J. Anim Sci. 2008. 86:3137-3145. doi:10.2527/jas.2008-0873
© 2008 American Society of Animal Science
Effects of season and distance moved during loading on transport losses of market-weight pigs in two commercially available types of trailer1
M. J. Ritter*,2,
M. Ellis*,3,
R. Bowman
,
J. Brinkmann,
S. E. Curtis*,
J. M. DeDecker*,4,
O. Mendoza*,
C. M. Murphy*,
D. G. Orellana*,
B. A. Peterson*,
A. Rojo*,
J. M. Schlipf* and
B. F. Wolter
* Department of Animal Sciences, University of Illinois, Urbana 61801; and
The Maschhoffs Inc., Carlyle, IL 62231
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Abstract
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This study evaluated effects of trailer design and season on physical indicators of stress during loading and unloading and transport losses (dead and nonambulatory pigs) in market-weight pigs (BW = 129.6 ± 0.40 kg). A total of 109 trailer loads of pigs (n = 17,256 pigs) from 1 farm were used in a randomized complete block design with a 2 x 4 factorial arrangement of treatments: 1) trailer design (potbelly vs. straight-deck) and 2) season (spring vs. summer vs. fall vs. winter). A subset of loads (n = 42) was used to examine effect of distance pigs were moved during loading [short (<24 m) vs. long (47 to 67 m)] on physical indicators of stress and transport losses. This study was conducted on 7 d per season at 1 farm with 4 loads (2 on potbelly and 2 on straight-deck trailers) being transported each day to 1 commercial packing plant. Pigs from different farm groups were mixed on the trailer and provided with 0.45 m2/pig floor space during an approximately 4-h journey to the plant. The percentage of pigs exhibiting open-mouth breathing, skin discoloration, and muscle tremors was recorded during loading and unloading. Additionally, dead pigs on arrival at the plant and nonambulatory pigs at the farm and at the plant were recorded. Effects of trailer design on open-mouth breathing and skin discoloration during unloading were dependent on season (trailer design x season interaction; P < 0.05). Pigs unloaded from potbelly trailers had a greater (P 
0.05) incidence of open-mouth breathing in the spring and summer and a greater (P < 0.05) incidence of skin discoloration in the spring, summer, and winter than pigs unloaded from straight-deck trailers. The incidence of total nonambulatory pigs at the plant was greater (P < 0.05) in the winter than in the spring and summer. The long compared with short distance moved treatment resulted in a greater (P = 0.001) incidence of open-mouth breathing and skin discoloration during loading and tended (P = 0.06) to increase the incidence of nonambulatory pigs at the farm. However, there was no effect of trailer design, season, or loading distance on total losses at the plant. In summary, physical indicators of stress (open-mouth breathing and skin discoloration) were increased with the long distance moved during loading treatment and were greater during unloading for potbelly than straight-deck trailers; however, trailer design, season, and loading distance had minimal effects on total transport losses.
Key Words: distance moved • nonambulatory • pig • season • trailer design • transport loss
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INTRODUCTION
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Losses of market-weight pigs (dead and nonambulatory animals) during transport to the packing plant is an emerging issue in the US swine industry with major implications for animal well-being and economics (Ellis et al., 2003
). The incidence of nonambulatory oninjured pigs has been associated with stress levels experienced by the animal (Ivers et al., 2002), and several factors can influence the level of stress experienced by the pig during transport including trailer design, season, and distance moved during loading.
Trailer design has potential implications for ease of pig movement and environmental conditions inside the trailer and transport losses (dalla Costa et al., 2007). Two trailer designs that are widely used to transport pigs in the United States are potbelly and straight-deck. A major difference between these is the greater number of internal ramps in potbelly than in straight-deck trailers that could result in more stress on the pigs during loading and unloading (Warriss et al., 1991). No controlled studies have been carried out on effects of these 2 designs on transport losses.
