The pot-belly trailer, which can transport large loads in a single journey, is commonly used for swine transportation in Canada. However, it is generally acknowledged that pot-belly trailers and some specific compartments within this vehicle are worse than others in terms of animal losses. The objective of this study was to evaluate the effects of pot-belly design on animal welfare and meat quality in pigs being transported long distance in two different seasons of the year.

1. Introduction

In Western Canada, the large extension of the territory coupled with the centralization of the slaughter industry, with more pigs being killed in fewer larger plants, forces producers to transport pigs for long distances. This has resulted in the increased use of pot-belly (PB) trailers that can transport large loads (up to 230 pigs) in a single journey. However, due to the presence of multiple steep internal ramps, pigs are more difficult to handle while loading and unloading this vehicle type, resulting in higher risk of animal losses during transport compared to other vehicle types. In North America, a higher percentage of in-transit deaths and non-ambulatory pigs have been both recorded in summer (+0.15% and +2%, respectively) and in winter (+0.10% and +0.20%, respectively) compared to winter and summer, respectively. These increases have been associated with the use of the PB trailer compared to a double-decked truck or a flat-deck trailer that are equipped with hydraulic decks . Both cold and heat stress have an impact on ante- and post-mortem muscle glycogen stores leading to higher incidence of DFD (dark, firm, dry) and PSE (pale, soft, exudative) pork, respectively. Recently, a greater percentage of PSE loins was found in the summer compared to winter (3% vs. 1%) and a greater incidence of DFD loins was reported in winter than in summer (8% vs. 4%) under Eastern Canadian transport conditions. In two previous studies, the animal location (deck and/or compartment position in the truck) in the PB trailer during summer trasportation has an impact on pig body temperature and meat quality variation, with higher gastro-intestinal tract temperature in pigs in the upper deck and a greater percentage of pale pork being found in the upper and bottom decks compared to other locations. These effects are very likely the result of the physical exertion required by pigs to negotiate the ramps to get to these compartments under warm ambient conditions. However, these results were obtained in short distance transportation trials (2 h trip). Sutherland et al. and Weschenfelder et al. reported no detrimental effects on animal welfare when the PB trailer was used for a 9- and 7-h trip, respectively. However, in the former study no interaction between trailer type and season was found, while in the latter one these results were obtained under mild environmental conditions (11.2 °C on average). There is no evidence of the effects of the season and animal location on stress response and meat quality of pigs transported long distance in a PB trailer. Because there is a gap in the knowledge on the role of ambient temperature and long-distance transportation on the variation of physiological variables and pork quality of pigs transported with a PB trailer, the objective of this study was to examine the physiological response (heart rate and exsanguination blood stress indicators) as well as skin bruise score and meat quality of pigs transported 8 h to slaughter in different transport compartments during both summer and winter.

2. Experimental Section

2.1. General

All experimental procedures performed in this study were approved by the AAFC Animal Care Committee in Sherbrooke (QC) based on the current guidelines of the Canadian Council on Animal Care. A total of 2,145 crossbred pigs (BW = 115.2 ± 6.8 kg) were transported for 8 h (565 km) in summer (June and July, 2008; average temperature of 18.4°C, ranging from 9.1 to 20.7 °C) and winter (January to March, 2008; average temperature of –10.4°C, ranging from -22.3 to -9.7 °C) seasons from the Prairie Swine Center Elstow Research growing-finishing unit in Saskatchewan to a slaughter plant located in Brandon (Manitoba) using a dual-purpose (cattle and pig) pot-belly (PB) trailer.
Pigs were transported in 5 weeks in winter and 6 weeks in summer, in terms of one load of 195 pigs per week in each season, at an average density of 0.42 and 0.41 m2/pig, respectively. During the experiment, the transport schedules changed between the seasons to concur with the current transport practices of the region. In summer, the transporter only had two short stops (15 and 30 min each) after an initial transport phase of 190 min. These stops were considered short enough to protect pigs from the temperature and humidity rise inside a stationary PB trailer. In winter, the transporter only had a single stop, lasting 180 min, before continuing the journey to the abattoir. Pigs were transported on three decks and distributed into 9 out of 10 compartments (four on the upper deck, three in the middle deck and two in the bottom deck of the vehicle; Figure 1). Compartment 6 was not filled due to load limitations. The trailer included three internal ramps: a 22° ramp going to the upper level (compartments 1, 2, 3 and 4), a 32° ramp going to compartment 5 (“bottom-nose” or BN), and a 22° ramp giving access to the bottom level (compartments 9 and 10; Figure 1). The trailer was bedded with wood shavings in the summer and straw and wood shavings in the winter. The side panels were open 100% in the summer, but only 10% in the winter. The trailer compartments were loaded in the following order: 5, 1, 2, 4, 3, 9, 10, 7, and 8. At loading, pigs were moved along an alley, up the chute into the trailer and then through ramps in groups of four or five using boards and the electric prod as necessary. The loading crew did not change between seasons.

Figure 1. The location of compartments and distribution of pigs by compartment in the pot-belly trailer. Internal ramps are solid lines in compartments 5, 8, and 10.

Pot-belly trailer

The location of compartments and distribution of pigs by compartment in the pot-belly trailer

Within a group of six pigs in each compartment, one pig (30 pigs/trip or replicate: total of 330 pigs) was chosen for physiological evaluation (heart rate and blood analysis). This pig plus another one selected out of every four pigs (45 pigs/replicate: total of 495 pigs) within the same group were also used for the meat quality assessment. Only barrows were chosen for these evaluations. Feed was withdrawn from the pigs 5–6 h prior to transport. Pigs were transported for 8 h and unloaded at the plant using boards and electric prods as necessary. After 1.5 to 2 h in lairage, pigs were driven in a single line to stunning, were electrically stunned (head-to-chest electrical stunning) and exsanguinated in the prone position.

