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Effect of weaning age and commingling after the nursery phase of pigs in a wean-to-finish facility on growth, and humoral and behavioral indicators of well-being^1,2

Department of Animal Science, University of Arkansas, Fayetteville 72701

	Abstract

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
Pigs from one farrowing group in which gilts were bred to farrow pigs that would be either 14 or 21 d of age at weaning, were divided into older and younger age groups (108 pigs per group) and penned 12 pigs per pen in a wean-to-finish facility. At the end of the nursery phase, half the pigs in each age group were removed, rerandomized, and commingled for the finishing phase. The other half remained in their original pens. Pigs were fed common Phase 1 (d 0 to 14) and Phase 2 (d 14 to 35) nursery diets, and a common 4-phase program diet during growing/finishing, with transitions at 45, 68, and 90 kg of BW. The study ended when the lightest weight block averaged 107 kg. Blood was obtained on d 0, 2, 10, 27, 37, 44, and 65 after weaning to determine leukocyte concentrations. In addition, behavior was monitored during the nursery period at weaning (d 0), on d 7, 14, and 27 after weaning, and during the growing/finishing phase on d 35 (after commingling following the nursery phase), 38, 44, and 65 after weaning. Older pigs were heavier (P < 0.001) throughout the nursery period, and the BW difference between younger and older pigs increased from 2 to 6.5 kg at the start and end of the nursery period, respectively. Older pigs had a greater concentration of white blood cells (P < 0.05) and lymphocytes (P < 0.10) on d 0, 2, and 10 after weaning than younger pigs. Younger pigs spent less (P < 0.05) time resting on the day of weaning, and more (P < 0.05) time active during the overall nursery phase. During Phase 3 and in the overall finishing phase, younger pigs had greater (P < 0.01) ADG and G:F than older pigs. Moreover, during Phase 3, ADFI (as fed) decreased (P < 0.05) when older pigs were commingled compared with older pigs that were not commingled. There was no difference in ADFI of younger pigs, regardless of commingling (interaction; P < 0.10). Results of this study indicate that weaning age affects growth performance in a wean-to-finish facility, as well as behavioral and immunological responses to weaning and commingling after the nursery phase. Management strategies should be further explored to optimize these benefits without the detrimental effects on health observed during the nursery period in this study.

Key Words: behavior • growth • immune response • mixing • swine • weaning

	INTRODUCTION

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
Pigs born and raised in conventional swine production systems are routinely weaned as early as 17 d of age and as early as 12 to 14 d of age in off-site segregated early weaning systems (Maxwell and Carter, 2000). Although there are no legislative restrictions on weaning age in the United States, the practice of weaning before 28 d of age is prohibited in Europe (ECCD, 2001). Early weaning and removal of pigs to a second isolated site for rearing can decrease the potential for disease transfer from the dam (Harris, 1988). Pigs reared in isolation after weaning have decreased immunological stress (Johnson, 1997), resulting in substantial improvements in growth and efficiency of feed use compared with those reared in conventional farrow-to-finish systems (Williams et al., 1997). Similarly, commingling pigs following the nursery phase is a common management practice in the swine industry, and it imposes an additional stress on the young pig. The advent of wean-to-finish facilities has potentially alleviated commingling after the nursery phase; however, the wasted space of placing weanling pigs in pens with space allowances for market hogs has led to the practice of double-stocking pens at weaning and later moving half the pigs to another pen, which introduces a commingling stress at an older age (Wolter et al., 2002). Results supporting wean-to-finish production systems with regard to piglet well-being are lacking, and the effect of these systems on pig health has not been evaluated. Therefore, the objective of this study was to determine the effect of age at weaning and of rearing pigs in the same pen in an all-in–all-out wean-to-finish facility vs. commingling pigs after the nursery phase on growth performance and on humoral and behavioral indicators of well-being.

