Per Wallgren

The effect of zinc oxide supplementation on the stability of the intestinal flora with special reference to composition of coliforms in weaned pigs

The effect of a dietary supplementation of zinc oxide (ZnO) on the stability of the intestinal flora and on the composition of coliforms in weaned pigs was investigated. Faecal floras were characterized by their metabolic activities and fermentative capacity (FC) using the Phene Plate generalized microplate. Coliforms were characterized by conventional enumeration and by the Phene Plate‐RS plates. The latter measured FC, phenotypic diversity, persistence of each coliform strain in piglets, and similarity among the coliform populations within groups. From weaning onwards, the control pigs (n = 5) were fed a basal diet ad libitum, while experimental pigs (n = 5) were given the same food supplemented with 2500 ppm ZnO. Metabolic fingerprinting of faecal floras indicated marked differences between the composition of floras of treated and control pigs during the first 2 weeks post‐weaning. The FC of faecal flora in both groups decreased as pigs aged, but it was significantly (P≤ 0·0001) lower in control pigs during the first 2 weeks post‐weaning. Neither the number of coliforms, nor their FC‐values, differed between the groups. However, during the first 2 weeks post‐weaning, there was a significant increase in both variety (P = 0·019) and diversity (P≤ 0·001) of coliforms in control pigs compared with the ZnO treated group. Homogeneity between coliform populations of piglets was high during the suckling period, indicating the presence of many identical strains among piglets. This, however, decreased in control pigs during the first 2 weeks post‐weaning. Several coliform strains that colonized the gut at the early stage of the pigs’ life were found to be resident in animals of both groups. It is concluded that supplementation of ZnO to weaned pigs helped to maintain the stability of the intestinal microflora and the diversity of coliforms during the first 2 weeks post‐weaning, but not later, and that ZnO supplementation to creep feed should be restricted to the first 2 weeks post‐weaning in veterinary practice.

Detection of a novel porcine boca-like virus in the background of porcine circovirus type 2 induced postweaning multisystemic wasting syndrome.

Porcine circovirus type 2 (PCV-2) has been found to be the causative agent of postweaning multisystemic wasting syndrome (PMWS). However, PCV-2 is a ubiquitous virus in the swine population and a majority of pigs infected with PCV-2 do not develop the disease. Different factors such as age, maintenance, the genetics of PCV-2, other pathogens, etc. have been suggested to contribute to the development of PMWS. However, so far no proven connection between any of these factors and the disease development has been found. In this study we explored the possible presence of other so far unknown DNA containing infectious agents in lymph nodes collected from Swedish pigs with confirmed PMWS through random amplification and high-throughput sequencing. Although the vast majority of the amplified genetic sequences belonged to PCV-2, we also found genome sequences of Torque Teno virus (TTV) and of a novel parvovirus. The detection of TTV was expected since like PCV-2, TTV has been found to have high prevalence in pigs around the world. We were able to amplify a longer region of the parvovirus genome, consisting of the entire NP1 and partial VP1/2. By comparative analysis of the nucleotide sequences and phylogenetic studies we propose that this is a novel porcine parvovirus, with genetic relationship to bocaviruses.

Dietary zinc oxide in weaned pigs — effects on performance, tissue concentrations, morphology, neutrophil functions and faecal microflora

The uptake and distribution of zinc in tissues and the effects of 2500 ppm dietary zinc oxide on health, faecal microflora, and the functions of circulating neutrophils were evaluated in weaned pigs. One group was fed a zinc supplement diet and another group was used as a control. All pigs remained healthy throughout the study, but the supplemented animals showed better performance than the controls. The serum zinc values rose rapidly. At autopsy, carried out at the age of 63 days, the zinc concentrations in liver tissue were 4.5 times higher, and in renal tissue two times higher in the supplemented group than in controls (P<0.001). Microscopic examination showed increased lipid accumulation in hepatocytes from supplemented pigs. No effect on the number of excreted Escherichia coli and enterococci per gram faeces or on the functions of circulating neutrophils was observed. Dietary supplementation with 2500 ppm ZnO for up to two weeks after weaning appears to be potentially beneficial in the prevention of postweaning diarrhoea in pigs.

Studies of porcine circovirus type 2, porcine boca-like virus and torque teno virus indicate the presence of multiple viral infections in postweaning multisystemic wasting syndrome pigs.

