HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Sutherland, M. A. Articles by Salak-Johnson, J. L. Search for Related Content PubMed PubMed Citation Articles by Sutherland, M. A. Articles by Salak-Johnson, J. L.

Impacts of chronic stress and social status on various physiological and performance measures in pigs of different breeds¹

Department of Animal Sciences, University of Illinois, Urbana 61801

	Abstract

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
Pigs typically experience various environmental stressors, which can negatively affect performance. Cortisol concentrations and various immune and performance measures are influenced by breed, but few data exist describing the impact of breed on stress responsiveness in pigs. The objective of this experiment was to determine if certain physiological responses to chronic stressors differed among 3 breeds and 2 commercial lines of pigs. The pigs were Landrace (n = 36), Meishan (n = 30), Yorkshire (n = 32), or 1 of 2 commercial lines (Line-A and Line-B; both n = 36). All pigs were weaned at 17 to 21 d and kept in a common nursery. At 49 d of age, pigs were assigned to 1 of 2 treatments: stress (heat, crowding, and mixing) or control (no stress treatment). Pigs were allocated to groups of 3 pigs per pen of the same sex. Control pigs were kept with their littermates. At the onset of the experiment, stressed pigs were mixed with 2 unfamiliar pigs once, and heat and crowding stressors were implemented simultaneously for 14 d. Pigs allocated to the stress treatment were video-recorded for 24 h following initiation of mixing to determine social status: dominant, intermediate, or submissive. Blood samples were taken at d 0 (baseline), 1, 7, and 14 to assess cortisol concentrations and immune measures. Breed and treatment affected cortisol, immune, and performance measures, but no significant breed x treatment interactions were found. In general, pigs subjected to the chronic stressor had lower (P < 0.001) BW and ADG (P < 0.001) than did control pigs. Plasma cortisol was lower (P < 0.001) among stressed pigs at d 7 and 14. Regardless of breed, lipopolysaccharide-induced proliferation (P < 0.01) and natural killer (NK; P < 0.005) cytotoxicity were greater in stressed pigs compared with controls. Furthermore, among stressed pigs, dominant pigs had a greater total white blood cell count (P < 0.005), NK (P < 0.05), and phagocytosis (P < 0.05) than the subordinate pigs. The results indicate that pig breed did not influence the physiological responses to the chronic concurrent stressors imposed for 14 d in this study, but social status did influence the immune responsiveness of these pigs to heat, crowding, and mixing.

Key Words: breed • immune • performance • pig • social status • stress

	INTRODUCTION

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
Pigs are confronted by many stressors during production (Hyun et al., 1998). Stress has immunosuppressive effects that potentially decrease immune function, thereby increasing disease susceptibility (Hermann et al., 1993). The time that it takes for pigs to reach market weight can be prolonged by exposure to environmental stress (Hyun et al., 1998). More specifically, high ambient temperature (Nienaber et al., 1991; Xin and DeShazer, 1992), social mixing (McGlone and Curtis, 1985; Björk et al., 1988), and restricted floor space (Kornegay et al., 1993a,b) reduce feed intake and BW gain.

Breed effects on immune and endocrine measures in response to various stressors such as restraint (Rosochacki et al., 2000), a novel environment (Desautes et al., 1999), and a bacterial challenge (Nguyen et al., 1998) have been reported in pigs. Pig social status can influence immune responses following acute stressors including heat, shipping, and mixing stresses (McGlone et al., 1993; Hicks et al., 1998; Tuchscherer et al., 1998). For example, acute shipping and cold stress reduced natural killer (NK) cytotoxicity more in subordinate pigs than in dominant pigs (McGlone et al., 1993; Hicks et al., 1998).

Few studies have reported differences between breeds in immune responses to various stressors. Furthermore, data that assesses innate immune measures in response to 14 d of continuous multiple concurrent stressors imposed on pigs of different breeds are limited. We hypothesized that breed and social status would affect the innate immune system, performance, and cortisol measures in pigs in response to a 14-d chronic stressor. The objectives of this study were to determine: 1) effects of acute mixing and chronic crowding and heat exposure for 14 d on certain immune and performance measures in 3 breeds and 2 commercial lines of pigs, and 2) effects of social status on those physiological responses to the chronic simultaneous stressor complex.

	MATERIALS AND METHODS

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
Animal and Housing

Pigs used in this study were obtained either from the University of Illinois swine research farm or from a commercial farm. The breeds were Landrace (n = 36), Meishan (n = 30), Yorkshire (n = 32), or pigs from 2 commercial parent female genotypes, lines A and B (n = 36 per line). Piglets were weaned at 17 to 21 d of age and moved to a common nursery. Before the start of the experiment, pigs were allowed to adjust to their new environment for approximately 21 d.

