Effects of environmental enrichment on behavioral responses to novelty, learning, and memory, and the circadian rhythm in cortisol in growing pigs

Previously we showed that pigs reared in an enriched environment had higher baseline salivary cortisol concentrations during the light period than pigs reared under barren conditions. In the present experiment, it was investigated whether these higher baseline salivary cortisol concentrations were a real difference in cortisol concentration or merely represented a phase difference in circadian rhythm. The effects of different cortisol concentrations on the behavioral responses to novelty and learning and long-term memory in a maze test were also studied in enriched and barren housed pigs. At 9 weeks of age enriched and barren housed pigs did not differ in baseline salivary cortisol concentrations nor in circadian rhythm, but at 22 weeks of age barren housed pigs had a blunted circadian rhythm in salivary cortisol as compared to enriched housed pigs. The differences in baseline salivary cortisol concentrations between enriched- and barren-housed pigs are age-dependent, and become visible after 15 weeks of age. Enriched- and barren-housed piglets did not differ in time spent on exploration in the novel environment test. Barren-housed pigs had an impaired long-term memory in the maze test compared to enriched-housed pigs; however, no differences in learning abilities between enriched- and barren-housed pigs were found. Because blunted circadian cortisol rhythms are often recorded during states of chronic stress in pigs and rats or during depression in humans, it is suggested that the blunted circadian rhythm in cortisol in barren-housed pigs similarily may reflect decreased welfare.     

Experimental infection of pigs with the newly identified swine hepatitis E virus (swine HEV), but not with human strains of HEV

Summary.  A novel virus of pigs, swine hepatitis E virus (swine HEV), was recently identified and shown to be antigenically and genetically related to human HEV. In the present study, we attempted to infect specific-pathogen-free (SPF) pigs experimentally with swine HEV or with human strains of HEV. Serum samples collected from naturally infected pigs were used as the source of swine HEV. Pigs inoculated intravenously with serum samples containing swine HEV seroconverted to anti-HEV 4 to 8 weeks postinoculation, and the virus spread to an uninoculated pig. Swine HEV was detected in nasal and rectal swab materials as early as 2 weeks postinoculation and for 4 to 8 weeks thereafter. Viremia appeared 4 to 6 weeks postinoculation and lasted 1 to 3 weeks. The inoculated pigs appeared clinically normal and serum liver enzymes were not significantly elevated. In contrast, pigs were not infected when inoculated intravenously with about 10⁵ monkey infectious doses of one of two human strains of HEV (Sar-55 or Mex-14). Received December 9, 1997 Accepted February 18, 1998     

Social buffering of the cortisol response of adult female guinea pigs

When housed in spacious, mixed age/sex colonies, male guinea pigs form small harems of females with which attachment-like social bonds are established. A previous study indicated that the bonded male, but not an unfamiliar male from the same colony, could reduce the plasma cortisol response of a female when exposed to a novel environment. We examined the effect of several classes of social partners on the cortisol response of females maintained under standard laboratory housing conditions. Eight "artificial harems" comprised of one adult male and two adult females were formed in standard group-housing cages 2 weeks prior to the study. Behavior observed in these home cages indicated that interactions between males and females of the triads were overwhelmingly positive in nature. When exposed to a novel environment for 2 h, the presence of either the male or female cage mate reduced the subject female's plasma cortisol response, whereas the presence of an unfamiliar adult male did not. Changes in plasma cortisol levels were not predicted by the frequency of various social behaviors observed in the novel environment. These findings: (1) demonstrate that the buffering effect of male partners on the cortisol response of adult females can be observed in guinea pigs maintained in conventional laboratory housing; (2) indicate that unfamiliar adult males are ineffective at reducing cortisol responses of females under these conditions; and, (3) appear to be the first to show buffering effects by adult female guinea pigs on the cortisol responses of other adult females.     