	MATERIALS AND METHODS

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
Allocation of Animals
Pigs from one farrowing of 30 litters (DeKalb Line 348 gilts mated to EB sires; Monsanto Choice Genetics, St. Louis, MO) over a 10-d period were weaned when the average age was approximately 17 ± 0.3 d. Gilts were bred to farrow pigs that would average 14 and 21 d of age when weaned on the same day. Gilts were farrowed in crates in an environmentally controlled farrowing room. Immediately after farrowing, pigs were ear-notched for individual identification, administered iron dextran, and tails were docked. Pigs were cross-fostered if necessary to equalize litters within their respective age groups. Pigs were divided into 2 age groups of equal number representing the older (21 d of age) and younger (14 d of age) groups of pigs (108 pigs in each group). Pigs within each age group were sorted into 3 blocks based on BW and gender (36 pigs per block). Pigs from each gender and BW category within age group were then allocated randomly to pens within block in a double-stocked wean-to-finish facility (12 pigs per pen). This provided a total of 9 replications of each age group for the nursery study. At the completion of the nursery phase, half the pigs in each age category were removed from the double-stocked pens, rerandomized based on gender and BW, and commingled for the growing-finishing component of the study. Half the pigs remained in the same wean-to-finish pens. This arrangement of treatments permitted evaluation of the effects of weaning age in pigs double-stocked in a wean-to-finish facility, as well as effects of postnursery commingling on well-being and performance.

Housing and Environment
Pigs were housed in a wean-to-finish facility in totally slatted pens (1.52 m x 3.05 m; 0.39 m²/pig) equipped with radiant heaters, a 2-hole nursery feeder, and a wean-to-finish cup waterer. Ambient room temperature was maintained at 25.6°C. In addition, a radiant heater oriented above rubber mats provided supplemental heat to a 1.8-m diameter area covering 2 pens per heater during the nursery phase. Wean-to-finish barns were curtain-sided and naturally ventilated, and contained a pit fan. Temperature was decreased gradually over the course of the nursery phase according to established procedures (no more than 1.5°C/wk). The temperature was maintained at approximately 21.1°C throughout the starter and grower I phases, and decreased to 20°C during the grower II and finisher phases. Water and feed were available ad libitum throughout the study.

Experimental Management
On the day of weaning, pigs were moved from the farrowing room and distributed to their assigned pen. Pigs were exposed to natural lighting, with supplemental electrical lighting provided only when animals were being observed. Pigs were offered ad libitum access to a Phase I nursery diet for the period of 0 to 14 d and a Phase II diet for the period of 14 to 35 d (Table 1). On the day of completion of the nursery phase of the study, pigs were started on the growing-finishing study. Pigs were fed a 4-phase diet with transition from starter to grower I, grower I to grower II, and grower II to finisher occurring when the mean BW of each block reached approximately 45, 68, and 90 kg, respectively (Table 2). All diets met or exceeded NRC (1998) requirements for all nutrients, and were formulated to simulate diets typical of those used in the swine industry. The study ended when the lightest block reached an average BW of 107 kg. The experiment was carried out in accordance with the Animal Care Protocol No. 01015 for swine experiments issued by the University of Arkansas Institutional Animal Care and Use Committee.

Physiological Measures
A 5-mL blood sample was obtained from each pig via venipuncture on d 0, 2, 7, 13, 27, 37, 42, and 56. Blood samples were kept on ice for transport approximately 24 km from the University of Arkansas Swine Research Unit to laboratory facilities at the University of Arkansas Animal Science Department. Blood measurements of interest (differential leukocyte proportions and neutrophil:lymphocyte ratio) were obtained by analysis on an automated hematology analyzer (Cell-Dyn 3500SL System; Abbott, Abbott Park, IL) calibrated for porcine blood. An additional 15-mL blood sample was obtained on d 8 of the nursery period from 4 pigs randomly selected from 3 pens from each age group, and peripheral blood mononuclear cells were isolated to determine lymphocyte blastogenic response, interferon-gamma (IFN-) production, and macrophage phagocytosis. This procedure was repeated on d 10 and 12 for the remaining 6 pens in each age group. Data from the 3 sampling days were pooled and designated as d 10 after weaning. The same process was repeated postnursery for all pens, with 2 randomly chosen pigs per pen sampled, and pooled data were designated as d 44 after weaning.

