First phase of a Canadian study provides insight into the transport stressors and their impact on carcass quality.

Data collected during the first phase of a four-year study of hog transportation in Canada should lead to improved handling practices, fewer injuries and less carcass bruising.

The study, coordinated through the Prairie Swine Centre at the University of Saskatchewan, analyzed data collected during summer and winter hauling conditions in two parts of the country.

The Quebec research team looked at short hauls of 1½ hours, utilizing two types of livestock trailers — a double-deck and a tri-axle potbelly. Both were specifically designed for hauling pigs.

The Saskatchewan team analyzed data from eight-hour hauls, utilizing a tandem-axle potbelly commonly used for both pigs and cattle.

In both instances, teams collected data from the time pigs were loaded through their arrival at the plant and subsequent slaughter, including examining carcasses.

Researchers recorded the physical condition of the pigs, the methods used to load them, temperature, relative humidity and hauling distance, all of which play a role in mortality rates and carcass quality, says team leader Harold Gonyou, an ethologist with the Prairie Swine Centre in Saskatoon.

Stress Indicators

Humidity and ambient temperatures inside the various compartments of the trailers were analyzed against metabolic factors, including core body temperatures collected from pigs in each load.

University of Saskatchewan transport specialist Trever Crowe gathered temperature and humidity data from inside the trailer used on eight-hour hauls in both summer and winter. Figures 1 and 2 show compartment temperature variation during a moderately cold winter day (week 2) and very cold winter day (week 4).

Because of timing and logistics, hauls were performed overnight so there was no data gathered during extreme heat in the summer trials. Likewise, winter tests were not performed during extreme cold commonly found in the regions.

Temperatures during the five winter trips ranged from 14 to -18°F. Summer temperatures during the six summer trips ranged from 50 to 59°F.

The pigs are a significant source of heat and moisture, while radiation also affects the temperature inside the trailer, Crowe explains.

Porosity of gates and appropriately placed ventilation holes in the trailer are vital in directing air flow. Tarps or solid panels are installed to restrict flow and help keep animals warmer during cold weather, he says.

“We need to take advantage of pressure differences to try to move the air through the vehicle to cool the animals,” he continues. “If we have an enclosed, moving truck, the air should move from the rear to the front.”

Humidity exacerbates the effects of extreme heat and cold, with the tipping point at 58°F, where humidity has no effect.

Sensors mounted on ceilings of the trailer were naturally closer to the pigs in some compartments than in others, so those differences were factored in when data was analyzed.

Forty-four data buttons were mounted in each trailer, down the midline and along the sides, with temperature and relative humidity recorded once per minute (See Figures 3 and 4).

While moving, the middle and lower decks were warmer than the upper decks. In winter, temperatures at the rear of the trailer tended to be cooler, warmer at the front.

When stopped at the plant, upper deck temperatures became cooler in the front and rear compartments, but warmer in the middle two.

In winter, the upper deck was more humid, while the lower nose and belly compartments were consistently the warmest on the truck, Crowe says.

The experiments showed that heat radiates from the roof to help cool the upper deck in both summer and winter conditions, while higher humidity in those compartments suggests there is less air flow than in the middle deck and potbelly.

Once the truck has stopped, compartments at the center warm up while the front and rear compartments cool down.

Core Body Temperatures

Gonyou's experiments with core body temperatures found that the temperatures and humidity inside the compartments as well as the length of trip affected the levels and types of stress the animals experienced.

Overall, highly stressed animals did not recover well if they were unable to cool down and rest during transport, he notes.

Along with other metabolic factors, the pigs' core body temperatures were measured to see how they reacted at various points of the trip in winter and summer conditions.

Core temperatures were measured at set intervals, including loading, waiting to leave, the first 90 minutes of travel, the last five minutes before arrival, waiting to unload, and the rest period before entering the stunning room.

“The first thing we noticed — once they've departed the farm, in the first 90 minutes, their core body temperature is elevated. I think it's due to the energy expended getting onto the truck,” Gonyou observes. “It's interesting to note that after this long transport …their core body temperature is about what it was back on the farm.”

In the Quebec trial, with only two hours in transit, the pigs' core body temperatures remained high during travel.

Overall, the main effects occurred during loading and travel, with very little difference between compartments. Gonyou says the pigs likely would have struggled more to keep cool, had the summer trials taken place during the heat of the day.

The findings reinforce two key points — pigs expend extra energy during loading and also in winter as they try to keep warm, he says.

“That's an import issue, because if they're generating heat, they're using the energy reserves in their bodies, and that's going to have an effect when we start looking at what's happening at slaughter,” he adds.

Transport Affects Carcasses

Carcass data was collected on 25% of the pigs in the study. Researchers note that weather conditions and travel distance each had different effects on meat quality.

Acute stress caused an increase in pale, soft and exudative (PSE) meat, while extended stress resulted in meat that was dark, firm and dry (DFD), Gonyou explains.

Phases 2 and 3 of the study will utilize data gathered from Phase 1 to find ways of relieving those stressors with the ultimate goal of delivering healthier pigs to slaughter, he says.

Transportation Tips

Researchers offered the following hog loading and transport suggestions:

  • Eliminate electric prods, currently banned in Quebec and at some facilities in the Prairie Provinces;

  • Use compressed-air prods as a viable alternative for encouraging pigs to move forward;

  • Use fans to alter air flow inside trailers;

  • Adjust openings and positions of trailer vents to improve air flow;

  • Insulate trailer compartments that are known to be cooler during winter travel;

  • Sprinkle water on pigs to keep them cool during waiting periods and warmer days; and

  • Switch from tandem- to tri-axle potbellies to reduce the incline of loading ramps, thus, the energy pigs expend during loading.

Across Canada, one-tenth of 1% of slaughter pigs (16,000) are dead on arrival at the plant, with a higher incidence in the summer, Gonyou says. Carcass damage and reduced meat quality renders additional losses.

Phase 2 of the transportation study will look more deeply into key components of stress on the animals, while Phase 3 will look at technologies to reduce those stressors under commercial conditions.

Brenda Kossowan is a freelance writer from Leslieville, Alberta, Canada.