Similar hormonal changes in sera from scorbutic and fasted (vitamin C-supplemented) guinea pigs, including decreased IGF-I and appearance of an IGF-I reversible mitogenic inhibitor

We previously proposed that the decreased rates of synthesis of collagen and proteoglycans in vitamin C-deficient guinea pigs were unrelated to the role of ascorbate in proline hydroxylation but might result from modulation of hormones known to change during fasting. In the present studies, we found that sera from guinea pigs on an ascorbate-free diet for 24-28 days or from those fasted for 4 days, with vitamin C supplementation, showed similar changes in the concentrations of several hormones. EGF and IGF-II concentrations were unchanged, but cortisol was increased 3-5 times and growth hormone was increased to approximately twice normal levels. Thyroxine and IGF-I concentrations were decreased to 40% and 25-33% of normal levels, respectively. The decrease in serum IGF-I must occur by a growth hormone-independent pathway. The extent of changes in hormone concentrations in sera from ascorbate-deficient guinea pigs was correlated with the extent of weight loss. Sera from scorbutic and fasted guinea pigs failed to stimulate DNA synthesis in quiescent BALB 3T3 cells in the presence of saturating concentrations of EGF and PDGF. Addition of experimental sera to normal serum showed that lack of mitogenic activity was due to the presence of an inhibitor. Inhibition was not related to IGF-I concentrations in the sera, although it was reversed by the addition of IGF-I to sera from scorbutic or fasted animals. These results support our proposed model and suggest that IGF-I, as well as an inhibitor of its activity, plays a role in the regulation of growth by vitamin C and other nutrients.     

Lack of effect of metyrapone and exogenous cortisol on early porcine conceptus development

A study was conducted to evaluate the influence of maternal cortisol on early conceptus development in pigs (Sus scrofa). The corticosteroid synthesis inhibitor metyrapone was injected daily during days 14-19 of pregnancy, without (n = 6) and with commensurate administration of cortisol (n = 6). Blood samples were taken via an indwelling jugular catheter on days 14 and 18, and conceptuses were harvested during surgery on day 20. Compared with vehicle-injected control dams (n = 7) plasma cortisol and aldosterone concentrations were decreased (P < 0.01) by 52 and 29%, respectively, by metyrapone treatment. Cortisol administration reversed decreases in plasma cortisol by day 18. There were no treatment-associated effects on conceptus survival or size. Nor were there treatment-associated effects on allantoic fluid volume or content. Trophodermal glucocorticoid receptor (GR) mRNA expression decreased by 34% (P < 0.05) in metyrapone-treated pigs, and was not further influenced by concomitant administration of cortisol, thereby suggesting an influence of aldosterone on GR mRNA expression. Also, when all pigs were considered, there were treatment-independent second-order polynomial regressions (P < 0.05) between maternal plasma cortisol concentrations and embryonic weight, allantoic size and allantoic glucose concentrations, and between plasma aldosterone concentrations and trophodermal GR mRNA expression. Such biphasic corticosteroid concentration versus tissue parameter curves are noteworthy, but difficult to interpret validly. They may suggest that an appropriate corticosteroid environment is necessary for optimal porcine embryonic development during this stage of gestation, but cannot overshadow the absence of treatment effects on the porcine embryonic measures evaluated.     

Prior infection of pigs with a genotype 3 swine hepatitis E virus (HEV) protects against subsequent challenges with homologous and heterologous genotypes 3 and 4 human HEV

Hepatitis E virus (HEV) is an important human pathogen. At least four recognized and two putative genotypes of mammalian HEV have been reported: genotypes 1 and 2 are restricted to humans whereas genotypes 3 and 4 are zoonotic. The current experimental vaccines are all based on a single strain of HEV, even though multiple genotypes of HEV are co-circulating in some countries and thus an individual may be exposed to more than one genotype. Genotypes 3 and 4 swine HEV is widespread in pigs and known to infect humans. Therefore, it is important to know if prior infection with a genotype 3 swine HEV will confer protective immunity against subsequent exposure to genotypes 3 and 4 human and swine HEV. In this study, specific-pathogen-free pigs were divided into 4 groups of 6 each. Pigs in the three treatment groups were each inoculated with a genotype 3 swine HEV, and 12 weeks later, challenged with the same genotype 3 swine HEV, a genotype 3 human HEV, and a genotype 4 human HEV, respectively. The control group was inoculated and challenged with PBS buffer. Weekly sera from all pigs were tested for HEV RNA and IgG anti-HEV, and weekly fecal samples were also tested for HEV RNA. The pigs inoculated with swine HEV became infected as evidenced by fecal virus shedding and viremia, and the majority of pigs also developed IgG anti-HEV prior to challenge at 12 weeks post-inoculation. After challenge, viremia was not detected and only two pigs challenged with swine HEV had 1-week fecal virus shedding, suggesting that prior infection with a genotype 3 swine HEV prevented pigs from developing viremia and fecal virus shedding after challenges with homologous and heterologous genotypes 3 and 4 HEV. The results from this study have important implications for future development of an effective HEV vaccine.     