Sets of 6 littermates (3 gilts, 3 barrows) were kept together in nursery pens (2.0 x 2.0 m; floor-space 0.33 m²/pig) equipped with a self-feeder and one nipple waterer. Light followed a 12 h light:12 h dark (on at 0600 h) cycle. Pigs had ad libitum access to water and a diet formulated to meet or exceed recommended nutrient allowances (NRC, 1998). The University of Illinois Institutional Animal Care and Use Committee approved all of the experimental procedures.

Experimental Design

Before allocation to treatment, a baseline (d 0) blood sample (20 mL) was taken by anterior vena cava puncture at 49 d of age. On d 0, control (no stress treatment) pigs were kept with their littermates but grouped at the rate of 3 pigs per pen (1.0 x 1.0 m; 0.33 m²/pig), so each pen contained littermates of the same sex.

For control pigs, air temperature was 22 ± 5°C, and relative humidity was approximately 50%. Pigs assigned to the multiple stressor treatment were initially mixed with 2 unfamiliar pigs of the same sex and placed in nursery pens with reduced floor-space allowance (0.5 x 0.5 m; 0.17 m²/pig). The floor-space allowance as recommended by the Pork Industry Handbook (Fritschen and Muehling, 1986) is 0.278 to 0.372 m² for pigs 13.6 to 27.2 kg; therefore, the floor-space allowance of 0.17 m² per pig is approximately one-half of the recommended floor-space allowance for pigs of this size.

Stressed pigs were kept at 33 ± 5°C (relative humidity was approximately 50%). Temperatures decreased slightly at night with fluctuating outdoor temperatures. Stressors were imposed for 14 consecutive days. Pens of gilts or barrows were randomly distributed throughout the nursery to avoid block effects on sex. Pigs of each breed were equally represented between control and stress treatments, and sex was evenly represented across breeds and treatments.

All pigs were injected s.c. at the base of the ear with 1 mL of 40% sheep red blood cell (SRBC; Sigma, St. Louis, MO) on d 0 and 7 of the study. Behavior was recorded for the first 24 h after initiation of the stressors to determine social status among the stressed pigs. Pig BW was measured before and at the end of the study.

Blood Sample Collection

Pigs were held in a supine position, and 20 mL of blood was collected into vacutainers containing heparin (143 USP), by anterior vena cava puncture (blood sampling lasted approximately 1 min) at d 0 (baseline), 1, 7, and 14. Ten milliliters of whole blood was centrifuged at 660 x g for 20 min, and plasma was removed for cortisol, immunoglobulin G (IgG), and SRBC hemagglutination analysis after storage at –20°C. The remaining 10 mL of whole blood was used for total white blood cell (WBC) numbers, differential percentages, and cell isolation. Plasma cortisol and immune measures were not affected by bleeding order (data not shown).

White Blood Cell and Differential Counts

Whole blood was evaluated to determine total WBC numbers and leukocyte differential counts. Total WBC were counted using an electronic Coulter Z1 Particle Counter (Beckman Coulter, Miami, FL) at 1:1,000 dilution, and red blood cells were lysed before counting. Whole blood smears were fixed in methanol and stained with Hema-3 staining system (Fisher Scientific, Houston, TX) to determine differential percentages of lymphocytes, neutrophils, monocytes, and eosinophils. Slides were viewed under a light microscope, and 100 cells per slide were visually counted.

Cortisol

Plasma samples were assayed for cortisol using a Coat-A-Count cortisol kit, following the manufacturer’s protocol (Diagnostic Products, Los Angeles, CA). Briefly, in duplicate, 25 µL sample or standard was added to antibody-coated tubes. Radiolabeled (I¹²⁵) cortisol was added to tubes and incubated 45 min at 37°C in a water bath. The liquid phase was decanted and radioactivity counted using a gamma counter (Cobra II, Perkin-Elmer, Boston, MA). A standard curve based on 0, 10, 50, 100, 200, and 500 µg/mL was used. A high (200 µg/mL) and low (10 µg/mL) control were used to determine intra- and interassay CV. Intra- and in-terassay CV were 4.6 and 19.0%, respectively. The minimal detectable cortisol concentration using this assay was approximately 2 ng/mL.

Immunoglobulin G

An enzyme-linked immunosorbent assay was used to measure total porcine IgG, as described by Morrow-Tesch et al. (1994), with minor modifications. Briefly, plasma samples were diluted 1:3,000 in 0.05% Tween-PBS. In duplicate, 120 µL of diluted sample or standard was added to a 96-well microtiter plate coated with porcine IgG (Jackson Immunoresearch, West Grove, PA). Rabbit anti-pig IgG (120 µL; 5.7 µg/mL; Sigma) was added to each well, and the plates were incubated for 2 h at room temperature and then washed. Enzyme-linked anti-rabbit IgG (200 µL; Jackson Immunore-search) was added to each well, and the plates were incubated for 1 h at room temperature and then washed. Substrate solution (200 µL; 1 mg/mL of P-nitrophenyl phosphate; Sigma) was added to each well, and the plates were incubated for 30 min. The reaction was stopped with 100 µL of 2M NaOH, and the plates were read using a microplate reader (BIO-TEK Instruments, Winooski, VT) at a wavelength of 405 nm (intra-and interassay CV were 6.1 and 16.5%, respectively).

