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ANIMAL PRODUCTION |
Pork Industry Institute, Department of Animal and Food Sciences, Texas Tech University, Lubbock 79409
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Abstract |
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 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Key Words: animal welfare • cortisol • pig • space requirement • transport
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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). Stocking density is one important aspect of transport that could affect animal health and welfare, especially in pigs already experiencing weaning stress, which has been shown to affect the immune response, performance, and behavior in pigs (Hay et al., 2001; Kanitz et al., 2002).
Most studies evaluating effects of space requirements of pigs during transport have been conducted on market-weight pigs. Greater stocking densities have been associated with greater mortality rates (Warriss, 1998; Ritter et al., 2004). Stocking density during transport has also been shown to influence physiological measures of stress and fatigue in pigs including concentrations of lactate dehydrogenase and creatine phosphokinase (Barton-Gade and Christensen, 1998; Warriss et al., 1998; Kim et al., 2004). The behavior of an animal during transit is also an important factor to take into consideration when determining the appropriate space requirements during transport. Adequate space allowance during transit is important because pigs generally prefer to lie down after a period of standing if the conditions are suitable.
Transport stress has been shown to influence several physiological and behavioral measures in pigs. Furthermore, suboptimal space allowance during transport can reduce the welfare and health of pigs. The objective of this research was to establish a first estimate of the space requirements of weaned pigs during a 60-min transport in summer by using a multidisciplinary approach including physiology, immunology, and behavior.
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Animals, Housing, and Experimental Design
Pigs used in this study were a Landrace, Large White, and Duroc cross. All sows were fed a diet to meet or exceed NRC (1998) nutrient requirements. Pigs were not offered creep feed before weaning. Water was provided ad libitum in the farrowing crates.
A commercial semi-trailer was fitted with experimental compartments that provided 0.05, 0.06, and 0.07 m2/pig. All 3 experimental compartment sizes were represented on the upper and lower decks of the trailer. One hundred pigs were transported in each experimental compartment, so group size did not confound compartment size. This study was replicated 4 times. Only a subset of the 100 pigs were sampled for blood analysis. Over the entire study, 96 BW-matched (5.1 ± 0.10 kg) pigs (18 ± 1 d of age) from 16 sows/litters were allocated to 1 of 3 space allowances: 0.05, 0.06, and 0.07 m2/pig. Barrows and gilt were represented equally over all space allowances. In total, 32 pigs (16 gilts and 16 barrows) per treatment and compartment size were used (n = 96 total).
The initial component of this experiment was conducted at a gestation to weaning facility. Before weaning, blood samples were collected from all experimental pigs and pigs were ear tagged, weighed, lesion scored, and then returned to their home pen until weaning. Skin lesions were scored as 0 (no lesions), 1 (minor), or 2 (severe). Blood samples were collected by placing pigs in a supine position and collecting 5 mL of blood from the anterior vena cava using heparin-coated Vacutainers (87 USP units of heparin; BD, Franklin Lakes, NJ; procedure lasted approximately 1 min) for analysis of hematological, blood chemistry, and immune measures. Blood samples were placed on ice after collection until analysis was performed.
Approximately 30 min after blood collection, all pigs (experimental and nonexperimental pigs) were removed from the farrowing crates and moved into holding pens. Experimental pigs were placed with "filler" pigs, so that group size was held constant at 100 pigs per experimental compartment. Pigs were loaded onto the semi-trailer. Male and female pigs were segregated on different decks of the trailer, as is common practice on commercial swine facilities. The sex of pigs on each deck was alternated so as not to confound trailer deck level with sex effects. Once all pigs were loaded on the trailer, the trailer was transported to the wean-to-finish site. The truck followed the same route for each replication which took 60 ± 5 min. The trailer was equipped with Hobo data loggers (Onset Computer Corporation, Bourne, MA) to record temperature, humidity, and wind speed. A Hobo data logger was secured at pig height in each experimental pen within the trailer. Wind speed averaged 1.77 m/s during the entire trip. Temperature ranged from 26.1 to 30.3°C during transport with an average temperature of 28.4 ± 1.23°C. Relative humidity ranged from 50.0 to 60.0% during transport with an average relative humidity of 59.8 ± 4.42%.