Surplus dietary tryptophan reduces plasma cortisol and noradrenaline concentrations and enhances recovery after social stress in pigs

Social stress occurs in intensive pig farming due to aggressive behavior. This stress may be reduced at elevated dietary levels of tryptophan (TRP). In this study, we compared the effects of high (13.2%) vs. normal (3.4%) dietary TRP to large neutral amino acid (LNAA) ratios on behavior and stress hormones in catheterized pigs ( approximately 50 kg BW), which were exposed to social stress by placing them twice into the territory of a dominant pig ( approximately 60 kg) for 15 min. Pre-stress plasma TRP concentrations were 156+/-15 vs. 53+/-6 micromol/l (p<0.01) in pigs on the high vs. normal TRP diets, respectively. Pre-stress plasma cortisol and noradrenaline concentrations were twofold (p<0.01) and 1.4-fold (p<0.05) lower but plasma adrenaline concentration was similar in pigs on the high vs. normal TRP diets, respectively. During the social confrontations, pigs on the high vs. normal TRP diets show a tendency towards reduced active avoidance behavior (3.2+/-1.1 vs. 6.7+/-1.2 min, p<0.1) but their physical activity (8.5+/-0.6 vs. 10.2+/-0.8 min) and aggressive attitude towards the dominant pig (11+/-3 vs. 7+/-2 times biting) were similar. Immediate (+5 min) post-stress plasma cortisol, noradrenaline and adrenaline responses were similar among dietary groups. After the social confrontations, the post-stress plasma cortisol, noradrenaline and adrenaline concentrations and/or curves (from +5 min to 2 h) were lower/steeper (p<0.05) in pigs on the high vs. normal TRP diets. In summary, surplus TRP in diets for pigs (1) does not significantly affect behavior when exposed to social stress, (2) reduces basal plasma cortisol and noradrenaline concentrations, (3) does not affect the immediate hormonal response to stress, and (4) reduces the long-term hormonal response to stress. In general, pigs receiving high dietary TRP were found to be less affected by stress.     

癫痫发作前后血清皮质醇水平的变化

利用ＲＩＡ法测定经皮层ＥＥＧ、ＰＥＴ、ＳＰＥＣＴ、ＭＲＩ、ＣＴ等检查而定位明确的６４例癫痫患者痫痫发作前后血清皮质醇水平。结果表明,癫痫病人血清基础皮质醇水平明显低于正常人。癫痫发作后９２．２％的病人血清中皮质醇水平升高,４０．６％的病人发作后１５分钟皮质醇水平达到峰值,失神经发作后血清皮质醇水平不增加或增加不明显,而强－阵挛性,复杂部分性发作后皮质醇水平明显升高。然而发作后血清皮质醇水平的变化与     

Diurnal rhythms in plasma cortisol, insulin, glucose, lactate and urea in pigs fed identical meals at 12-hourly intervals

Diurnal rhythms in plasma cortisol, insulin, glucose, lactate and urea concentrations were investigated in eight catheterized pigs of approximately 35 kg BW. Pigs were fed isoenergetic/isoproteinic diets at a restricted level (2.5 x maintenance requirement for energy) in two daily rations (06:00 and 18:00 hours) in order to obtain equal intervals between feed intake. Preprandial plasma cortisol concentration was 22+/-3 ng/mL in the morning and 14+/-2 ng/mL in the evening (p<0.025), whereas the concentrations of insulin, glucose, lactate, and urea were similar. In the postprandial period in the morning (06:00-09:00 hours) plasma cortisol, insulin and lactate concentrations (expressed as the total area under the curve) were greater (p<0.001) compared to the evening (18:00-21:00 hours) by 100%, 42%, and 24%, respectively, while postprandial plasma glucose and urea concentrations were not affected by time of the meal. When postprandial plasma concentrations were expressed as a response over preprandial concentrations (decremental or incremental area under the curve), the diurnal rhythm was not observed for cortisol and glucose, persisted for insulin and lactate, and appeared for urea with a smaller postprandial urea response (p<0.05) in the morning compared to the evening. We conclude that the diurnal rhythm in plasma cortisol is independent of feeding whereas the diurnal rhythms in plasma insulin, lactate and urea are unveiled by the morning/evening meals in pigs. At equal 12-h intervals between meals, the postprandial responses of lactate and urea show diurnal variations, each in a specific manner, which suggest decreased postprandial efficiency of carbohydrate metabolism and increased postprandial efficiency of protein metabolism in the morning compared to the evening.     