Sheep Red Blood Cell Hemagglutination

The hemagglutination assay was performed in duplicate to determine antibody response of the pig to SRBC, according to methods of Blecha and Kelley (1981). Briefly, plasma samples were thawed and heat-inactivated for 30 min in a 57°C water bath. Heat-inactivated samples (200 µL) were added to a 96-well round-bottom plate; PBS (100 µL; Diamedix, Miami, FL) was added, and samples were serially diluted. To each well, 100 µL of 1% SRBC was added, and the plates were covered and then incubated for 24 h at room temperature. The SRBC titers were determined by sedimented cells forming a distinct pattern on the bottom of the wells. The greatest dilution yielding a positive reaction was deemed the titer.

Cell Isolation

Porcine lymphocytes and neutrophils were isolated from 10 mL of whole blood by density gradient centrifugation using Histopaque-1077 (density = 1.077 g/mL; Sigma) and Histopaque-1119 (density = 1.119 g/mL; Sigma). Whole blood was diluted with Roswell Park Memorial Institute (RPMI) media and layered over Histopaque-1077 and -1119 (Sigma), then centrifuged at 700 x g for 30 min at room temperature. Lymphocytes were collected from the 1077 layer, washed twice in RPMI, resuspended, and counted. Neutrophils and RBC were removed from the 1119 layer and washed once in RPMI. Red blood cells were lysed using cold endotoxin-free water, and isotonicity was restored using 10 x PBS. Neutrophils were centrifuged for 10 min at 475 x g, and the supernatant was decanted, and the pellet was washed twice and resuspended in RPMI.

Natural Killer Cytotoxicity

Natural killer cytotoxicity was measured using a commercially available nonradioactive cytotoxicity detection kit, following the manufacturer’s protocol (Roche Diagnostics, Indianapolis, IN) and a radioactive NK assay protocol originally described by Lumpkin and McGlone (1992), with modifications. Briefly, porcine lymphocytes were used as effector cells, and K-562 chronic human myelogenous leukemia cells (American Tissue Type Culture Collection, Manassas, VA) were used as target cells. Lymphocytes were adjusted to 1 x 10⁷ cells/mL, and K562 cells were adjusted to a constant 10,000 cells per well. Samples were run in triplicate at effector:target ratios of 12.5:1, 25:1, 50:1, and 100:1, respectively. Percentage cytotoxicity was calculated as described by Lumpkin and McGlone (1992).

Lymphocyte Proliferation

A mitogen-induced lymphocyte proliferation assay (LPA) was performed to measure metabolic activity of lymphocytes, as described by Morrow-Tesch et al. (1994), with minor modifications. Briefly, lymphocytes were adjusted to 5 x 10⁶ cells/mL and placed in triplicate into a sterile 96-well flat-bottom plate. The mitogens concanavalin A (ConA; Sigma) and lipopolysaccharide (LPS; E. coli O55:B5; Sigma), respectively, were added at 0, 25, and 50 µg/mL. Plates were incubated for 72 h at 37°C under 5% CO₂ in a humidified incubator. Twenty microliters of MTT [3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide; Sigma] was added to each well, and the plates were incubated for 4 h. Acidified isopropanol (100 µL, 0.1 N HCl in anhydrous isopropanol) was added, and the plates were incubated overnight at 37°C and then read using a microplate reader (BIO-TEK Instruments) at a wavelength 550 nm with a reference wavelength 690 nm. The results were expressed as a proliferation index (PI):

Neutrophil Chemotaxis and Phagocytosis

The ability of neutrophils to migrate toward assay medium (control; random migration), recombinant human complement-5a (hC5a; Sigma), or porcine interleukin-8 (pIL-8; Sigma) [chemotaxis (CHTX); directed migration] was measured using an assay described by Salak et al. (1993). Briefly, in duplicate, medium, hC5a (10^–7 M), and pIL-8 (100 µg/mL) were added to the bottom wells of a 48-well microchemotaxis chamber (Neuro Probe, Gaithersburg, MD), and neutrophils adjusted to 3 x 10⁶ cells/mL in RPMI were added to the top wells of the chamber and incubated for 45 min. The polyvinylpyrrolidone-free filter (pore size 5 µm; Neuro Probe) was fixed and stained using the Hema-3 system (Fisher Scientific). Four fields per well were counted in blind fashion using a light microscope at 100x magnification.

