Clinical signs of stress in finisher pigs transported to market in the summer

A study conducted in 2001 in Ontario found that of 4,760,213 market weight pigs shipped to packing plants, 7969 died prior to being processed at the plant. Of those that died, 15% were classified as “subject” pigs when they were loaded into the truck.¹ A subject pig is one that appears abnormal for any of a variety of reasons. Pigs shipped in the summer months were twice as likely to die in-transit compared to pigs shipped during other months of the year. The objectives of this study were to describe the numbers of subject pigs and pigs dying intransit and the factors associated with these during the summer. Specifically, we recorded reasons for subject pig classification, clinical signs of stress as pigs were being unloaded, temperatures at the time of unloading, time spent waiting at the packing plant prior to unloading and the relationship between these variables and in-transit loss.

Materials and methods

This observational study included a weekly visit to the three largest packing plants in Ontario during July to September of 2003. Data were collected on 46,331 pigs from 250 trucks and detailed observations were made on 7351 individual pigs as they were unloaded at the plant. Specifically, every fifth pig unloaded for a maximum of 30 pigs per truck was scored for stumbling, panting, squealing, tail injury, and scratched skin. Time of arrival of trucks, wait time prior to unloading, number of pigs per truck and the number of subject and dead pigs on each truck was recorded. The reasons for subject classification, the locations where subject classification occurred and the locations on the trucks where pigs were found dead were recorded. Hourly dry temperature data was purchased from the government and merged with the other data to match the hour when pigs were unloaded. Poisson regression was used to determine the associations between panting, death and subject classifications, temperature at the time of arrival and waiting times at the packers.

Results and discussion

On average 0.27% of pigs were classified as subject. Of the 0.07% pigs that died in-transit, 34% were identified as subject prior to death. Subject classification occurred 6.1%, 30.4%, and 63.4% of the time at the producers, assembly/dispatch yard, and packing plant respectively.

The reasons for subject classification were as follows: pigs showing severe signs of heat stress (fatigued) (48.0%), lame (44.9%), prolapse (6.3%), intact males (3.1%), severe bruises (2.4%), head tilt (1.6%) and tail bitten (1.6%). In total, 7.8% of these pigs had more than one reason for the subject classification. Of the 7351 pigs observed 11.6% stumbled or fell, 5.4% panted, 4.5% squealed, 1.2% had injured (bitten) tails and 59.8% had scratches.

There were 38 pigs that died on the 250 observed trucks. The locations on the trucks where pigs were found dead were as follows: 46% bottom deck, 3% front middle deck, 15% back middle deck, 9% front top deck, 21% center top deck and 6% back top deck. Knowledge of the location on trucks where pigs are more likely to experience heat stress or die from heat stress may be used to alter stocking densities or implement cooling mechanisms in these areas.

During heat stress, pigs thermoregulate by panting and if their body temperature continues to rise they collapse and may die due to cardiovascular failure.¹ Trucks with at least one dead pig were 2.0 times more likely to have panting pigs than trucks without dead pigs (P < 0.0001). Similarly, panting pigs were 2.2 times more likely on trucks with fatigued pigs than on trucks without fatigued pigs (P < 0.0001).

Trucks waited to unload for an average of 49 minutes with a range of 2 to 198 minutes. There was no association between the time waiting to unload at the packersand the risk of pigs panting. However, as the waiting time increased by 30 minutes, the risk of dying and the risk of being a fatigued subject pig increased by 2.2 and 2.3 times respectively (P < 0.0001). The outside temperature when the pigs arrived at the packers averaged 25°C and ranged from 19 to 31°C. As the temperature on arrival at the packers increased by 10°C increments, the risk of panting, dying or being a fatigued subject pig increased 2.3, 26.7 and 26.2 times respectively (P < 0.0001). Previous research on pig transport trailers in Ontario during the summer showed that when stopped, trailer temperature increased on average by 5.6°C. It took 56 minutes for the truck to reach its maximum temperature after the stop. The increase in temperature of the trailer while it was stopped ranged from 0°C to 25°C.¹ Thus, as time waiting to unload at the packers increased, the temperature within the truck would have increased. This rise in temperature may be responsible for the correlation between time waiting in the yard and the risk of death or being a fatigued subject pig.

Heat stress, as indicated by counting panting pigs, was a predictor of subject classification and death during transport. Shipping pigs during the cooler hours of the day, implementing cooling mechanisms such as sprinkler systems (as observed at 2 of the 3 plants) and efforts to decrease wait times prior to unloading may help reduce loss due to heat stress and improve swine welfare.

Acknowledgements

The authors greatly appreciate the contributions of the cooperating packers and truckers and Karen Richardson for her assistance with data collection.

References

^1. Haley, C. 2005. The factors associated with transport loss of market weight swine in Ontario. PhD Thesis, University of Guelph.

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Clinical signs of stress in finisher pigs transported to market in the summer

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