Enzyme-linked immunosorbent assay for detection of antibody to Treponema hyodysenteriae antigens.

The enzyme-linked immunosorbent assay (ELISA) was evaluated and compared with the microtitration agglutination test for the detection of swine antibody to Treponema hyodysenteriae lipopolysaccharide antigens. Cells of T. hyodysenteriae serotypes 1 and 2 were extracted with hot phenol-water (68 degrees C). The lipopolysaccharide fraction from the aqueous phase was coated on plastic wells at concentrations of 1 micrograms (serotype 1) and 10 micrograms (serotype 2) of carbohydrate per ml. The ELISA was serotype specific when lipopolysaccharide antigens were reacted against sera from convalescent swine. Seroconversion of infected pigs was detectable with the ELISA within 1 to 2 weeks postinoculation and with the microtitration agglutination test 2 to 3 weeks postinoculation. Antibody titers could be detected in convalescent pigs as long as 19 weeks postinoculation by the ELISA and 12 to 13 weeks postinoculation by the microtitration agglutination test. Therefore, the ELISA may be useful for the detection of asymptomatic carriers.     

Virulence properties and protective efficacy of the capsular polymer of Haemophilus (Actinobacillus) pleuropneumoniae serotype 5.

The role of the capsule of Haemophilus (Actinobacillus) pleuropneumoniae serotype 5 in bacterial virulence, and the protective efficacy of antibody to serotype 5 capsule was investigated. Encapsulated H. pleuropneumoniae serotype 5 were resistant to killing by complement and antibody to capsule or somatic antigens, whereas a noncapsulated mutant was sensitive to killing by the alternative complement pathway alone. Antiserum to whole H. pleuropneumoniae serotype 5 bacteria or monospecific antiserum to capsule was capable of opsonizing bacteria of the homologous serotype for phagocytosis by swine polymorphonuclear leukocytes but was not opsonic for a heterologous serotype. An immunoglobulin M monoclonal antibody to the serotype 5 capsule was not opsonic for any serotype. Mice were protected against lethal, intranasal challenge with the homologous or heterologous serotype after immunization with live encapsulated or noncapsulated bacteria, but not after immunization with killed bacteria, lipopolysaccharide, or a capsule-protein conjugate vaccine. The protection induced by immunization with live bacteria was transferred to nonimmune, syngeneic mice by serum but not by spleen cells. Nonimmune pigs passively immunized with monospecific swine serum to capsule were protected from lethal infection but not from development of hemorrhagic lung lesions, whereas pigs passively immunized with swine antiserum to live bacteria did not develop severe respiratory lesions. Thus, the capsule of H. pleuropneumoniae serotype 5 was inhibitory to the bactericidal activity of serum and was antiphagocytic. Antibody to the capsule was opsonic but was not fully protective.     

Molecular and serological survey of hepatitis E virus infection among domestic pigs in Inner Mongolia, China

To evaluate the prevalence and characteristics of swine hepatitis E virus (HEV) infection in Inner Mongolia, China, serum samples obtained from 356 2- to 4-month-old pigs on 14 farms in Inner Mongolia were tested for the presence of anti-HEV antibodies and HEV RNA. Overall, 186 pigs (52%) tested positive for anti-HEV antibodies, while 30 pigs (8%) had detectable HEV RNA levels. The 30 HEV isolates recovered from the viremic pigs were phylogenetically classified into genotype 4 and differed from each other by up to 15.3% in a 412 nt sequence within ORF2. The Inner Mongolian swine HEV strains were most similar to human or swine HEV strains isolated in the other provinces of China but differed by 15.9–18.9% from those in Mongolia (formerly known as Outer Mongolia). These results indicate that farm pigs in Inner Mongolia are frequently infected with markedly divergent genotype 4 HEV strains that may be indigenous to China.     

Immunization of swine with heat-stable Escherichia coli enterotoxin coupled to a carrier protein does not protect suckling pigs against an Escherichia coli strain that produces heat-stable enterotoxin.

