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ANIMAL PRODUCTION |
* Department of Animal Sciences, University of Illinois, Urbana 61801;
and
The Maschhoffs Inc., Carlyle, IL 62231; and
Elanco Animal Health, Greenfield, IN 46140
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Abstract |
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 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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Key Words: distance moved • floor space • nonambulatory • pig • transport loss
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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). However, limited data are available regarding either causes of transport losses or appropriate management strategies to reduce these transport losses under commercial conditions.
A major cause of nonambulatory pigs is suspected to be metabolic acidosis resulting from the stress of handling and transportation (Anderson et al., 2002; Ivers et al., 2002). Two factors that may influence the stress level experienced by pigs during handling and transportation and, consequently, the incidence of non-ambulatory pigs, are the distance that pigs are moved from their home pen to the trailer and the floor space per pig on the trailer. We previously reported that increasing transport floor space from 0.39 to 0.48 m2/pig reduced transport losses by 59% (Ritter et al., 2006). However, increasing transport floor space per pig has implications for transportation costs. The floor space that results in minimal transport losses has not been established under US conditions.
Modern finishing facilities can exceed 100 m in length, and the loading ramp is commonly positioned at one end of the building. Consequently, some animals are required to move relatively long distances during loading. Exercise in pigs increases body temperature, heart rate, respiration rate, and blood lactate while decreasing blood pH (Kallweit, 1982; Zhang et al., 1989). Thus, moving pigs long distances during loading could predispose them to developing metabolic acidosis and becoming nonambulatory. The objectives of this study were to determine effects of distance moved before loading onto the trailer at the farm on transport losses and to identify the transport floor space at which dead and nonambulatory pigs were minimized under commercial conditions.
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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Experimental Design and Treatments
Effects of distance moved during loading and transport floor space on the incidence of transport losses were evaluated in a study involving 42 trailer loads of pigs. The study used a split-plot design with a 2 x 6 factorial arrangement of the following treatments: 1) loading distance [short (0 to 30.5 m from the exit of the building) or long (61.0 to 91.4 m from the exit of the building)] and 2) transport floor space (0.396, 0.415, 0.437, 0.462, 0.489, or 0.520 m2/pig). Loading distance treatments (subplots) were compared within floor space treatments (main plot). Transport floor space treatments were randomly assigned to 1 of 6 compartments on each trailer load, and both loading distances were compared within each compartment.
Animals and Farm
Market weight (BW = 131.2, SD 5.05 kg) barrows and gilts that were the progeny of PIC 337 sires and C22 dams (PIC US, Franklin, KY) were used in this study, which was conducted in 2 replicates that represented 2 consecutive barn batches from the same commercial site. There were 2 identical wean-to-finish buildings on the site that were 91.44 m in length. The buildings were operated as all-in-all-out with each batch (from filling the barn with newly weaned pigs to removing pigs from the barn to be transported for slaughter) taking approximately 6 mo. This study was carried out on 2 consecutive batches of pigs that were transported in October and the following April to May, respectively. Data were collected on 18 loads of pigs transported on 5 d of the first-barn batch (in October) and on 24 loads of pigs from 7 d of the second-barn batch (in April to May). Between the October batch and April to May batch, the buildings were renovated to widen the center aisle from 0.56 to 0.81 m and to double the width of the pens from 3.05 to 6.10 m (Table 1). Consequently, pigs were raised in mixed-sex pens of 28 and 56 pigs for the October batch and April to May batch, respectively. Before transportation, pigs had ad libitum access to feed until the time they were removed from the pen for loading.
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Straight-deck trailers constructed of aluminum with punched sides were used in this study (Wilson Livestock Trailers, Sioux City, IA). These trailers were owned and operated by the commercial site and had 5 compartments on the top deck, 6 compartments on the bottom deck, and an internal loading ramp (21° slope) for the top deck. The total floor space in each of the compartments ranged from 4.29 to 9.25 m2 (Table 2).