Lymphocyte Blastogenesis.
In vitro cellular proliferative response was measured using a lymphocyte blastogenesis assay adapted from the methods of Blecha et al. (1983). Briefly, peripheral blood mononuclear cells were isolated by gradient centrifugation using a Ficoll gradient (Histopaque 1077, density = 1.077 g/mL; Sigma Chemical Co., St. Louis, MO). Remaining erythrocytes were lysed by adding 1 mL of sterile water to the isolated cell pellet for 20 s, and isotonicity was restored by the addition of Roswell Park Memorial Institute medium (RPMI; Sigma). Cells were resuspended in RPMI at 2 x 10⁶ cells/mL, and plated in triplicate in 96-well round bottom plates in 100-µL aliquots. Phytohemagglutinin (PHA; Sigma), pokeweed mitogen (PWM; Sigma), and concanavalin A (ConA; Sigma) were administered in 50-µL aliquots to each well at a concentration of 40, 15, and 25 µg/mL, respectively, to stimulate lymphocyte proliferation, whereas wells containing cells unstimulated with mitogen were administered 50 µL of medium. Concentrations chosen for each respective mitogen elicited the maximum proliferative response during preliminary trials. Cells were incubated with the mitogens for 48 h at 39.2°C and 5% CO₂. The incubation temperature for all assays conducted in this study was set at 39.2°C rather than 37°C, to facilitate monocyte/macrophage activation under conditions simulating pig body temperature (Natale and McCullough, 1998). Following the 48-h incubation, 1 µCi of tritiated thymidine in 50 µL of RPMI was added to each well, and the cells were incubated for an additional 18 h. Cells were harvested on glass fiber mats and the radioactivity was measured on a liquid scintillation analyzer (TRI-CARB 2200CA; Packard Instrument Co., Downers Grove, IL). Incubation, labeling with tritiated thymidine, and cell harvesting followed procedures outlined by van Heugten et al. (1994).

Interferon- Production.
Peripheral blood mononuclear cells were isolated as described for the lymphocyte blastogenesis assay. Cells were dispensed in duplicate at a concentration of 2 x 10⁶ cells/mL in 500-µL aliquots into a 24-well plate. An additional 500 µL of RPMI was added to one of the duplicated wells, and 500 µL of RPMI containing 10 µg/mL of ConA was added to the second well, for unstimulated and stimulated cultures, respectively. Cell cultures were incubated for 48 h at 39.2°C and 5% CO₂. Following the 48-h incubation, supernatant fractions were collected from each well and stored at –20°C until analysis for IFN- could be conducted. Interferon- production was determined using a swine IFN- ELISA kit following the instructions provided by the manufacturer (Biosource International Inc., Camarillo, CA). The intraassay CV was 17.5%.

Monocyte/Macrophage Phagocytosis.
The method used to measure monocyte/macrophage phagocytic ability of peripheral blood monocytes was adapted from the methods of Nibbering et al. (1987), Heggen et al. (1998), and Monteleone et al. (1999). Peripheral blood mononuclear cells from blood were isolated as described for the lymphocyte blastogenesis assay. Cell suspensions isolated from blood were diluted to approximately 5 x 10⁶ cells/mL in LM Hahn (Leibovitz’s L-15/McCoy’s Hahn media; Atlanta Biologicals, Lawrenceville, GA) medium. A glass coverslip was added to each well of a 6-well plate, and 2 mL of cell suspension containing monocytes/macrophages was added to each well in duplicate for each sample. Each coverslip was completely covered by cell suspension. Cells were incubated for 5h at 39.2°C and 5% CO₂. Following the 5-h incubation, medium from each well was removed and replaced by 2 mL of fresh LM Hahn medium warmed to 39.2°C. Cell cultures were incubated for an additional 19 h. Following the 24-h total incubation, plates were removed from the incubator, excess medium was removed from each well, and 2 mL of a 4% sheep red blood cell (SRBC) suspension were added to each well. Plates were incubated with SRBC for 2 h, after which coverslips were removed, and nonadherent cells and excess SRBC were washed from the coverslip by rinsing with LM Hahn medium warmed to 39.2°C. Coverslips were then stained using the Hema 3 cell staining kit (Fisher Scientific, Pittsburgh, PA), and the percentage of phagocytic monocytes/macrophages and the average number of SRBC consumed by each phagocytic monocyte/macrophage were determined.