There is limited published information on seasonal effects on transport losses under US conditions; it has been reported that transport losses are greatest in the late fall and early winter months (Ellis and Ritter, 2006). It is important to establish seasonal variation in transport losses as well as causes of this variation.
Modern swine finishing buildings in the United States are commonly 
100 m in length, resulting in pigs being moved relatively long distances during the loading process. Ritter et al. (2007) reported that loading distance can affect rate of nonambulatory pigs at the farm and at the plant; additional research is necessary to confirm these findings.
The objectives of this study were to compare 2 commercially available trailer designs and study effects of season and distance pigs are moved during loading on physical indicators of stress and transport losses.
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MATERIALS AND METHODS
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The protocol for this study was approved by the University of Illinois Institutional Animal Care and Use Committee.
Production Site
All pigs used in this study were from 1 site within a large production system. The site consisted of 10 finishing buildings, which are described in Table 1. Buildings 1, 2, 3, and 4 were connected via a center aisle-way and shared a common permanent loading ramp located in building 2. Buildings 5, 6, 7, 8, 9, and 10 each had 2 identical rooms; a portable loading ramp was used to load pigs from the end of each of these buildings. Pigs were moved into the buildings at an average BW of approximately 25 kg into mixed-sex pens of 25 to 40 pigs. Pigs were of a standard commercial genotype and were raised and managed according to standard procedures used by the production system. Animals had ad libitum access to corn-soybean meal-based diets and to water during the rearing period; feed and water were not withheld before pigs were loaded onto trucks for this study.
Experimental Design
This study was carried out as a randomized complete block design with a 2 x 4 factorial arrangement of the following treatments: 1) trailer design (potbelly vs. straight-deck) and 2) season (spring vs. summer vs. fall vs. winter) to evaluate the impact of these factors on physical indicators of stress, transport losses, and carcass trim loss. A total of 109 trailer loads of slaughter-weight pigs (BW = 129.6 ± 0.40 kg) consisting of 17,256 animals were used. A subset of these trailer loads of pigs (n = 42) were utilized in a split-split plot design with a 2 x 2 factorial arrangement of the following treatments: 1) trailer design (potbelly vs. straight-deck) and 2) distance moved during loading [short (<24 m) vs. long (47 to 67 m)] to evaluate the impact of these factors on physical indicators of stress and transport losses. The distance moved during loading treatments was compared within 6 trailer compartments on both trailer types. Therefore, trailer design was the main plot, trailer compartment was the subplot, loading distance was the sub-subplot, and date of transport was the blocking factor.
The number of loads for each trailer type by season and the buildings that the pigs came from are summarized in Table 2. The 42 loads used for evaluation of distance moved during loading were taken from buildings 5, 6, 7, 8, 9, and 10 on days when it was possible to have a minimum of 2 loads (1 for each trailer type) from a single barn.
Trailer Design Treatments
Two standard designs (pot-belly vs. straight-deck) of commercial livestock trailers were evaluated (Wilson Livestock Trailers, Sioux City, IA). Pigs were loaded and transported on 1 d per wk for 7 wk during each season, with 4 loads of pigs (2 on pot-belly trailers and 2 on straight-deck trailers) being transported on each day. Both the pot-belly and straight-deck trailers had 2 decks and were constructed of aluminum with punched holes in all of the trailer sides for ventilation. The basic design and construction of the 2 trailer types were relatively similar with the exception that the dimensions of the compartments, the height of the decks, and the internal loading ramps (5 internal ramps in the pot belly design vs. 1 internal ramp in the straight-deck design) differed (Tables 3 and 4; Figures 1 and 2).
Season
This study was carried out in all 4 seasons with pigs being transported on 7 d in each season. On each transport day, 2 pot-belly and 2 straight-deck trailers were loaded in random order and transported to the packing plant. Spring loads were transported in April and May 2005; summer loads were transported in August and September 2005; fall loads were transported in September, October, and November 2005; and winter loads were transported in January and February 2006. The ambient conditions for the 4 seasons, measured at a weather station close to the farm for the days that the pigs were transported, are presented in Table 5.