At the wean-to-finish site, experimental pigs were located, weighed and lesion scored, and a blood sample was collected. Pigs were again held in a supine position and 10 mL of blood was collected from the anterior vena cava using heparin-coated Vacutainers (143 USP units of heparin; BD; procedure lasted approximately 1 min) for analysis of hematological, blood chemistry, cortisol, and immune measures.
Blood Analysis
Whole blood (before and after transport) was analyzed to determine white and red blood cell counts, differential leukocyte counts, hemoglobin, hematocrit, mean corpuscular volume, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentrations, and red blood cell distribution width using a cell counter (Cell-Dyn 1800, Abbott Laboratories, Abbott Park, IL), and the neutrophil to lymphocyte (N:L) ratio was calculated by dividing the percentage of granulocytes by the percentage of lymphocytes. Blood samples were centrifuged for 20 min at 660 x g at room temperature and plasma collected for analysis of cortisol concentrations and blood chemistry measures. Cortisol and blood chemistry were analyzed on only half of the samples (n = 16 pigs/treatment). Cortisol concentrations were analyzed using an enzyme immunoassay kit with a sensitivity of 0.6 ng/mL (Assay Designs, Ann Arbor, MI). Intra- and interassay CV were 6.3 and 6.7%, respectively. The use of this assay was published in Sutherland et al. (2008). Blood chemistry was analyzed using the Roche/Hitachi 912 auto-analyzer (Roche Diagnostics, Basel, Switzerland) for blood urea nitrogen (BUN), creatinine, glucose, total protein, albumin, aspartate aminotransferase (AST), creatine kinase (CK), alkaline phosphatase, gamma-glutamyl transferase, and total bilirubin.
Neutrophils were isolated from 10 mL of whole blood as described by Hulbert and McGlone (2006). The phagocytosis assay was performed to determine the number of latex beads engulfed by neutrophils, and the percentage of cells phagocytosing at least one bead was calculated as described previously (Hulbert and McGlone, 2006). The chemotaxis assay was performed according to published methods (Salak et al., 1993; Hulbert and McGlone, 2006). Briefly, migration of neutrophils across a polyvinylpyrrolidone-free filter (pore size of 5 µm; Neuro Probe, Molecular Probes, Eugene, OR) toward media or recombinant human complement C5a (chemotaxis) was measured.
Behavior
Digital still cameras were placed in each experimental compartment to record the behavior and postures of the pigs during transport (Table 1). Cameras were programmed to take 1 picture per minute (1-min scan samples). Behaviors and postures measured included lying, standing, sitting, standing/rearing on top of another pig, and lying/huddling on top of another pig. Behaviors are described in Table 1; all behaviors were mutually exclusive. The frequency of each behavior was calculated over the transport period and divided into four 15-min periods.
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A Wilson-brand straight deck stock trailer (Wilson Trailer Company, Sioux City, IA) was used during all replications of this study. The trailer was fitted with an upper and a lower deck. The trailer contained compartments that were adjusted to provide 0.05, 0.06, and 0.07 m2/pig based on pigs weighing approximately 5 kg and with each compartment holding 100 animals. Each of the 3 space allowances were represented on each of the upper and lower decks of the trailer. Wood shavings were spread over the upper and lower decks before the pigs were loaded.
Statistical Analysis
All data were tested for constant variance and departures from normal distribution. Data lacking normality were transformed logarithmically using log10 function. Data were subjected to ANOVA using the MIXED procedure (SAS Inst. Inc., Cary, NC). Data were analyzed as a random complete block with the trailer as the block. The experimental unit was the pen. The main fixed effects were block (4 levels), sex (2 levels), deck (2 levels), treatment (3 levels), and time (2 levels). Random effects in the model were litter (16 levels) and piglet (96 levels). The interaction between treatment and time (df = 4) and treatment and deck (df = 4) were included in the model. A total of 16 litters and 96 pigs (treatment, n = 32; gilts, n = 16 and barrows, n = 16) were used in this study. Gilts and barrows were balanced within each sampling period. Behavioral data were also analyzed using ANOVA using the MIXED procedure (SAS Institute Inc.). The behavior observation period was divided into four 15-min periods. For behavioral measures, the main fixed effects were block (4 levels), sex (2 levels), deck (2 levels), treatment (3 levels), and period (4 levels). The interaction between treatment and period (df = 5) and treatment and deck (df = 4) were included in the model.
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RESULTS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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). No sex, deck, or treatment x deck effects were observed for white blood cell measures (P > 0.05).