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). These floor spaces represented the range in transport floor spaces observed under US commercial conditions. The difference between each of the floor space treatments corresponded to a difference of 1 pig per compartment (Table 2). If these floor spaces were used for the entire trailer load, they would correspond to a total number of pigs transported of 188, 179, 169, 161, 152, and 144 pigs per load for 0.396, 0.415, 0.437, 0.462, 0.489, and 0.520 m2/pig, respectively. For each trailer load, the 6 floor space treatments were randomly assigned to 1 of the 6 test compartments; differences in floor space were created by varying the number of pigs in each compartment. Therefore, effects of transport floor space were evaluated on 4,662 pigs transported in 252 trailer compartments on 42 trailer loads of pigs. The nontest compartments on each trailer load were given a floor space of 0.45 m2/pig, which was the standard used by this production system. Loading Distance Treatments and Pig Handling
The effects of 2 loading distances [short (0 to 30.5 m from the exit of the building) or long (61.0 to 91.4 m from the exit of the building)] were evaluated. The loading distance treatments represented the range experienced by pigs loaded from barns of the size used in this study, which are typical of many commercial facilities. Each test compartment was filled with an approximately equal number of pigs that were moved either the short or long distances during loading. The number of pigs placed in a trailer compartment from each loading distance treatment ranged from 7 to 12.
Two loading crews, consisting of University of Illinois investigators and farm employees, loaded pigs alternately from the short and long treatments. For both treatments, 2 handlers removed the pigs from the pen using sorting boards only. Pigs were then moved by 1 handler in groups of 3 to 6 pigs through the center aisle of the building (0.56-m wide for the October replicate and 0.81-m wide for the April-May replicate), up a covered loading ramp (incline of 10°), and onto the trailer using sorting boards and, if necessary, electric goads. Pigs from a minimum of 4 pens in the barn (2 pens in the front of the barn and 2 pens in the back of the barn) were mixed in each compartment. Loading crews changed locations in the barn between loads to prevent confounding of loading distance with handling crew. Nontest compartments were filled with pigs housed in the middle of the barn (pens located 30.5 to 61.0 m from the exit). During loading, test pigs were given a unique colored mark with a livestock crayon, corresponding to the loading distance and floor space treatment subclass.
Transport Conditions
Pigs were transported approximately 3 h (240 km) to a commercial packing plant. Temperature and relative humidity sensors (HOBO H8 Loggers, Onset Computer Corporation, Bourne, MA) were placed on the gates of the first and third compartments on each deck of each trailer to continuously log (1-min intervals) environmental conditions within the trailer. Event times (loading, waiting period at the farm before transport, transport, waiting period at the plant before unloading, unloading, and total time from the beginning of loading to the end of unloading) were recorded, and the average temperature and relative humidity inside the trailer were calculated by event for each of the 4 locations in the trailer.
Assessment of Physical Signs of Stress and Identification of Dead and Nonambulatory Pigs
At both the farm during loading and the plant during unloading, University of Illinois personnel identified and recorded pigs that were displaying physical signs of stress (open-mouth breathing, skin discoloration, and muscle tremors). Additionally, the number of pigs that became nonambulatory at the farm during loading was recorded. However, only pigs that became nonambulatory at the farm after they were loaded on the trailer were transported.
Drivers unloaded the trailers using a sorting board and a livestock paddle. The number of pigs that died in transit was recorded by the transport floor space and loading distance treatments. Packing plant employees identified nonambulatory pigs on the truck, in the holding pen, and up to the point of the weigh scale. Nonambulatory pigs were defined as pigs that were unable to walk or keep up with the rest of the group (Anderson et al., 2002; Ellis et al., 2003). University of Illinois personnel classified nonambulatory pigs as either fatigued (uninjured and showing physical signs of stress), injured, or injured and fatigued (nonambulatory, injured pig displaying physical signs of stress). Total losses at the plant were the sum of dead and nonambulatory pigs.