Performance Measures
Pigs were weighed as each block reached the projected BW for each phase. Pig BW was averaged by pen and ADG was calculated. Feed disappearance from each pen self-feeder was measured and ADFI (as fed) was calculated for each pen as the difference between feed added and feed weighed back for each period, and G:F ratios for each period were determined. Adjusted days to a common BW (104 kg) were calculated for each pig using the following formula: (age of pig at the time final BW was obtained + [desired final BW – actual BW]{[age –38]/actual BW}; NSIF, 2002).

Experimental Design
Performance and behavioral data were analyzed as a randomized complete block design in a 2 x 2 factorial arrangement of treatments, with 2 weaning ages and 2 postnursery management systems, pen as the experimental unit, and day of observation as a repeated measure using PROC MIXED of SAS (SAS Inst., Inc., Cary, NC). When significant day x treatment interactions were observed, ANOVA for each day was performed using PROC GLM of SAS. Mortality rate was analyzed by ² analysis in SAS.

	RESULTS

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
Behavioral Measures
Pigs weaned at 21 d of age spent a greater (P < 0.05) percentage of time resting on the day of weaning (d 0 postweaning) than pigs weaned at 14 d of age (Table 4). Although the percentage of time spent active did not differ between pigs of different weaning ages at any observation day during the nursery period, pigs weaned at 14 d of age spent a greater (P = 0.05) proportion of time active during the overall nursery phase than did pigs weaned at 21 d of age (Table 5). There was no difference in the percentage of time that pigs weaned at either age were engaged in aggressive behavior on any of the sampling days, but the frequency of times aggressive behaviors were observed was greater (P < 0.05) at weaning (d 0) than on any other observation day during the nursery period (Figure 1). Very few incidents of belly-nosing by pigs were observed in this study, and number and duration of belly-nosing incidents did not differ between older and younger pigs.

View larger version (6K): [in this window] [in a new window]   Figure 1. Frequency of aggressive behaviors observed on each day of the nursery phase. Bars with an asterisk differ from those without asterisks, P < 0.05.

View larger version (27K): [in this window] [in a new window]   Figure 2. Percentage of time spent engaged in feeding behavior during the growing/finishing phase by pigs weaned at either 14 or 21 d of age and either commingled (mixed) following the nursery or remained in original pens (weaning age x mixing x date interaction; P < 0.05). Within a specific day after weaning, bars with an asterisk differ from those without asterisks, P < 0.05.

View this table: [in this window] [in a new window]   Table 13. Effect of age at weaning on macrophage phagocytic capacity, lymphocyte proliferation response, and interferon- production of pigs during the nursery phase1

View larger version (11K): [in this window] [in a new window]   Figure 3. Effect of mixing and age at weaning on ADFI (as fed) of pigs during Phase 3 of the growing/finishing period (interaction; P = 0.08). Bars that do not have a common letter differ, P < 0.05.

	DISCUSSION

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

The incidence of belly-nosing was not affected by age of pigs at weaning in this study, although many studies have reported a greater incidence of belly-nosing when pigs were weaned at 14 d of age (Metz and Gonyou, 1990; Gonyou et al., 1998, Worobec et al., 1999). Nonetheless, the observation times in this study may have overlooked aberrant behaviors that occurred in either age group. Moreover, there was no evidence of lesions present on pigs because of repetitive belly-nosing behavior, indicating that belly-nosing activity was likely minimal.