Neutrophil phagocytosis (PHAGO) was measured using a flow cytometry-based assay as described by Jolie et al. (1997), with minor modifications. Briefly, neutrophils were adjusted to a cell concentration of 2 x 10⁶ cells/mL, and fluorescent beads (yellow-green, 1.0 µm; Molecular Probes, Eugene, OR) were added to each sample at a 10:1 ratio, incubated for 40 min at 37°C on a rotator, then centrifuged for 5 min at 1,000 x g. The samples were washed once in 1 mL of RPMI, decanted, resuspended in 1 mL of RPMI, and fixed in 4% para-formaldehyde. The samples were protected from light and held at 4°C until analyzed. Percent fluorescence was measured using an XL flow cytometer (Beckman Coulter). Data were transformed logarithmically, and the results were expressed as the total percentage of neutrophils engulfing one or more beads.

Haptoglobin

Haptoglobin concentrations were determined by a single radial immunodiffusion kit, following the manufacturer’s protocol (Porcine Haptoglobin Measurement Kit, Cardiotech Services, Louisville, KY). The intraassay CV of duplicate estimates was 2.4%.

Behavioral Data Collection

To establish social status, pigs allocated to acute mixing and 14 d of heat and crowding were video-recorded in time lapse for the first 24 h after the initiation of mixing. Video records were viewed in real time. The winner or loser of each agonistic encounter was recorded using previously described methodology (McGlone, 1985). Briefly, social status was assigned based on the outcomes of all agonistic encounters, and pigs were identified as dominant (DOM), intermediate (INT), or subordinate (SUB). Essentially, DOM pigs won every agonistic encounter in which they were engaged, whereas INT pigs lost one or more fights to a DOM pig. A pig was identified as SUB based on submissive postures repeatedly displayed to the other pigs within the group.

Statistical Analysis

All measures were tested for departures from normality using the UNIVARIATE procedure of SAS (SAS Inst., Inc., Cary, NC). Data lacking normality were transformed logarithmically using log₁₀ (neutrophil numbers, percentage of monocytes and eosinophils, cortisol, IgG, SRBC titers, Haptoglobin, CHTX, LPA, and NK). Minimum values for percentages of monocytes and eosinophils, CHTX, and SRBC titers, respectively, were zero; thus a value smaller than the lowest nonzero number was added to all observed values to allow for logarithmic transformations.

A linear mixed-effects model was used to analyze these variables using the Mixed procedure of SAS. The main fixed effects included were breed (5 levels), sex (2 levels), day (3 levels), and treatment (2 levels) or social status (3 levels). Social status and treatment were not run consecutively because social status and treatment were confounded; social status was only known for the stress-treatment pigs. Data from d 0 were used as a covariate to compensate for baseline variation. All second-order interactions were evaluated and nonsignificant (P > 0.05) interactions removed from the model. Random effects of litter and pen were included in the model. The model had a repeated structure for day, which allowed the incorporation of heterogeneity of variances across days. Residuals were tested for departures from assumptions.

	RESULTS

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
Physiological Response to Stress

Effects of multiple concurrent stressors on physiological and performance measures over time are presented in Table 1. Pig performance, measured by BW (P < 0.001) and ADG (P < 0.001), was lower in stressed pigs than in controls.

Plasma cortisol differed over time between treatment groups (treatment x day, P < 0.01). At d 1, there were no differences (P = 0.10) between stressed and control pigs, but at d 7 and 14 plasma cortisol was lower (P < 0.001) in stressed pigs. Moreover, there was no treatment difference for plasma IgG (P = 0.19), SRBC (P = 0.53), or haptoglobin (P = 0.19) at any time (P 0.30).

At effector:target ratio of 50:1, NK cytotoxicity was greater (P < 0.005) in stressed pigs than in controls at d 1 and 14. Also, LPS-induced B-cell LPA was greater (P < 0.01) in stressed pigs than in controls at d 1 and 14, but there was no treatment effect (P = 0.75) on ConA-induced T-cell LPA at any time (P 0.81).

Neither neutrophil CHTX in response to chemoattractants hC5a and pIL-8 nor PHAGO differed between treatments (P 0.23) at any time (P 0.41).

Social Status

Effects of pig social status on physiological and performance measures are presented in Table 2. In stressed pigs, social status influenced total WBC count; SUB pigs had lower (P < 0.005) total WBC than either INT or DOM pigs. Numbers of neutrophils (P = 0.34) and lymphocytes (P = 0.53) were not affected by social status. However, NK cytotoxicity was affected by social status; SUB pigs had lower (P < 0.05) NK cytotoxicity than did those determined to be DOM. Neutrophil PHAGO was greater (P < 0.05) in DOM pigs than in SUB pigs. Pig social status did not influence plasma cortisol (P = 0.45) or any performance measures (P 0.31).

Effects of breed on physiological and performance measures are presented in Table 3. Pig BW and ADG differed among breeds (P < 0.001). Body weight was greatest (P < 0.001) in Landrace pigs and lowest (P < 0.001) in Meishan. Overall, ADG was lowest (P < 0.001) in Meishan and Landrace pigs.