Statistical Analysis
Data for transport losses and physical indicators of stress were not normally distributed and, thus were subjected to a 
2 rank-based transformation using the RANK procedure (SAS Institute Inc., Cary, NC). Transformed data were analyzed as a split-plot design using the MIXED procedure of SAS; the main plot was transport floor space, the subplot was loading distance, and the block was the trailer load of pigs. The model included fixed effects of replicate (barn batch date), transport floor space, loading distance, and all possible interactions and the random effects of transport day nested within replicate, trailer load nested within transport day and replicate, and the trailer load x transport floor space interaction. The experimental units for transport floor space and loading distance treatments were the trailer compartment and the loading distance treatment group within trailer compartment, respectively. Error terms used to test the main effects of transport floor space and loading distance were the load x transport floor space interaction and the residual error, respectively. Differences between least squares means were separated using the PDIFF option of SAS.
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RESULTS AND DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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Descriptive statistics for transport times and conditions are presented in Table 3. Loading times ranged from 43 to 90 min, which is longer than those observed in other studies (van Putten and Elshof, 1978; Ritter et al., 2006). This reflects the extra time needed to organize the loading of trailers according to the research protocol. Times for waiting at the farm, transport, waiting at the plant, and unloading averaged 6, 190, 11, and 21 min, respectively. The total time from the beginning of loading to the end of unloading averaged 288 min and ranged from 254 to 329 min.
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). Temperatures were, on average, lower during the waiting period at the plant at the end of the journey than at the farm, whereas relative humidity levels were generally greater at the plant than at the farm, although differences were small. Live Weights and Transport Losses
The average BW of the 6,953 pigs transported (4,662 in test compartments and 2,291 pigs in nontest compartments) was 131.2 kg with a range between loads from 118.5 to 139.8 kg (Table 4). On average, 0.20% of the pigs were classified as nonambulatory at the farm during loading. In addition, total losses during transport averaged 1.5% of pigs transported with a range between loads from 0.0 to 4.9% (Table 4). Pigs dead on arrival averaged 0.52% (range 0 to 3.0%), and nonambulatory pigs at the plant averaged 0.95% (range 0.0 to 3.6%). The number of injured pigs was relatively low (average 0.09%; range 0.0 to 1.2%), with the majority of nonambulatory animals being classified as fatigued (average 0.79%; range 0.0 to 3.61%). In addition, a small number of pigs (0.07%) were classified as being both injured and fatigued. These values were generally greater than those found in previous studies carried out under commercial conditions within the same production system used for this study (Ellis et al., 2003; Ritter et al., 2006).
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There was no effect (P 
0.28) of replicate (barn batch date) on the incidence of transport losses (Table 5). Similarly, the distance pigs were moved from the pen to the truck had no effect (P 0.06) on transport losses. However, there was a trend for nonambulatory pigs at the farm (0.08 vs. 0.32 ± 0.09%; P = 0.09) and for the incidence of injured pigs at the plant (0.04 vs. 0.24 ± 0.07; P = 0.06) to be greater for pigs moved the longer loading distances.
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. Pigs transported in April to May showed a greater (P < 0.05) incidence of open-mouth breathing during loading and more skin discoloration during unloading than those transported in October. Also, pigs moved the long distance during loading showed a considerably greater incidence of open-mouth breathing during loading than those moved the short distance (P < 0.001). However, there was no effect (P > 0.05) of loading distance on the incidence of skin discoloration during loading and unloading or on the incidence of muscle tremors during loading (Table 6).
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). In contrast, there was no effect of loading distance on the incidence of muscle tremors during unloading for the October replicate, whereas the incidence was greater for pigs moved the greater distance for the April to May replicate. However, treatment differences for the incidences of both open-mouth breathing and muscle tremors during unloading were small and of limited practical significance.