2.2. Physiological Measurements

Heart rates were recorded by Polar heart rate monitors (Polar Electro Canada) at 5 s intervals for the duration of loading and transportation. For protection and stable positioning, heart rate monitors were covered by leather or nylon weight-lifting belts buckled around the pig’s chest. These were installed 24 h prior to transportation to allow animals to recover from the stress of this handling procedure. Belts were removed immediately after unloading. Data were downloaded and the average heart rate for each pig was determined for each of the experimental periods up to and including unloading. At exsanguination, 2 mL of blood were collected in a tube (BD Vacutainers®, VWR International Ltd., Montreal, Canada) containing 6 mg of NA2 EDTA and 3 mg of NaF solution to extract plasma for lactate analysis and 10 mL of blood were put in a tube (BD Vacutainers®, VWR International Ltd., Montreal, Canada) to extract serum for creatine-kinase (CK) analysis. The 2-mL blood tubes were immediately centrifuged at 4 °C for 10 min at 1,400 × g. Plasma was then transferred into 1.5 mL Eppendorf tubes and stored at -80 °C until lactate determination. Serum samples were kept at room temperature (~23 °C) for 1 h before refrigeration at 4 °C. The following day, serum samples were centrifuged at 4 °C for 10 min at 1,400 × g, transferred to 1.5 mL Eppendorf tubes, and stored at -80 °C until analysis. Plasma lactate concentrations were measured with a microplate reader using a commercially available kit (Lactate Assay Kit, Biomedical Research Service Center, University of Buffalo, Buffalo, NY, USA) whereas CK concentrations were measured with a spectrophotometer using a creatine kinase-sl kit (Creatine Kinase-SL Assay of Chemicals Diagnostic Limited, Vancouver, Canada). All analyses were done in triplicate. The intra-assay coefficients of variation for CK and lactate concentration data were 3.43 and 3.40%, respectively.

2.3. Measurement of Carcass Quality Traits

Following slaughter, carcasses were eviscerated, split and blast chilled for 2 h. Hot carcass weight (HCW) and lean meat yield were recorded to characterize the population under study.
Skin damage was assessed on the day of slaughter in the cooler using the 5-point, photographic scale (1 = none to 5 = severe), whereas bruises were classified as fighting-type bruises (score 1 = less than 5 bruises; 2 = 6 to 10 bruises; and 3 = greater than 10 bruises) and mounting-type bruises (score 1 = less than 5 bruises; 2 = 6 to 10 bruises) by visual assessment of shape and size according to the photographic standards of the Institut Technique du Porc. According to the ITP scale, bruises due to biting during fighting are recognized as being of 5–10 cm in length, comma shaped and concentrated in high number in the anterior (head and shoulders) and posterior (ham) regions of the carcass. Long (10 to 15 cm), thin (0.5 to 1 cm wide) comma shaped bruises densely concentrated on the back of pigs typically caused by the fore claws were classified as mounting-type bruises. Lacerations and scratches normally produced when pigs are handled aggressively and run in closed and tight spaces were also noted and classified as “other bruise types”.

2.4. Meat Quality Measurements

Measurements of pH were made at 6 h post-mortem (after blast chilling) in the longissimus thoracis (LT) muscle at the third/fourth last rib level and Semimembranosus (SM) muscle and at 24 h (pHu) post-mortem in the LT, SM and Adductor (AD) muscles using a temperature-compensating, spear-type probe (Cole-Palmer Instrument Co., Vernon Hills, IL, USA) attached to a pH meter (pH 100 series; Oakton Instruments, Vernon Hills, IL, USA). At 24 h post-mortem, color data were collected on the LT and SM muscle after a 45 min bloom period. Visual color was evaluated using the Japanese color standards [15] in the LT muscle only, whereas instrumental color (L*, a*, and b* values) was measured with a Minolta Chromameter (CR-300; Minolta Canada Inc., Mississauga, Canada) equipped with a 25 mm aperture, 0° viewing angle, and D65 illuminant in the LT and SM muscles. Drip loss was measured in the LT muscle using the modified EZ-driploss method of Correa et al. Briefly, three 25 mm diameter cores were removed from the center of 2.5 cm thick LT (removed at the third/fourth last rib level) chop, weighed, and placed into plastic drip loss containers (Christensen Aps Industrivaengetand, Hilleroed, Denmark), before being stored for 48 h at 4 °C. At the end of the 48 h storage period, muscle cores where removed from their containers, surface moisture was carefully dabbed, cores were reweighed, and drip loss percentage was calculated by dividing the difference between initial and final core weights by the initial core weight.

2.5. Statistical Analysis

The experimental design was a one-way factorial (with the compartments as the levels of the factor to be compared) in a randomized complete block design (weeks as blocks) using the SAS software (SAS 2002) and repeated mixed model analyses (for heart rate data only) to test for any effects of season, compartment, transport event and their interactions. Considering the difference in transport schedule between seasons, for a reliable comparison only heart rate data recorded in the initial transport phase, which was of the same length in each season, were considered in the analysis. Carcass and meat quality data were analyzed by analysis of variance of SAS (SAS Institute Inc., Cary, NC, USA). A probability level of P < 0.05 was chosen as the limit for statistical significance in all tests.