Plasma cortisol concentrations differed among breeds. Baseline cortisol was greater (P < 0.001) in Meishan and lower (P < 0.001) in Landrace pigs than in other breeds. Breed differences also occurred in IgG concentrations (P < 0.001); IgG concentrations were lower (P < 0.001) in Meishans than in any other breed. Haptoglobin concentrations also differed among breeds (P < 0.001); baseline values were lowest (P < 0.001) in Landrace and Yorkshire pigs.

There were breed differences for NK cytotoxicity (P < 0.001), such that baseline NK (50:1) was greater (P < 0.001) in Meishan pigs. Landrace pigs had lower (P < 0.001) NK cytotoxicity than did Meishan, Line-A, or Line-B pigs. The LPS- and ConA-stimulated LPA was influenced by breed (P < 0.005), and LPS and ConA-stimulated LPA was lowest (P < 0.05) in Yorkshire pigs.

Breed differences occurred in neutrophil CHTX in response to both hC5a and pIL-8 (P < 0.05). Directed CHTX was greatest (P < 0.001) in Line-B pigs. Neutrophil PHAGO was greatest (P < 0.001) in Line-A pigs and lowest (P < 0.001) in Landrace.

There was no treatment x breed interaction for physiological (P 0.12; except percentage of monocytes) or performance (P 0.09) measures. Furthermore, there was no sex difference for performance (P 0.45) measures or any physiological (P 0.11) measures except SRBC titer, which was greater (P < 0.05) in females (1.5 ± 0.09 vs. 1.2 ± 0.09).

	DISCUSSION

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
This study was designed to test the hypothesis that breed and social status influence the physiological responses to multiple stressors concurrently imposed for 14 d. These data support the hypothesis that 14 d of concurrent heat, crowding, and social tension affect certain aspects of the innate immune system, cortisol concentrations, and performance measures. However, breed of pig did not differentially affect the various responses to this chronic stressor. Moreover, social status affected certain aspects of the pigs’ immune response.

Environmental stressors are potential factors that contribute to the lag in BW gain that can lead to an increase in the number of days to market (Hyun et al., 1998). Pig BW and ADG were reduced in pigs subjected to acute mixing and chronic crowding and heat, implying that these stressors when imposed continuously for at least 14 d could increase the time it would take for pigs to reach market weight. High environmental temperature (Nienaber et al., 1991; Xin and DeShazer, 1992), social mixing (McGlone and Curtis, 1985; Björk et al., 1988), and restricted floor-space allowance (Kornegay et al., 1993a,b) can all reduce ADFI and BW gain in pigs. In fact, Hyun et al. (1998) found that the effects of individual stressors (heat, crowding, and social stress) are additive, implying for the current study that the combination of heat and crowding over the 14-d study period contributed to the reduction in BW and ADG observed in stressed pigs. Furthermore, BW and ADG were lowest in Meishan pigs and greatest in Landrace and Yorkshire pigs regardless of treatment allocation. This finding agrees with results reported by Sutherland et al. (2005) in which nonstressed Meishan pigs had lower BW and ADG and Yorkshire pigs had the greatest. Despite these robust breed differences in BW and ADG, there were no corresponding breed effects in response to the chronic 14-d stressor imposed in this study on these measures. This suggests that, regardless of breed, 14 d of heat, restricted floor space, and social tension due to social mixing leads to decreased BW and ADG.

Plasma cortisol was measured as an indicator of hypothalamic-pituitary-adrenal (HPA) axis activation in response to 14 d of heat stress, restricted floor space, and social tension due to mixing of pigs at d 0. Despite the consistently differential cortisol responses among breeds previously reported (Weiler et al., 1998; Desautes et al., 1999; Sutherland et al., 2005) and found in this study, pig breed did not affect the cortisol response to the chronic 14-d concurrent stressor imposed in this study. However, plasma cortisol was suppressed at d 7 and 14 in stressed pigs compared with non-stressed pigs. Reduced cortisol concentrations in response to high ambient temperatures have been reported in young pigs and sows (Kattesh et al., 1980; Heo et al., 2005). Those investigators have suggested that the lower cortisol concentrations following heat stress may be due to increased turnover of plasma cortisol, but since cortisol turnover rate was not measured here it is not possible to confirm this as a mechanism. Moreover, repeated exposure to the same stressor can cause a decrease in the responsiveness of, and even habituation of, the HPA axis to stress (Pitman et al., 1988). Such habituation may be due, in part, to alterations in the negative-feedback inhibition due to elevated glucocorticoid concentrations on the HPA axis in response to a chronic stressor (Jaferi et al., 2003). The disruption in the negative feedback loop is thought to involve downregulation of glucocorticoid receptors at the feedback sites of the brain (Mizoguchi et al., 2003); therefore, the lower cortisol concentrations observed in stressed pigs in this study may be reflective of alterations in the negative feedback of the HPA axis caused by 14 d of continuous exposure to heat and crowded conditions. Moreover, it is somewhat surprising that despite the differential baseline plasma cortisol concentrations between Meishans and other breeds in this study that there was no breed effect on cortisol response to stress. It is possible that breed differences would have been detected if cortisol was assessed at an earlier time point than 24 h posttreatment. Because cortisol concentrations generally peak at approximately 30 min after imposition of a stressor in pigs (Prunier et al., 2005), it is possible that breed effect on the cortisol response to these stressors could have occurred during the cortisol peak.