Fatigued pigs are in a state of metabolic acidosis (Anderson et al., 2002; Ivers et al., 2002). Kallweit (1982) and Zhang et al. (1989) established that treadmill exercise increases body temperature, heart rate, respiration rate, and blood lactate concentrations while reducing blood pH in pigs. Based on these findings, it was anticipated that pigs moved the long loading distances would be more susceptible to developing metabolic acidosis and becoming nonambulatory than pigs moved the short distance. In the current study, loading distance did not affect percentage of dead or fatigued pigs at the packing plant, but pigs moved long loading distances exhibited more physical signs of stress during loading, as evidenced by a 2-fold increase in open-mouth breathing during loading, and had a much greater incidence (4-fold) of nonambulatory pigs at the farm (Tables 5 and 6). However, we have previously observed that most pigs displaying open-mouth breathing, skin discoloration, or both, at the farm during loading will fully recover during a 3-h journey to the plant (Ritter et al., 2006). Additionally, rectal temperature and blood acid-base values return to baseline resting values within 2 h after handling (Bertol et al., 2002; Hamilton et al., 2004). Therefore, it is possible that the 3-h journey to the plant in the current study provided enough time for pigs on the long distance treatment to fully recover, resulting in no effect of loading distance on total transport losses at the plant.
Effect of Floor Space During Transport
It should be noted that the approach used in this study to create the floor space treatments, which involved varying the number of animals per compartment with no adjustment of compartment size, resulted in the effect of floor space being confounded with the effect of number of pigs per compartment. However, this is the approach that would be used by producers under commercial conditions to adjust the floor space per pig on the trailer.
Floor space on the trailer had no effect on any of the physical indicators of stress assessed during loading at the farm, and there was no effect of floor space on the incidence of open-mouth breathing or muscle tremors during unloading at the plant (Table 7). The incidence of skin discoloration was less for pigs at 0.520 compared with those at 0.396, 0.415, and 0.462 m2/pig; however, the differences between the treatments were relatively modest.
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). In addition, floor space had no effect on the number of either injured animals or pigs that were both injured and fatigued at the plant. However, floor space did influence (P < 0.05) the incidence of pigs dead on arrival, total nonambulatory pigs, fatigued pigs, and total losses at the plant. Total transport losses were generally greater (P 
0.05) for the 3 least transport floor spaces (0.396, 0.415, and 0.437 m2/pig) than for the 2 greatest transport floor spaces (0.489 and 0.520 m2/pig). Additionally, pigs transported at 0.462 m2/pig had fewer (P < 0.05) total losses than pigs transported at 0.396 m2/pig (Table 8). Previously, we reported that increasing transport floor space from 0.39 to 0.48 m2/pig reduced the incidence of total nonambulatory pigs, fatigued (nonambulatory, uninjured) pigs, and total losses by 59% (Ritter et al., 2006). Therefore, the current study agrees with our previous findings and confirms that transport floor space can have a major effect on transport losses.
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). From these results, it would appear that the total transport losses for the pigs of the weights used in this study (
130 kg) were minimized at a floor space of 0.462 m2/pig or greater, although further study is required to more precisely define the floor space that minimizes losses. To put these results into context, current recommendations for transport floor space are 0.40 to 0.45 m2/pig for pigs weighing 114 to 136 kg (National Institute for Animal Agriculture, 2004). Additionally, pigs used in this study were transported for 3 h in the spring and fall when the weather was relatively mild.
One factor that can influence incidence of dead and nonambulatory and uninjured pigs during transport is the mutation of the halothane gene that is associated with increased stress susceptibility. There are no recently published estimates of the frequency of this mutation in contemporary US commercial pig populations. However, a recent survey of slaughter plants in the Midwest of the United States (Ellis et al., 2007) found that the frequency of animals that had at least 1 copy of the mutation was very low (<3%) in pigs that were either dead or nonambulatory and uninjured pigs on arrival at the plant, suggesting that this mutation is not a major factor in transport losses in the United States.
In summary, pigs moved long compared with short loading distances displayed more physical signs of stress during loading; however, loading distance did not affect transport losses. Furthermore, this study confirms that transport floor space has a major effect on transport losses. Additional research is necessary to establish the floor space on the trailer that minimizes transport losses for all conditions experienced in the United States (for different transport times and seasons).
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Footnotes |
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2 Current address: Elanco Animal Health, 56776 241st Street, Suite 200, Ames, IA 50010.
3 Corresponding author: mellis7{at}uiuc.edu
Received for publication April 23, 2007. Accepted for publication July 31, 2007.
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LITERATURE CITED |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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