Pregnant swine were immunized parenterally with purified heat-stable Escherichia coli enterotoxin that was made antigenic by coupling it to bovine immunoglobulin G. Immunized swine had high titers of antitoxin in serum and colostrum as measured by radioimmunoassay. However, the heat-stable enterotoxin neutralizing titers of the serum and colostrum from immunized swine were comparatively low. Newborn pigs suckling their immunized dams were not protected against challenge with porcine enterotoxigenic E. coli that produce heat-stable toxin but do not produce heat-labile toxin.     

Lipopolysaccharide-induced increases in porcine serum cortisol and progesterone concentrations are not mediated solely by prostaglandin F2α

The increase in steroid hormone blood levels in response to bacterial lipopolysaccharide (LPS) appears to be an important mechanism by which mammalian species regulate inflammation. This study examined changes in serum concentrations of cortisol, progesterone, and 13,14-dihydro-15-keto-prostaglandin F₂ (PGFM) in diestrous pigs following the intravenous injection of LPS and determined whether indomethacin would attenuate these changes. Serum cortisol and progesterone concentrations increased (P<0.05) within 30 min after the administration of LPS, and the increases in steroid hormones were accompanied by a sharp, transient increase (P<0.05) in PGFM levels. In the presence of indomethacin, serum PGFM levels did not change (P>0.05); however, LPS enhanced (P<0.05) cortisol and progesterone concentrations, although the increases were delayed. Serum concentrations of cortisol acutely increased (P<0.05) immediately following both infusions of indomethacin. In summary, cortisol and progesterone concentrations increased irrespective of serum PGFM concentrations, thereby indicating that prostaglandin F₂ was not the sole mediator of LPS-induced changes in cortisol and progesterone concentrations.     

Effect of stress on basophil function in chronic idiopathic urticaria

Background Chronic idiopathic urticaria (CIU) is a distressing skin condition involving recurrent itchy hives lasting 6 weeks or longer. The mechanism involves mast cell and basophil degranulation, which releases inflammatory mediators including histamine. In our clinical practice, we have observed that the onset of CIU is often preceded by a major life event. Objective To investigate the role of the hormones of the hypothalamic–pituitary–adrenal (HPA) axis in the link between psychological stress and CIU. Methods Thirty people with CIU and 30 normal controls were recruited. A flow cytometric CD63 expression assay was used to quantify basophil activation, and serum cortisol concentrations were measured as an indication of stress. Results Both corticotrophin releasing factor (CRF) and adrenocorticotrophic hormone (ACTH) were shown to activate basophils. There was no significant difference between numbers of CIU patients and normal controls responding to CFR, ACTH or cortisol. However, the responses in the CIU patients were stronger than those in normal controls. There was also a trend towards higher serum cortisol concentrations in CIU patients. The basophil response to CRF and ACTH correlated with the serum cortisol concentration in normal controls, but not in CIU patients. Conclusions Although our data have not supported the hypothesis that stress makes a major contribution to CIU, the heightened basophil response to CFR and ACTH and higher levels of serum cortisol do suggest a derangement of the HPA axis in CIU.     

Change of electrophoretic mobility of purified alternative pathway factor D

The electrophoretic mobility of factor D (D) of the alternative pathway of human complement activation was examined by the method of lysoelectrophoresis. Purified D was found to have beta-mobility, while D in fresh serum showed alpha-mobility. Addition of D-depleted serum to D induced a change of electrophoretic mobility from beta to alpha. Addition of guinea pig serum to D did not produce this change. The change of electrophoretic mobility of D was not due to complex formation between D and other known alternative factors, P, C3NeF, B and C3. The Factor(s), which mediated the change in the electrophoretic mobility of D, had pseudoglobulin properties and was distributed around the third peak on Sephadex G-200 gel filtration of human serum with a mol. wt. of 50,000-80,000. This phenomenon might be restricted to a semi-solid state reaction, because complexes containing D were not observed upon analyses by sucrose density gradient ultracentrifugation and isoelectrofocusing.     