Distance Moved During Loading Treatments
The effect of distance moved during loading (short vs. long) was evaluated on a subset of 42 trailer loads of pigs that were transported by pot-belly (21 loads) or straight-deck (21 loads) trailers in each of the 4 seasons from buildings 5, 6, 7, 8, 9, and 10 (Table 1
). Pigs on the short loading distance treatment were from the first 7 pens in the buildings (between 4 to 24 m from the loading ramp), and those on the long loading distance treatment were from the last 7 pens in the buildings (between 47 to 67 m from the loading ramp). Pigs were given a unique mark with livestock marking spray before loading that corresponded to loading distance treatments to allow for treatment identification at the plant.
Loading distance treatments were compared within 6 similar-size compartments located in the same general area on both decks of each trailer design (Tables 3 and 4). Approximately equal numbers of pigs from the short and long distance treatments were mixed in each of the 6 test compartments on each trailer. This was accomplished by using 2 loading crews to simultaneously load pigs moved short and long loading distances. Loading crews alternated between the short and the long distance moved treatments to prevent the potential confounding of loading distance treatment with loading crew. The remaining nontest compartments were filled with pigs from the middle 6 pens of the buildings that were located between 27 and 44 m from the loading ramp.
Pig Handling and Transportation Procedures
All loading procedures were carried out by University of Illinois personnel to standardize the handling procedures across loads and trailer designs. Loading took place between 0100 and 0700 h with unloading of pigs at the plant taking place between 0600 and 1200 h on each day. The standardized handling procedure consisted of moving groups of 4 to 6 pigs from the pen onto the trailer using sorting boards and, if necessary, electric goads, which were used sparingly and only when pigs refused to move. The widths of the center aisle and the loading ramp, and the angles of the loading ramp for each building are presented in Table 1. For both trailer types, pigs from different farm pens were mixed in each compartment and were provided with approximately 0.45 m2/pig floor space on the trailer during transport. The incidence of pigs that became nonambulatory at the farm during loading was recorded; however, only those that became nonambulatory after they had been loaded onto the trailer were transported to the plant. Pigs were transported a distance of approximately 290 km to a commercial packing plant, a journey that took approximately 4 h. The journey was from the same farm to the same plant for all loads of pigs and involved travel on rural roads and interstate highways. University of Illinois personnel unloaded all 4 trailer loads of pigs on each day, using a livestock paddle, sorting board, and when necessary, an electric goad. During winter months, wood shavings were spread on the floor of each deck to a depth of approximately 2.5 cm, and a proportion of the side trailer vents were covered (at the discretion of the driver) to reduce air movement through the truck and associated chilling. Temperature and relative humidity sensors (HOBO data loggers, Bourne, MA) continuously monitored conditions inside the trailer from the start of loading at the farm to the end of unloading at the plant. Pot-belly trailers were equipped with 7 temperature and humidity sensors, whereas straight-deck trailers were equipped with 8 sensors (Figures 1 and 2). The total pig weight on the trailer and the percentage of carcasses that required trimming were obtained at the packing plant for each load of pigs.
Assessment of Physical Indicators of Stress
The number of pigs exhibiting open-mouth breathing, skin discoloration, and muscle tremors were recorded during loading at the farm and during unloading at the plant for all of the pigs transported in the 6 test compartments on pot-belly and straight-deck trailers.
Classification of Transport Losses
Transport losses were recorded in the plant up to the time at which the pigs crossed the weigh scale. All dead and nonambulatory pigs were identified by plant employees. Nonambulatory pigs were defined as pigs that could not walk or were having difficulty walking and could not keep up with the remainder of the group (Anderson et al., 2002; Ellis et al., 2003). University of Illinois personnel classified nonambulatory animals as injured or fatigued. Fatigued pigs were defined as nonambulatory, noninjured pigs that displayed classic symptoms of stress-related problems (open-mouthed breathing, skin discoloration, muscle tremors, or a combination of these). Injured pigs were animals exhibiting visible signs of an injury.
