still after loading and before unloading at its destination.

Among these factors, ambient temperature appears to be more important across multiple studies, even spanning continents. In the U.S., greater death losses are recorded from June to September when ambient temperatures typically exceed 68 degrees F. The risk of death for market-weight pigs during transport, for example, may be 1.4 times higher at 85 to 92 degrees than at 54 to 79 degrees.

Why pigs are prone to heat stress

Pigs possess few sweat glands and are unable to generate enough skin moisture to allow evaporative cooling (reduction in body temperature resulting from evaporation of sweat from the pig’s surface). In addition, pig lungs are small for the size of their body, limiting the effectiveness of panting. They still pant when overheated, but its effectiveness is limited.

These factors, together with the thick layer of fat that forms a layer of insultation under their skin further preventing heat loss through the body surface, leave pigs highly susceptible to overheating and heat stress.

Adaptations during transportation

Thorough and up-to-date information on how to minimize risks associated with elevated temperature, heat stress and other weather-related events during transportation can be found at Transport Quality Assurance (TQA) Handbook, Version 8.0, which is free online to anyone. 

MSU Extension recommends that all pork producers who transport pigs complete TQA online training, which covers this material in detail. Summarized here are a few of the simple, cost-effective measures pig haulers should consider whether they are hauling one large pig or 400 small pigs, especially during late-spring and summer months when elevated temperatures and humidity persist:

Benjamin, Rozeboom, Rossman and Thompson write for MSU Extension.