In the United States, about 0.7% of commercial pigs become injured, non-ambulatory 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 United States greater death losses are recorded during June to September when ambient temperatures typically exceed 68 degrees Farhenheit. The risk of death for market-weight pigs during transport, for example, may be 1.4 times higher at 85 to 92 F than at 54 to 79 F.
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 over-heated, 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 over-heating and heat stress.
Adaptations to minimize risk of heat stress 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 freely available on-line to anyone. MSU Extension highly recommends that all pork producers who transport pigs complete TQA on-line 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:
- Schedule transportation during early morning or evenings to avoid the hottest part of the day.
- Open nose vents and unplug most or all ventilation slots.
- Take care not to add to pig stress at loading; load in proper group size (e.g., 3-5 at a time for finishers), use sorting boards only (if possible), avoid loud noises, loading ramp should have 20 degrees or less incline angle. Do not load pigs showing obvious signs of fatigue such as open mouth breathing, blotchy skin, muscle tremors, reluctance to move, stiffness.
- Make sure pig density is within the recommended range; 300-pound pigs should have at least 5-6 square feet of floor space.
- Reduce bedding to 1-4 50 lb. bags per load in hot weather; use woodchips instead of straw on hot days as straw retains more heat.
- Keep loading and unloading times to a minimum; this helps reduce heat build-up that can occur rapidly on a stationary truck.
- If ambient temperatures exceed 80 F spray pigs using large drops of water (not a fine mist) for 5 to 10 minutes during or after loading to improve evaporative cooling. Do not over-spray, as this can create a sauna effect on the truck.
- For most trucks transporting pigs, proper ventilation, especially under hot/humid conditions, requires that the truck be moving. Do not stop for periods longer than required to fill a gas tank.
- Make sure the destination is expecting you and is prepared to off-load or keep your pigs moving once you arrive.
- Have a back-up plan in case re-routing is required, or if an accident or prolonged traffic stoppage occurs.
- If you have to stop due to breakdown or traffic conditions, move the trailer in an area that provides shade and breeze. Wet the pigs to keep them cool. If water is unavailable and heat conditions are extreme consider contacting the local fire department to wet the pigs with water from a fire truck.