Statistical Analysis
Before analysis, all outliers, defined as observations falling outside the range of the mean ± 3 SD, were identified and removed and all data were tested for normality by using PROC UNIVARIATE (Version 9.1; SAS Inst. Inc., Cary, NC). Data for transport losses, physical indicators of stress, and carcass trim loss were not normally distributed and were transformed before analysis with a 
2 rank-based transformation using PROC RANK of SAS.
Effects of trailer design and season on physical indicators of stress, transport losses, and carcass trim loss were analyzed as a randomized complete block design using PROC MIXED of SAS. Transport date was the blocking factor, and the trailer load of pigs was the experimental unit. The model used included fixed effects of trailer design, season, and the trailer design x season interaction, and the random effect of transport date nested within season.
Effects of distance moved during loading on physical indicators of stress and transport losses at the plant were analyzed as a split-split plot design using PROC MIXED of SAS. The main plot was trailer design, the subplot was trailer compartment, the sub-sub plot was loading distance, and the blocking factor was transport date. The model used included fixed effects of trailer design, loading distance, and the trailer design x loading distance interaction and random effects of loading date, trailer compartment nested within trailer design, the loading date x trailer design interaction, and the loading date x trailer design x trailer compartment interaction. The experimental unit and error term used to test main effects of loading distance were the loading distance group within trailer compartment and the residual error, respectively.
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RESULTS AND DISCUSSION
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Transport Conditions and Losses
Details of transport times and conditions for loads transported in the pot-belly and straight-deck trailers are summarized in Table 6. Total number of loads (53 and 56 for the pot-belly and straight-deck trailer, respectively), number of loads per day (1.89 and 2.00, respectively), number of pigs per load (157 and 160, respectively), and average BW per load (130.2 and 129.0 kg, respectively) were similar across the 2 trailer designs. Event times were generally similar for both trailer designs with the exception that time to unload was considerably greater (P < 0.001) for the pot-belly compared with the straight-deck trailers (36 vs. 20 min, respectively). This difference largely reflects the greater difficulty experienced by handlers in getting the pigs to move easily from pot-belly trailers.
Number of pigs per load, transport floor space, and times for the various events within transportation process were typical of the production system within which this research was carried out and of the industry in general. The average BW of pigs transported (approximately 130 kg) was somewhat heavier than current industry averages (122.3 kg; USDA-NASS, 2007), and the time taken to load pigs onto the trailer was greater than normal because of requirements of experimental protocol.
Effects of trailer design and season on temperature and relative humidity inside the trailer are presented in Table 6. In general, temperatures within the trailer were greater for straight-deck than pot-belly trailers at all stages of the transportation process, with the difference in average temperature being 1.6°C (Table 6). Relative humidity levels in the trailer at the farm were similar for the 2 designs (Table 6); however, during transport, waiting at the plant, and unloading, relative humidity inside the trailer was approximately 5 percentage units less on the straight-deck compared with the pot-belly design. Observed differences between the 2 trailer designs for temperature and relative humidity inside the trailer were unexpected and are difficult to explain. It is unclear if these observed differences result from trailer design features or are due to chance, and this area merits additional research.