During the growing-finishing period, differences in the percentage of time spent engaged in feeding behavior during the growing/finishing period depended on the age of pigs at weaning, whether pigs were commingled after the nursery period, and the time after commingling occurred. Commingling decreased the percentage of time pigs engaged in feeding behavior directly after the commingling event for both age groups. This finding suggests that reestablishment of the social structure within pens was necessary when pigs were regrouped. This response was transient, with no observed differences in duration of feeding behavior in the days following the initial postnursery commingling, except on d 65 after weaning. Similarly, other research has reported that altered or agnostic behaviors were present only during a short time after the commingling stress (McGlone et al., 1987; Heetkamp et al., 1995). We have no explanation, however, for the observations on d 65 after weaning, in which pigs weaned at 21 d of age and mixed, and pigs weaned at 14 d of age and remained unmixed spent a greater percentage of time engaged in feeding behavior. However, the observations coincided with the beginning of the phase 2 period in which feed intake and gain by pigs weaned at 14 d of age began to increase during the growing/finishing period.

Physiological Measures
Total WBC concentrations of pigs in this experiment were lower than values reported previously in the literature (Schmidt and Tumbleson, 1986; Kleinbeck and McGlone, 1999); however, proportions of individual leukocyte populations were within expected ranges (Duncan and Prasse, 1986; Schmidt and Tumbleson, 1986). The low concentration of WBC was surprising with the increased mortality observed due to Streptococcus suis infection, particularly in the young age group, as a disease challenge would be expected to raise leukocyte concentrations in the blood. Concentrations of total WBC vary depending on genetics, rearing environment, and health status within a herd (Schmidt and Tumbleson, 1986), and the discrepancy between total WBC values reported in this study and those reported previously is likely a reflection of these differences. Although differences in the concentrations of neutrophils and lymphocytes were detected between the two age groups, the percentage of these cells and the neutrophil:lymphocyte ratio did not differ, suggesting that the observed differences were likely age-related and not altered due to differing responses to the stress of weaning. Whereas the emphasis in this study was on differences in the neutrophil:lymphocyte ratio as a measure of stress, the differences in concentrations and percentages of eosinophils on the various sampling days between treatment groups may provide insight into the pigs’ immunological response to the stress of weaning and commingling. Eosinophils decrease in response to stress (Dvorak, 1968; Schmidt and Tumbleson, 1986), and the changes in this cell population in response to stress warrant further investigation.

White blood cell concentrations in this study were similar between younger and older pigs on d 27 after weaning, indicating the younger pigs may be advancing in their immunological development; however, younger pigs were less immunologically responsive to the stress of mixing and resorting after the nursery phase than older pigs, as indicated by the interaction of weaning age and mixing treatment observed 3 d after commingling. White blood cell concentrations of older pigs that were commingled were greater compared with older pigs that remained in their original pens, whereas WBC concentrations of younger pigs did not differ in response to the commingling treatment. Although young pigs did not respond immunologically to commingling, the difference in the percentage of time engaged in feeding behavior was very pronounced between mixed and unmixed pigs weaned at 14 d of age, indicating that young commingled pigs greatly reduced feeding behavior in response to commingling compared with young, unmixed pigs.

Physiological responses to stress and behavior involve complex interactions of the central nervous system, the endocrine system, and the immune system (Yang and Glaser, 2000), and these systems all influence health and well-being in response to environmental and management conditions. In an experiment evaluating the effects of stress at birth on cortisol concentrations, pigs responded to stress associated with a caesarean-section birth with increased serum cortisol, although this increase was not associated with a resulting increase in ACTH, suggesting a disregulation of ACTH and cortisol in caesarean-derived pigs (Daniel et al., 1999). Hohenshell et al. (2000) reported a similar disregulation of the hypothalamic-pituitary-adrenal axis between the pituitary and adrenal glands in early-weaned pigs that was not present in late-weaned pigs. Although not directly correlated with the sensitivity of the immune system in response to stressors, this disregulation of endocrine function could be a cause of the inability of early-weaned pigs to respond immunologically to the mixing and resorting stress during the postnursery period in the current study.