Immune measures in pigs are affected by various stressors, including heat exposure, social tension, and transportation. Baseline breed differences did exist for B- and T-cell lymphocyte proliferation and NK cytotoxicity; B- and T-cell-induced proliferation was lowest in Yorkshire pigs, and NK cytotoxicity was greater in Meishans. These findings are in accord with our previous findings (Sutherland et al., 2005) as well as those of Reed and McGlone (2000), who reported that 25% Meishan pigs had a 17% increase in NK activity compared with pigs of a commercial white line. Despite these breed differences in baseline B- and T-cell-induced proliferation and NK cytotoxicity, these immune responses to the 14-d multiple concurrent stressor used in this study did not differ among the breeds assessed. In the current study, both B-cell-induced lymphocyte proliferation and NK cytotoxicity were greater in stressed pigs than in their control counterparts at d 1 and 14 regardless of breed. Contrary to these findings, Hicks et al. (1998) reported no difference in phytohemagglutinin T-cell-induced lymphocyte proliferation between control pigs and those subjected to either cold, heat, or shipping for 4 h. In other work, NK cytotoxicity was elevated in pigs subjected to acute (4 h) cold stress but not in pigs exposed to 4 h heat or shipping stress (Hicks et al., 1998). Taken together, these results suggest that the B-cell proliferation and NK cytotoxicity responses to stress may depend on either duration or type of stressor used or both more so than breed. Also, the aspect of the immune response, specifically cell type, may be affected differently by the stressor imposed. More importantly, it is unclear whether increased lymphocyte proliferation and NK responses after exposure to a chronic stressor indicates altered disease susceptibility. Further research is needed to address these issues.

Social status can also influence many aspects of the immune response to different stressors (McGlone et al., 1993; Hicks et al., 1998; Tuchscherer et al., 1998). Social status affected several aspects of the innate immune response following 14 d of heat and crowding stress in this study. Consistently, pigs identified as being submissive had lower immunological responses to stressors than did their DOM counterparts. Social status of pigs exposed to the 14-d concurrent multiple stressor used in the current study greatly influenced total WBC counts. Stressed pigs identified as DOM had greater total WBC counts than did submissive pigs. Following 4 h of either acute shipping, cold, or heat stress, social status had no impact on total WBC, percentage differentials, or lymphocyte or neutrophil counts (Hicks et al., 1998). Likewise, following 28 d of heat stress, Morrow-Tesch et al. (1994) found no effect of social status on leukocyte counts. The differences between those and our present findings may be related to stressor duration, intensity, or both (acute vs. chronic stress), or type of stressor, such as antigenic, physiological, physical, or psychological. Although it is apparent that pig social status can be influential, caution nevertheless should be exercised when making generalizations about any impact of social status on the stress responsiveness of pigs.

Social status also influenced NK cytotoxicity and neutrophil PHAGO in stressed pigs; thus these responses were greater in DOM pigs than in those identified as SUB following the 14-d chronic stressor. Others have reported that NK cytotoxicity is greater in DOM pigs after 4 h of transport or cold stress than in submissive pigs (McGlone et al., 1993; Hicks et al., 1998). However, in pigs exposed to acute cold, heat, or shipping stress, social status did not affect the ability of neutrophils to engulf a foreign particle (Hicks et al., 1998), whereas NK cytotoxicity appears to be enhanced in DOM pigs after exposure to stress, regardless of type or duration of stressor. Pig social status appears to influence PHAGO in response to 14 d of heat and crowding but not in response to 4 h of acute stress. The social status of a pig appears to have an important influence on various aspects of the innate immune response to various stressors. Further research is needed to determine if DOM pigs, which have consistently greater immune status, are better able to cope with an antigenic challenge.

In the current study, a chronic 14-d multiple concurrent stressor consisting of heat and crowding affected pig performance and various physiological measures, but these effects were not influenced by pig breed. Importantly, social status had a larger impact on the physiological responses measured in response to stress than did pig breed. For instance, submissive pigs had suppressed total WBC, NK, and PHAGO compared with DOM pigs, regardless of breed. Therefore, despite the fact that pig breed influenced baseline immune and cortisol responses, such differences did not appear to reflect stress responsiveness as measured by innate immunity of a pig subjected to 7 or 14 d of heat and crowding. It would be of interest to determine if the decreased WBC count, PHAGO activity, and NK cytotoxicity observed in submissive pigs following 14 d of chronic stress is associated with those animals being more susceptible than either INT or DOM pigs to an antigenic challenge.