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). The N:L ratio was greater (P < 0.005) for pigs transported at 0.05 m2/pig compared with pigs transported at 0.06 and 0.07 m2/pig (Figure 1).
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). No other differences (P > 0.05) in hematological values were observed. No sex, deck, or treatment x deck effects were observed for hematological values (P > 0.05).
Plasma cortisol concentrations were greater (P < 0.001) than baseline after transport regardless of space allowance (Table 3). No sex, deck, or treatment x deck effects were observed for cortisol concentrations (P > 0.05).
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). Blood urea nitrogen, albumin, AST, CK, and gamma-glutamyl transferase were greater (P < 0.01) for pigs after transport regardless of space allowance (Table 3). No sex, deck, or treatment x deck effects were observed for blood chemistry values (P > 0.05). Chemotaxis in response to the mitogen human complement C5a did not differ (P > 0.05) among pigs transported at different space allowances (0.05 m2/pig: 9.2 ± 2.05 cells/5 fields; 0.06 m2/pig: 6.2 ± 2.20 cells/5 fields; 0.07 m2/pig: 5.0 ± 2.13 cells/5 fields). For all results, the least squares means and SE are presented. The percentage of neutrophils that engulfed at least one latex bead did not differ (P > 0.05) among pigs transported at different space allowances (0.05 m2/pig: 91.7 ± 2.54%; 0.06 m2/pig: 89.8 ± 2.76%; 0.07 m2/pig: 95.9 ± 2.65%). No sex, deck, or treatment x deck effects were observed for immune measures (P > 0.05).
Body weight decreased (P < 0.05) after transport, regardless of space allowance (before transport: 5.2 ± 0.08 kg; after transport: 5.0 ± 0.07 kg). Skin lesion scores increased (P < 0.001) after transport, regardless of space allowance (before transport: 0.08 ± 0.030; after transport: 0.67 ± 0.072). Furthermore, lesion scores were greater (P < 0.05) in barrows than gilts (barrows: 0.4 ± 0.05; gilts: 0.3 ± 0.05).
Pigs transported at 0.05 m2/pig spent less (P < 0.05) time lying than pigs transported at 0.06 or 0.07 m2/pig between 16 and 60 min after transport (Figure 2). Pigs transported at 0.05 m2/pig spent more (P < 0.05) time standing than pigs transported at 0.06 and 0.07 m2/pig during the last 15 min of transport (Figure 3).
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DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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). The N:L ratio was greater for pigs transported at 0.05 m2/pig compared with pigs transported at 0.06 or 0.07 m2/pig, suggesting that pigs transported at 0.05 m2/pig may have experienced more stress than pigs transported at 0.06 or 0.07 m2/pig. Transport caused a stress response in weaned pigs that may have been exacerbated for pigs transported at 0.05 m2/pig.
Space allowance influenced the behavior of weaned pigs during transport. Pigs transported at 0.05 m2/pig lay down less than pigs transported at 0.06 and 0.07 m2/pig between 30 and 60 min after transport, suggesting that pigs transported at 0.05 m2/pig were more restless than pigs transported at 0.06 or 0.07 m2/pig. Early-weaned pigs transported between 0 and 6 h at a space allowance of 0.06 m2/pig rested for 71% and stood for 26.5% of the time during transport in summer (Lewis and Berry, 2006). In the present study, weaned pigs transported for 60 min at a space allowance of 0.06 m2/pig spent 68% of the time standing and 19% of the time lying. The differences between these studies are probably due to differences in the length of transport. At the beginning of the transport period in the present study 88% of pigs were standing, whereas during the last 15 min of the trip only 49% of the pigs were standing, suggesting that given a longer transport duration pigs in this study would have spent more time lying down. Kim et al. (2004) found that standing behavior during transport was less in low (0.39 m2/100 kg) compared with medium (0.35 m2/100 kg) and high (0.31 m2/100 kg) stocking density rates in market-weight pigs. However, Barton-Gade and Christensen (1998) did not find that giving market-weight pigs more space resulted in more lying behavior; on the contrary, they observed continuous disturbances from other pigs, and, at stocking densities of 0.42 m2/100 kg and 0.5 m2/100 kg, pigs had more difficulty maintaining balance. In the present study, the behavior of weanling pigs during transport suggests that a space allowance of 0.06 or 0.07 m2/pig was preferable to 0.05 m2/pig when transporting weaned pigs.