Effects of Trailer Design and Season
Effects of trailer design and season on physical indicators of stress and transport losses are summarized in Tables 7 and 8, respectively. There was no effect (P > 0.05) of trailer design on the incidence of any of the indicators of stress during loading at the farm (Table 7). This is not surprising given that a significant component of the stress associated with loading is experienced by the animal before it reaches the transport trailer. The incidence of pigs exhibiting muscle tremors after loading and unloading was low and was not affected (P > 0.05) by season or trailer design (Table 7). However, there were trailer design x season interactions (P < 0.05) for the incidence of open-mouth breathing and skin discoloration after unloading (Table 7). Pigs unloaded from pot-belly trailers had greater (P < 0.05) rates of open-mouth breathing in spring and summer, and had greater (P < 0.05) rates of skin discoloration in spring, summer, and winter than pigs unloaded from straight-deck trailers. Also, electric goad use during unloading (data not shown) was greater for pot-belly than straight-deck trailers with pigs in 7.3% of compartments on pot-belly trailers requiring some use of electric goads compared with none of the compartments on the straight-deck trailers. This reflects the greater difficulty experienced in moving pigs off the pot-belly trailers, which was also illustrated by the greater time taken to unload these trailers compared with the straight-deck trailers (Table 6). Collectively, these results suggest that pigs transported on pot-belly compared with straight-deck trailers may experience greater stress during unloading, the extent of which could depend on environmental conditions.
Given the effects of trailer design on physical indicators of stress during unloading, it is interesting to note that there was no effect of trailer design on either transport losses or carcass trim loss (Table 8). A recent commercial survey conducted by Sutherland et al. (2006) reported that pot-belly trailers had greater (P < 0.01) rates of dead on arrival at the plant than straight-deck trailers (0.18 vs. 0.15%, respectively), but in that survey there was no effect of trailer design on total transport losses (dead and nonambulatory pigs). However, caution should be taken when interpreting these survey results as the effects of trailer design are potentially confounded with several important factors, including farm of origin, truck driver, transport floor space, and transport times and conditions that could also influence transport loss. Additionally, the current study only evaluated 1 manufacturer’s design of potbelly trailers that had 2 decks, whereas the survey of Sutherland et al. (2006) most likely included data on transport losses from pot-belly trailers with a wider variety of design features (e.g., 2 or 3 decks).
The percentage of nonambulatory pigs at the plant was greater (P < 0.05) in winter than in spring and summer, but there was no effect of season on the incidence of nonambulatory pigs at the farm or on the incidence of other transport losses at the plant (Table 8). Several studies have reported that transport losses are greater in summer months (Allen et al., 1974; Smith and Allen, 1976; Warriss and Brown, 1994). However, the increased incidence of nonambulatory pigs observed in the winter months agrees with other field studies conducted in the Midwestern US (Ellis and Ritter, 2006) and elsewhere (Gosalvez et al., 2006). Additional research is necessary to understand the reasons for seasonal influences on transport losses.
Distance Moved During Loading
There were no interactions (P > 0.05) between trailer design and distance pigs were moved during loading for physical indicators of stress or transport losses, and therefore, only main effects of distance moved during loading are reported in Table 9. The long distance treatment (47 to 67 m) resulted in greater (P < 0.001) incidences of open-mouth breathing and skin discoloration during loading and tended (P = 0.06) to increase the incidence of nonambulatory animals at the farm during loading than the short distance moved treatment (4 to 24 m; Table 9). Incidence of skin discoloration during unloading was greater (P = 0.01) for pigs moved the short compared with the long distance; however, the overall incidence of pigs with skin discoloration was low and the difference between the distance moved treatments was small (Table 9). Thus, moving pigs the long compared with the short distance during loading had no negative effects on physical indicators of stress during unloading or transport losses at the plant (Table 9), and these results are similar to those of Ritter et al. (2007). In a previous study (Ritter et al., 2006), we observed that the majority (72%) of pigs that were classified as nonambulatory at the farm after being loaded onto the trailer had recovered during a 3-h journey and were normal and ambulatory at the plant. The journey time in the current study was approximately 4 h, and it is possible that pigs were able to rest and recover from the stress associated with loading during the journey to the plant. However, pigs moved long distances during loading may not be able to recover from loading stress during shorter journeys (for example of 1 h or less), and thus, understanding effects of loading distance on transport losses for pigs transported short distances warrants additional research.