	Footnotes

 
¹ This research was supported by the Cargill Horizon Program, the Illinois Agricultural Experiment Station, and Sygen International. The authors thank M. J. Horseman, E. A. Hackerson, B. J. Peters, and K. Smith for their assistance.

² Corresponding author: johnso17{at}uiuc.edu

Received for publication June 28, 2005. Accepted for publication October 27, 2005.

	LITERATURE CITED

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 


Björk, A., N. G. Olsson, E. Christensson, K. Martinsson, and O. Olsson. 1988. Effects of amperozide on biting behavior and performance in restricted-fed pigs following regrouping. J. Anim. Sci. 66:669–675.

Blecha, F., and K. W. Kelley. 1981. Effects of cold and weaning stressors on the antibody-mediated immune responses of pigs. J. Anim. Sci. 53:439–447.

Desautes, C., A. Sarrieau, J. Caritez, and P. Mormede. 1999. Behavior and pituitary-adrenal function in large White and Meishan pigs. Domest. Anim. Endocrinol. 16:193–205.[Medline]

Fritschen, R. D., and A. J. Muehling. 1986. Space requirement for swine. Pork Industry Handbook, #55. Purdue Univ., West Lafayette, IN.

Heo, J., H. G. Kattesh, M. P. Roberts, J. L. Morrow, J. W. Dailey, and A. M. Saxton. 2005. Hepatic corticosteroid-binding globulin (CBG) messenger RNA expression and plasma CBG concentrations in young pigs in response to heat and social stress. J. Anim. Sci. 83:208–215.[Abstract/Free Full Text]

Hermann, G., C. A. Tovar, F. M. Beck, C. Allen, and J. F. Sheridan. 1993. Restraint stress differentially affects the pathogenesis of an influenza viral infection in 3 inbred strains of mice. J. Neuroimmunol. 47:83–94.[Medline]

Hicks, T. A., J. J. McGlone, S. C. Whisnant, H. G. Kattesh, and R. L. Norman. 1998. Behavioral, endocrine, immune, and performance measures for pigs exposed to acute stress. J. Anim. Sci. 76:474–483.[Abstract/Free Full Text]

Hyun, Y., M. Ellis, G. Riskowski, and R. W. Johnson. 1998. Growth performance of pigs subjected to multiple concurrent environmental stressors. J. Anim. Sci. 76:721–727.[Abstract/Free Full Text]

Jaferi, A., N. Nowak, and S. Bhatnagar. 2003. Negative feedback functions in chronically stressed rats: Role of the posterior para-ventricular thalamus. Physiol. Behav. 78:365–373.[Medline]

Jolie, R., L. Backstrom, L. Olson, and C. Chase. 1997. Respiratory and systemic health parameters in pigs raised in a conventional farm or in isolation. Swine Health Prod. 7:269–275.

Kattesh, H. G., E. T. Kornegay, J. W. Knight, F. G. Gwazdauskas, H. R. Thomas, and D. R. Notter. 1980. Glucocorticoid concentrations, corticosteroid binding protein characteristics and reproduction performance of sows and gilts subjected to applied stress during mid-gestation. J. Anim. Sci. 50:897–905.

Kornegay, E. T., M. D. Lindemann, and V. Ravindran. 1993a. Effects of dietary lysine levels on performance and immune response of weanling pigs housed at two floor space allowances. J. Anim. Sci. 71:552–556.[Abstract]

Kornegay, E. T., J. B. Meldrum, and W. R. Chickering. 1993b. Influence of floor space allowance and dietary selenium and zinc on growth performance, clinical pathology measurements and liver enzymes, and adrenal weights of weanling pigs. J. Anim. Sci. 71:3185–3198.[Abstract]

Lumpkin, E., and J. J. McGlone. 1992. A ⁵¹Cr release assay for the determination of natural killer cell activity. J. Nutr. Immunol. 61:63–74.

McGlone, J. J. 1985. A quantitative ethogram of aggressive and submissive behaviors in recently regrouped pigs. J. Anim. Sci. 61:559–565.

McGlone, J. J., and S. E. Curtis. 1985. Behavior and performance of weanling pigs in pens equipped with hide areas. J. Anim. Sci. 60:20–24.

