The micro-environment experienced by pigs on the trailer during transport is critical for animal well-being and, potentially, impacts transport losses and, ultimately, pork quality. Environmental conditions on trailers during transport have not been previously established, largely reflecting the difficulty of measuring the appropriate parameters during transportation. The objective of this project was to develop a computer simulation model to predict the environmental conditions on a livestock trailer during transport of harvest-weight pigs under a typical range of climatic conditions. The results of the simulation model were used to develop recommendations for new trailer designs and management of existing trailer designs to provide the optimum environment on the trailer for finishing pigs during transport under the range of weather conditions routinely experienced in the US.
A trailer of typical current design was equipped with instrumentation in all 11 compartments to measure environmental conditions (temperature, relative humidity, air velocity, surface temperature of the inside surfaces of the trailer and of the pig, and carbon dioxide concentrations). Internal trailer, external ambient conditions, and truck speed were measured in all four seasons during journeys from the start of loading at the farm to the end of unloading at the plant under typical transport conditions. These data were used to construct a computer simulation model that predicts the conditions on the trailer for the typical range of weather and transport conditions experienced in the US. Based on the results of the computer model simulation, recommendations for improvements of current trailer designs and of transport management practices were developed.
Major findings and recommendations for improved trailer design and management approaches to reduce the variation in environmental conditions on the trailer included:
– The times when there is greatest potential for the pigs to experience thermal stress are when the trailer is stationary, either at the farm or at the plant, when air movement is low; these are times when greatest care is needed to prevent problems.
– As expected, there was considerable variation in environmental conditions on the trailer between seasons. However, there was also considerable variation within season in conditions between the decks and compartments of the trailer as well as for different times during the journey.
– Variation within the trailer in temperatures was greatest in the winter when, at the extreme, the difference between the compartments with the highest and lowest temperature was ~26oC (47oF).
– Temperatures were generally higher in the front compartments compared to other locations, which probably reflects the likely direction of air flow within the trailer (rear to front).
Suggested improvements in trailer design include:
– Varying the ventilation openings (size, shape and position) along the trailer side to produce the required ventilation rate to keep air velocity and other environmental conditions within comfortable ranges for the pig.
– Developing a system (ideally automated) for changing side wall openings based on external conditions to allow for more rapid changes in ventilation rates across all compartments in response to rapidly changing conditions that can occur during any journey.
– Installation of ventilation fans in the front end walls of the trailer to increase ventilation rates under hot conditions, particularly when the trailer is stationary.
– Establishing the heat transfer characteristics of various bedding materials to determine the most appropriate dry bedding material to use in cold weather and the most appropriate wetted bedding material to use in hot weather (to improve heat transfer via evaporation).
Further research is required to fully validate the model developed in this project. Also, future studies should focus on taking measurements at several locations within each compartment, use air velocity sensors that indicate the direction as well as the speed of air flow, and include data collected with different pig stocking densities on the trailer.