Individual behavioural characteristics in pigs--influences of group composition but no differences in cortisol responses

To determine the effect of group composition on backtest (Bt) responses and to determine the predictive value of the Bt for the physiological stress response to weaning and mixing, 814 pigs were backtested at 3, 10 and 17 days of age. Twenty-nine percent of all pigs were cross-fostered at 3 days according to Bt responses and groups were formed of animals with high responses (HR) only, low responses (LR) only or mixed groups of animals with high, intermediate and low responses (MISC). Original litters (OR, no cross-fostering) were used as controls. Cortisol responses were measured in saliva after weaning at 4 weeks of age and after moving and mixing at 9 weeks of age.In HR groups, mean Bt responses decreased after cross-fostering while in LR groups, mean Bt scores increased. In both groups, Bt responses of individual animals before and after cross-fostering were not correlated. In MISC and OR groups, all Bt scores were correlated. Weaning and mixing caused a significant rise in cortisol in all animals while moving or weighing did not. No relations were found between Bt scores and cortisol levels.We conclude that Bt behaviour can change according to the social environment between 3 and 10 days. This could be intentional, to form a varied group, or it might be caused by a change in the hypothalamic-pituitary-adrenal (HPA) function due to social stress. At an older age, this ability is lost and common farm practises such as regrouping, weaning and mixing of piglets at ages >10 days might have a negative effect on the piglets.     

Immunity in barren and enriched housed pigs differing in baseline cortisol concentration

It was shown in a recent study [De Jong IC, Prelle IT, Van de Burgwal JA, Lambooij E, Korte SM, Blokhuis HJ, Koolhaas JM. Effects of environmental enrichment on behavioral responses to novelty, learning and memory and the circadian rhythm in cortisol in growing pigs. Physiol Behav, in press.] that barren housed pigs (small pens, no substrate) have a blunted circadian rhythm of salivary cortisol as compared to enriched housed pigs (large pens with daily fresh bedding). In the light period, enriched housed pigs showed significantly higher concentrations of cortisol in saliva than barren housed pigs, whereas in the dark period, cortisol concentrations were low in both enriched and barren housed pigs. In the present study, the immunological consequences of the difference in baseline salivary cortisol concentration in the light period were evaluated. It appeared that leukocyte and lymphocyte distributions, and in vitro lymphocyte proliferation following ConcanavalineA (ConA) stimulation in the assay using purified lymphocytes were not affected. However, barren and enriched housed pigs did show a different proliferation response to ConA in the whole blood assay. At day 2 of culture, proliferation was higher in barren housed pigs than in enriched housed pigs, whereas at day 4 of culture, proliferation was higher in enriched housed pigs than in barren housed pigs. Lymphocyte proliferation at day 2 of culture in the whole blood assay correlated negatively with plasma cortisol levels, which might thus explain the higher proliferation in barren housed pigs at day 2 of culture. The in vivo humoral and cellular (delayed type hypersensitivity, DTH) immune response to KLH was not affected by housing conditions. We conclude that, although baseline salivary cortisol concentrations differ between enriched and barren housed pigs, immune function appears to be relatively unaffected.     

Comparison of immune responses against foot-and-mouth disease virus induced by fusion proteins using the swine IgG heavy chain constant region or beta-galactosidase as a carrier of immunogenic epitopes

Previously, we demonstrated that a fusion protein (Gal-FMDV) consisting of beta-galactosidase and an immunogenic peptide, amino acids (141-160)-(21-40)-(141-160), of foot-and-mouth disease virus (FMDV) VP1 protein induced protective immune responses in guinea pigs and swine. We now designed a new potential recombinant protein vaccine against FMDV in swine. The immunogenic peptide, amino acids (141-160)-(21-40)-(141-160) from the VP1 protein of serotype O FMDV, was fused to the carboxy terminus of a swine immunoglobulin G single heavy chain constant region and expressed in Escherichia coli. The expressed fusion protein (IgG-FMDV) was purified and emulsified with oil adjuvant. Vaccination twice at an interval of 3 weeks with the emulsified IgG-FMDV fusion protein induced an FMDV-specific spleen proliferative T-cell response in guinea pigs and elicited high levels of neutralizing antibody in guinea pigs and swine. All of the immunized animals were efficiently protected against FMDV challenge. There was no significant difference between IgG-FMDV and Gal-FMDV in eliciting immunity after vaccination twice in swine. However, when evaluating the efficacy of a single inoculation of the fusion proteins, we found that IgG-FMDV could elicit a protective immune response in swine, while Gal-FMDV only elicited a weak neutralizing activity and could not protect the swine against FMDV challenge. Our results suggest that the IgG-FMDV fusion protein is a promising vaccine candidate for FMD in swine.