Performance Measures
The lower growth rate during the nursery period of pigs weaned at 14 d of age compared with older pigs is in contrast to other studies that reported either an improvement in ADG of early-weaned (10 d) pigs compared with late-weaned (30 d) pigs (Hohenshell et al., 2000) or no effect of weaning age on rate of the growth in the overall nursery period (Dritz et al., 1996). Although Hohenshell et al. (2000) reported greater ADG by early-weaned pigs at 42, 65, and 102 d of age compared with late-weaned pigs, early-weaned pigs were fed a nutrient-rich starter diet until the late-weaned pigs were moved into the nursery, which may have altered their subsequent performance compared with older pigs. Because gilts in the current study were bred in the same breeding group to farrow pigs that would average either 14 or 21 d at weaning, pigs were weaned on the same day to the same wean-to-finish facility and fed the same diet. Thus, the effect of weaning age should not be confounded by health status of the sow herd, environmental conditions, or management practices. To our knowledge, this is the first experiment to report that early-weaned pigs overcame a deficit in BW at the end of the nursery period to reach a common BW in fewer days than pigs weaned at 21 d of age. Others have reported no effect of weaning age when evaluating overall gain from birth to market weight (Hohenshell et al., 2000), no difference in BW when comparing early- and late-weaned pigs at a common age (Dritz et al., 1996), or increases in ADG during the nursery and growing/finishing phases with increasing weaning age from 12 to 21.5 d of age (Main et al., 2004).

The difference in mortality between the young and old pigs during the nursery period is interesting to note, and it supports the immune suppression reported previously in pigs weaned at 2 to 3 wk of age (Blecha et al., 1983). Of the pigs that died during the nursery phase, all exhibited signs of Streptococcus suis, and the majority was pigs weaned at 14 d of age. Pigs weaned at a younger age, likely had a less developed, more naive immune system that was unable to respond to the disease challenge. This idea is supported by the greater concentration of WBC observed in older pigs than in younger pigs initially at weaning, as well as on d 2 and 10 after weaning.

General Discussion
Whereas the results of this study show that management conditions perceived as stressors, in this case, weaning and commingling pigs after the nursery period, elicit changes in WBC populations and influence behavior, there is no indication that any one measure of the immune response or behavior can quantify well-being in pigs. Although there was a tendency for commingled pigs to have greater concentrations of neutrophils, older pigs that were commingled also responded with elevated concentrations of lymphocytes; however, this immune response could not be associated with growth performance or any aggressive behavior observations. A stress-associated increase in cortisol can result in an alteration of blood leukocyte concentrations, specifically an increase in neutrophils and a concomitant decrease in lymphocytes in the peripheral blood that would result in an increase in the neutrophil-to-lymphocyte ratio in the stressed animal (Gross and Siegel, 1983; McGlone et al., 1993). In the current study, the neutrophil-to-lymphocyte ratio was similar among pigs regardless of weaning age or mixing treatment; however, the nonsignificant increase in the concentration and percentage of monocytes in response to mixing on d 37 (2 d following the commingling event) is interesting. To further compound the difficulty in measuring the immune response or behavior as indications of welfare, there were very few differences in behavioral responses between pigs weaned at different ages or between pigs commingled after the nursery phase and those that remained unmixed, and immune responses were inconsistent depending on the age of the pig at weaning. Although the results of this study raise interesting questions about the effect of management environments and stressors on pigs weaned at varying ages on subsequent performance and health, no single measure of growth performance, immunity, or behavior was found to conclusively measure a pig’s welfare in response to wean-to-finish management schemes.

In conclusion, results of this study indicate that weaning age affects growth performance in a wean-to-finish facility, as well as behavioral and immunological responses to weaning and commingling after the nursery phase. This study did not allow, however, for determination of the physiological changes in response to weaning at different ages that altered these behavioral and immunological measurements. Therefore, physiological responses and management strategies should be further explored to better understand the benefits and detriments of early weaning in wean-to-finish facilities.

	Footnotes

 
¹ Research funded by a grant from the National Pork Board, Des Moines, IA.

² The authors acknowledge the following Univ. Arkansas staff and students for their assistance with this project: T. Wistuba, A. Hays, B. Hinson, C. Bradley, C. Scarborough, B. Scarborough, M. Curran, R. Harmon, and M. Dirain.