McGlone, J. J., J. L. Salak-Johnson, E. A. Lumpkin, R. I. Nicholson, M. Gibson, and R. L. Norman. 1993. Shipping stress and social status effects on pig performance, plasma cortisol, natural killer cell activity, and leukocyte numbers. J. Anim. Sci. 71:888–896.[Abstract]

Mizoguchi, K., A. Ishige, M. Aburada, and T. Tabira. 2003. Chronic stress attenuates glucocorticoid negative feedback: Involvement of the prefrontal cortex and hippocampus. Neuroscience 119:887–897.[Medline]

Morrow-Tesch, J. L., J. J. McGlone, and J. L. Salak-Johnson. 1994. Heat and social stress effects on pig immune measures. J. Anim. Sci. 72:2599–2609.[Abstract]

Nguyen, V. P., C. W. Wong, G. N. Hinch, D. Singh, and I. G. Colditz. 1998. Variation in the immune status of two Australian pig breeds. Aust. Vet. J. 76:613–617.[Medline]

Nienaber, J. A., T. P. McDonald, G. L. Hahn, and Y. R. Chen. 1991. Group feeding behavior in swine. Trans. ASAE 34:289–294.

NRC. 1998. Nutrition Requirement of Swine. Natl. Acad. Press, Washington, DC.

Pitman, D. L., J. E. Ottenweller, and B. H. Natelson. 1988. Plasma corticosterone levels during repeated presentation of two intensities of restraint stress: Chronic stress and habituation. Physiol. Behav. 43:47–55.[Medline]

Prunier, A., A. M. Mounier, and M. Hay. 2005. Effects of castration, tooth resection, or tail docking on plasma metabolites and stress hormones in young pigs. J. Anim. Sci. 83:216–222.[Abstract/Free Full Text]

Reed, S. N., and J. J. McGlone. 2000. Immune status of PIC Camborough-15 sows, 25% Meishan sows, and their offspring kept indoors and outdoors. J. Anim. Sci. 78:2561–2567.[Abstract/Free Full Text]

Rosochacki, S. J., A. B. Piekarzewska, J. Poloszynowicz, and T. Sakowski. 2000. The influence of restraint immobilization stress on the concentration of bioamines and cortisol in plasma of Pie-train and Duroc pigs. J. Vet. Med. A. 47:231–242.

Salak, J. L., J. J. McGlone, and M. Lyte. 1993. Effects of in vitro adrenocorticotrophic hormone, cortisol and human recombinant interleukin-2 on porcine neutrophil migration and luminal-dependent chemiluminescence. Vet. Immunol. Immunopathol. 39:327–337.[Medline]

Sutherland, M. A., S. L. Rodriguez-Zas, M. Ellis, and J. L. Salak-Johnson. 2005. Breed and age affect baseline immune traits, cortisol and performance in growing pigs. J. Anim. Sci. 83:2087–2095.[Abstract/Free Full Text]

Tuchscherer, M., B. Puppe, A. Tuchscherer, and E. Kanitz. 1998. Effects of social status after mixing on immune, metabolic, and endocrine responses in pigs. Physiol. Behav. 64:353–360.[Medline]

Weiler, U., R. Claus, S. Schnoebelen-Combes, and I. Louveau. 1998. Influence of age and genotype on endocrine parameters and growth performance: A comparative study in wild boar, Meishan and Large White boars. Livest. Prod. Sci. 54:21–31.

Xin, H., and J. A. DeShazer. 1992. Feeding patterns of growing pigs at warm constant and cycle temperatures. Trans. ASAE 35:319–323.

This article has been cited by other articles:

				C. D. Reinhardt, W. D. Busby, and L. R. Corah Relationship of various incoming cattle traits with feedlot performance and carcass traits J Anim Sci, September 1, 2009; 87(9): 3030 - 3042. [Abstract] [Full Text] [PDF]

				M Sjolund, A. J. M. de la Fuente, C. Fossum, and P. Wallgren Responses of pigs to a re-challenge with Actinobacillus pleuropneumoniae after being treated with different antimicrobials following their initial exposure Vet Rec., May 2, 2009; 164(18): 550 - 555. [Abstract] [Full Text] [PDF]

				B. G. Kim, M. D. Lindemann, and G. L. Cromwell The effects of dietary chromium(III) picolinate on growth performance, blood measurements, and respiratory rate in pigs kept in high and low ambient temperature J Anim Sci, May 1, 2009; 87(5): 1695 - 1704. [Abstract] [Full Text] [PDF]

				M. Domingos, A. Amado, and A. Botelho IS1245 RFLP analysis of strains of Mycobacterium avium subspecies hominissuis isolated from pigs with tuberculosis lymphadenitis in Portugal Vet Rec., January 24, 2009; 164(4): 116 - 120. [Abstract] [Full Text] [PDF]

				J. D. Lippolis Immunological signaling networks: Integrating the body's immune response J Anim Sci, April 1, 2008; 86(14_suppl): E53 - E63. [Abstract] [Full Text] [PDF]

				J. L. Salak-Johnson and J. J. McGlone Making sense of apparently conflicting data: Stress and immunity in swine and cattle J Anim Sci, March 1, 2007; 85(13_suppl): E81 - E88. [Abstract] [Full Text] [PDF]

This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Sutherland, M. A. Articles by Salak-Johnson, J. L. Search for Related Content PubMed PubMed Citation Articles by Sutherland, M. A. Articles by Salak-Johnson, J. L.