Creatine kinase is released from muscle fibers into the circulation in response to exercise or tissue damage and is a good indicator of muscular activity or tissue damage (Van der Meulen et al., 1991; Fàbrega et al., 2002; Yu et al., 2007). Creatine kinase was greater in weaned pigs after transport, regardless of space allowance. Values of CK measured after transport were in the upper limit of the normal range for CK (Carr, 1998). Creatine kinase concentrations also increased in slaughter-weight pigs in response to transport stress (Elbers et al., 1991; Fàbrega et al., 2002). Furthermore, CK concentrations increased in market-weight pigs kept at stocking densities less than 0.5 m2/100 kg during transport (Barton-Gade and Christensen, 1998; Warriss, 1998); however, space allowance did not affect CK concentrations in weaned pigs in this study.
Aspartate aminotransferase, which is widely distributed in the myocardium, liver, and skeletal muscles, is a good indicator of muscular activity or tissue damage (Van der Meulen et al., 1991; Yu et al., 2007). Aspartate aminotransferase was increased in transported pigs regardless of space allowance, but was within the normal range for weaned pigs (Carr, 1998). Elevated CK and AST concentrations measured in transported weaned pigs were probably due to tissue damage caused by muscle exertion as a result of transport, but concentrations were still within the normal range for these enzymes, suggesting that the welfare of these pigs was not compromised.
Blood urea nitrogen is a metabolic waste product in the blood generated from the breakdown of protein. Concentrations of BUN in this study were in the upper limit or slightly above the normal range (Carr, 1998; Mersmann and Pond, 2001) in weaned pigs after transport. The increased BUN concentrations among transported pigs may indicate muscle and protein breakdown. Therefore, increased concentrations of BUN in addition to increased CK and AST in pigs after transport suggest that pigs may have been in a catabolic state because of exertion during transport.
Total plasma protein and plasma albumin concentrations are markers for protein homeostasis, which increase with dehydration. Albumin concentrations usually parallel total protein concentrations. Total protein and albumin were increased but within the normal range (Carr, 1998; Mersmann and Pond, 2001) for weanling-age pigs, suggesting that pigs may have been experiencing mild dehydration as a result of transport. In addition, hematocrit increased and BW was less after transport compared with baseline, further suggesting that these pigs were mildly dehydrated as a result of a 60-min transport.
Skin lesion scores were greater in barrows than in gilts overall. One possibility is that barrows may fight more than gilts. However, McGlone (1985) found that the frequency of aggressive behavior after mixing young pigs did not differ between young gilts and castrated males. Weaning and transporting pigs involve the mixing of unfamiliar pigs, which often results in fighting to establish new dominance orders (McGlone, 1985). Fighting in pigs can cause stress, possibly resulting in fatigue (Warriss, 1998). Lewis and Berry (2006) found that early-weaned pigs transported at 0.06 m2/pig showed infrequent fighting during transport, but more pigs were shown to fight when transported in summer compared with winter. Therefore, fighting of pigs during weaning and transport could add to the stress response experienced by pigs during transport and, furthermore, cause an increase in indices of muscle damage such as CK and AST concentrations.
The increased blood chemistry values and reduced BW in transported weaned pigs suggest that these pigs were experiencing dehydration and muscle breakdown due to transport; however, space allowance did not further affect these values. Different space allowances during transport did not influence any immune or physiological measures in this study; however, the greater N:L ratio and increased standing behavior in pigs transported at 0.05 m2/pig suggest that space allowances of 0.06 and 0.07 m2/pig are preferable when transporting pigs for 60 min in summer. This study was designed to determine a first estimate of space requirements of weaned pigs during transport. Further research is necessary before trucking quality assurance recommendations can be made regarding the space requirements of weaned pigs during transport in summer.
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Footnotes |
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2 Corresponding author: mhairi.sutherland{at}ttu.edu
Received for publication April 1, 2008. Accepted for publication August 19, 2008.
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LITERATURE CITED |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
), 0.06 m2/pig (
), and 0.07 m2/pig (
) during a 60 min transport period in summer. In each time period, least squares means ± SE accompanied by a * indicates that 0.05 m2/pig differed (P < 0.05) from 0.06 m2/pig; # indicates that 0.05 m2/pig differed (P < 0.05) from 0.07 m2/pig; and + indicates that 0.06 m2/pig differed (P < 0.05) from 0.07 m2/pig.