³ Current address: Agtech Products, Inc. W227 N752 Westmound Dr., Waukesha, WI 53186 (phone: 262-521-1717; fax: 262-521-2442; e-mail: edavis{at}agtechproducts.com).

⁴ Corresponding author: japple{at}uark.edu

Received for publication September 27, 2004. Accepted for publication August 10, 2005.

	LITERATURE CITED

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 


Blecha, F., D. S. Pollmann, and D. A. Nichols. 1983. Weaning pigs at an early age decreases cellular immunity. J. Anim. Sci. 56:396–400.[Abstract/Free Full Text]

Daniel, J. A., D. H. Keisler, J. A. Sterle, R. L. Matteri, and J. A. Carroll. 1999. Birth by caesarian section alters postnatal function of the hypothalamic-pituitary-adrenal axis in young pigs. J. Anim. Sci. 77:742–749.[Abstract/Free Full Text]

Dritz, S. S., K. Q. Owen, J. L. Nelssen, and R. D. Goodband. 1996. Influence of weaning age and nursery diet complexity on growth performance and carcass characteristics and composition of high-health status pigs from weaning to 109 kilograms. J. Anim. Sci. 74:2975–2984.[Abstract]

Duncan, J. R., and K. W. Prasse. 1986. Veterinary Laboratory Medicine. 2nd ed. Iowa State Univ. Press, Ames.

Dvorak, M. 1968. The effect of traumatic stress on the leucocyte blood picture in the course of the postnatal development of piglets. Acta Univ. Agric. Fac. Vet. 37:537–544.

ECCD. 2001. European Community Commission Directive 2001/93/EC of 9 November 2001 amending Directive 91/630/EEC laying down minimum standards for the protection of pigs. Off. J. L 316:P0036–0038.

Fraser, D. 1978. Observations on the behavioural development of suckling and early-weaned piglets during the first six weeks after birth. Anim. Behav. 26:22–30.

Gardner, J. M., C. F. M. De Lange, and T. M. Widowski. 2001. Belly-nosing in early-weaned piglets is not influenced by diet quality of the presence of milk in the diet. J. Anim. Sci. 79:73–80.[Abstract/Free Full Text]

Gonyou, H. W., E. Beltranena, D. L. Whittington, and J. F. Patience. 1998. The behaviour of pigs weaned at 12 and 21 days of age from weaning to market. Can. J. Anim. Sci. 78:517–523.

Gross, W. B., and H. S. Siegel. 1983. Evaluation of the heterophil/lymphocyte ratio as a measure of stress in chickens. Avian Dis. 27:972–979.[Medline]

Harris, D. L. 1988. Alternative approaches to eliminating endemic diseases and improving performance of pigs. Vet. Rec. 123:422–423.[Medline]

Heetkamp, M. J. W., J. W. Schrama, L. de Jong, J. W. G. M. Swinkels, W. G. P. Shouten, and M. W. Bosch. 1995. Energy metabolism in young pigs as affected by mixing. J. Anim. Sci. 73:3562–3569.[Abstract]

Heggen, C. L., M. A. Qureshi, F. W. Edens, H. J. Barnes, and G. B. Havenstein. 1998. Alterations in the lymphocytic and mononuclear phagocytic systems of turkey poults associated with exposure to poult enteritis and mortality syndrome. Avian Dis. 42:711–720.[Medline]

Higgins, R., and M. Gottschalk. 1999. Streptococcal diseases. Pages 565–566 in Diseases of Swine. 8th ed. B. E. Straw, S. D’Allaire, W. L. Mengelng, and D. J. Taylor, ed. Blackwell Science, Malden, MA.

Hohenshell, L. M., J. E. Cunnick, S. P. Ford, H. G. Kattesh, D. R. Zimmerman, M. E. Wilson, R. L. Matteri, J. A. Carroll, and D. C. Jr. Jay. 2000. Few Differences found between early- and late-weaned pigs raised in the same environment. J. Anim. Sci. 78:38–49.[Abstract/Free Full Text]

Johnson, R. W. 1997. Explanation for why sick pigs neither eat well nor grow well. Page 49 in Proc. Carolina Swine Nutr. Conf., Research Triangle Park, NC.