In summary, moving pigs long distances (47 to 67 m) during loading and transporting pigs in pot-belly trailers increased the incidence of pigs displaying physical indicators of stress (open-mouth breathing and skin discoloration during loading and unloading, respectively) compared with short loading distances (<24 m) and using straight-deck trailers. Additionally, the percentage of nonambulatory pigs at the plant was greater in the winter than in the spring and summer. However, trailer design, season, and the distance pigs were moved during loading had minimal effects on total transport losses at the plant. Additional research is necessary to evaluate effects of loading distance on transport losses after shorter journey times (<1 h) and to understand why the incidence of nonambulatory pigs increases during the winter months in the Midwest of the United States.
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Footnotes
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1 The authors acknowledge the assistance of various staff at the University of Illinois, The Maschhoffs Inc., Cloonen Trucking, Maschhoff Transport LLC, and Cargill Meat Solutions for their assistance in collecting trial data. Additionally, we acknowledge the financial support of the National Pork Board (Des Moines, IA). 
2 Current address: Elanco Animal Health, 56776 241st Street, Suite 200, Ames, IA 50010.
4 Current address: Michigan State University, 181 Agriculture Hall, East Lansing, MI 48824.
3 Corresponding author: mellis7{at}uiuc.edu
Received for publication January 16, 2008.
Accepted for publication May 9, 2008.
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LITERATURE CITED
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dalla Costa, O. A., L. Faucitano, A. Coldebella, J. V Ludke, J. V. Peloso, D. dalla Rosa, and M. J. R. Paranhos da Costa. 2007. Effects of season of the year, truck type and location on truck on skin bruises and meat quality in pigs. Livest. Sci. 107:29–36.[CrossRef]
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Ellis, M., and M. Ritter. 2006. Impact of season on production: Transport losses. Pages 205–207 in Proc. 2006 Allen D. Leman Swine Conf., St. Paul, MN.
Gosalvez, L. F., X. Averos, J. J. Valdelvira, and A. Herranz. 2006. Influence of season, distance and mixed loads on the physical and carcass integrity of pigs transported to slaughter. Meat Sci. 73:553–558.[CrossRef]
Ivers, D. J., L. F. Richardson, D. J. Jones, L. E. Watkins, K. D. Miller, J. R. Wagner, R. Seneriz, A. G. Zimmermann, K. A. Bowers, and D. B. Anderson. 2002. Physiological comparison of downer and non-downer pigs following transportation and unloading at a packing plant. J. Anim. Sci. 80(Suppl. 2):39. (Abstr.)
Ritter, M. J., M. Ellis, C. R. Bertelsen, R. Bowman, J. Brinkmann, J. M. DeDecker, K. K. Keffaber, C. M. Murphy, B. A. Peterson, J. M. Schlipf, and B. F. Wolter. 2007. Effects of distance moved during loading and floor space on the trailer during transport on losses of market-weight pigs on arrival at the packing plant. J. Anim. Sci. 85:3454–3461.[Abstract/Free Full Text]
Ritter, M. J., M. Ellis, J. Brinkmann, J. M. DeDecker, M. E. Kocher, K. K. Keffaber, B. A. Peterson, J. M. Schlipf, and B. F. Wolter. 2006. Effect of floor space during transport of market-weight pigs on incidence of transport losses at the packing plant and relationships between transport conditions and losses. J. Anim. Sci. 84:2856–2864.[Abstract/Free Full Text]
Smith, L. P., and W. M. Allen. 1976. A study of the weather conditions related to the death of pigs during and after their transportation in England. Agric. Meteorol. 16:115–124.[CrossRef]
Sutherland, M. A., A. McDonald, and J. J. McGlone. 2006. Factors influencing the percentage of dead and fatigued pigs during transport. Page 609 in Proc. 19th IPVS Congr., Copenhagen, Denmark.
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Abstract
INTRODUCTION