Kleinbeck, S. N., and J. J. McGlone. 1999. Intensive indoor verses outdoor swine production systems: Genotype and supplemental iron effects on blood hemoglobin and selected immune measures in young pigs. J. Anim. Sci. 77:2384–2390.[Abstract/Free Full Text]

Maxwell, C. V., and S. D. Carter. 2000. Feeding the Weaned Pig. Page 692 in Swine Nutrition. A. J. Lewis and L. L. Southern, ed. CRC Press, Boca Raton, FL.

Main, R. G., S. S. Dritz, M. D. Tokach, R. D. Goodband, and J. L. Nelssen. 2004. Increasing weaning age improves performance in a multisite production system. J. Anim. Sci. 82:1499–1507.[Abstract/Free Full Text]

McGlone, J. J. 1986. Agnostic behavior in food animals: Review of research and techniques. J. Anim. Sci. 62:1130–1139.[Abstract/Free Full Text]

McGlone, J. J., J. L. Salak, 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]

McGlone, J. J., W. F. Stansbury, and L. F. Tribble. 1987. Effects of heat and social stressors and within-pen weight variation on young pig performance and agnostic behavior. J. Anim. Sci. 65:456.[Abstract/Free Full Text]

Metz, J. H. M., and H. W. Gonyou. 1990. Effect of age and housing conditions on the behavioural and haemolytic reaction of piglets to weaning. Appl. Anim. Behav. Sci. 27:299–309.

Monteleone, G., T. Parrello, I. Monteleone, S. Tammaro, F. Luzza, and F. Pallone. 1999. Interferon-gamma (IFN-) and prostaglandin E2 (PGE2) regulate differently IL-12 production in human intestinal lamina propria mononuclear cells (LPMC). Clin. Exp. Immunol. 117:469–475.[Medline]

Natale, V. A. I., and K. C. McCullough. 1998. Macrophage culture: Influence of species-specific incubation temperature. J. Immunol. Methods 214:165–174.[Medline]

Nibbering, P. H., P. C. J. Leijh, and R. Van Furth. 1987. Quantitative immunocytochemical characterization of mononuclear phagocytosis. II. Monocytes and tissue macrophages. Immunology 62:171–176.[Medline]

NRC. 1998. Nutrient Requirements of Swine. 10th ed. Natl. Acad. Press, Washington, DC.

NSIF. 2002. National Swine Improvement Federation. Guidelines for Uniform Swine Improvement Programs. III. On-Farm Programs. Online. Available: www.nsif.com/guidel/ONFARM.HTM Accessed June 3, 2004.

Schmidt, D. A., and M. E. Tumbleson. 1986. Swine hematology. Page 776–779 in Swine in Biomedical Research. M. E. Tumbleson, ed. Plenum Press, New York, NY.

van Heugten, E., J. W. Spears, and M. T. Coffey. 1994. The effect of dietary protein on performance and immune response in weanling pigs subjected to an inflammatory challenge. J. Anim. Sci. 72:2661–2669.[Abstract]

Williams, N. H., T. S. Stahly, and D. R. Zimmerman. 1997. Effect of chronic immune system activation on the rate, efficiency, and composition of growth and lysine needs of pigs fed from 6 to 27 kg. J. Anim. Sci. 75:2463.[Abstract/Free Full Text]

Wolter, B. F., M. Ellis, J. M. DeDecker, S. E. Curtis, G. R. Hollis, R. D. Shanks, E. N. Parr, and D. M. Webel. 2002. Effects of double-stocking and weighing frequency on pig performance in wean-to-finish production systems. J. Anim. Sci. 80:1442–1450.[Abstract/Free Full Text]

Worobec, E. K., I. J. H. Duncan, and T. M. Widowski. 1999. The effects of weaning at 7, 14, and 28 days on piglet behavior. Appl. Anim. Behav. Sci. 62:173–182.

Yang, E. V., and R. Glaser. 2000. Stress-induced immunomodulation: Impact on immune defenses against infectious disease. Biomed. Pharmacother. 54:245–250.[Medline]

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