In a previous study, using random amplification and large-scale sequencing technology, we identified a novel porcine parvovirus belonging to the genus Bocavirus in the background of porcine circovirus type 2 (PCV-2) in Swedish pigs with postweaning multisystemic wasting syndrome (PMWS). In addition to bocavirus we demonstrated the presence of torque teno virus (TTV) genogroups 1 and 2 in these cases of PMWS, indicating the simultaneous presence of several viruses in this disease complex. In the present study, 34 PMWS-affected animals and 24 pigs without PMWS were screened by PCR for the presence of PCV-2, TTV-1, TTV-2 and porcine boca-like virus (Pbo-likeV). The studies revealed the following infection rates in the PMWS-affected pigs: PCV-2 100%, TTV-1 77%, TTV-2 94% and Pbo-likeV 88%. In comparison, the pigs without PMWS had the following rates: PCV-2 80%, TTV-1 79%, TTV-2 83% and Pbo-likeV 46%. The sequence identity between the different Swedish Pbo-likeV sequences ranged between 98% and 100%. By checking co-infection, it was found that 71% of the PMWS-affected pigs harbor simultaneously all these viruses. As a contrast, in the group without PMWS only 33% of the animals were positive simultaneously for these viruses. These observations indicate a multiple viral infection in PMWS-affected pigs. It has to be studied further if the clinical manifestation of PMWS might be due to synergistic effects of different viruses acting together.

Experimental reproduction of postweaning multisystemic wasting syndrome (PMWS) in pigs in Sweden and Denmark with a Swedish isolate of porcine circovirus type 2

Abstract An experimental model using 3-day-old snatch-farrowed colostrum-deprived piglets co-infected with porcine circovirus type 2 (PCV2) and porcine parvovirus (PPV) is at present one of the best methods to study factors affecting development of postweaning multisystemic wasting syndrome (PMWS). A Swedish isolate of PCV2 (S-PCV2) retrieved in 1993 from a healthy pig has been used in this model to reproduce PMWS in pigs from Northern Ireland. This virus has been present in the Swedish pig population for at least a decade without causing any known PMWS disease problems, despite its potential pathogenicity. The reasons for this are unknown, but could be related to genetics, absence of triggers for PCV2 upregulation (infectious agent and/or management forms) within Swedish pig husbandry. In order to confirm the pathogenicity of S-PCV2, Swedish and Danish pigs were experimentally infected with this isolate according to the established model. Swedish pigs were also infected with a reference isolate of PCV2 (PCV2-1010) to compare the severity of disease caused by the two isolates in Swedish pigs. Both Danish and Swedish pigs developed PMWS after the experimental infection with S-PCV2. Antibodies to PCV2 developed later and reached lower levels in serum from pigs infected with S-PCV2 than in pigs inoculated with PCV2-1010. In general, pigs infected with S-PCV2 showed more severe clinical signs of disease than pigs infected with PCV2-1010, but pigs from all PCV2-inoculated groups displayed gross and histological lesions consistent with PMWS. All pigs inoculated with PPV, alone or in combination with PCV2, displayed interleukin-10 responses in serum while only pigs infected with PPV in combination with PCV2 showed interferon-α in serum on repeated occasions. Thus, the pathogenicity of S-PCV2 was confirmed and a role for cytokines in the etiology of PMWS was indicated.

Reproduction of postweaning multisystemic wasting syndrome in pigs experimentally inoculated with a Swedish porcine circovirus 2 isolate

In recent years, porcine circovirus type 2 (PCV2)—associated postweaning multisystemic wasting syndrome (PMWS) has been reported worldwide. However, to date, PMWS has not been reported in Sweden despite the demonstration of serum antibodies to a PCV2-like virus in Swedish pigs. This communication reports the experimental reproduction of clinical PMWS after inoculation of colostrum-deprived (CD) pigs, derived from a Northern Ireland herd, with an isolate of PCV2 virus recovered from a clinically normal Swedish pig that was necropsied in 1993. The clinical disease and histological lesions observed in CD pigs inoculated with this virus were indistinguishable from those observed in previous studies on CD pigs inoculated with a PCV2 virus isolate recovered from pigs with PMWS. These results highlight the disease potential of PCV2 isolated from regions apparently free of PMWS and suggest that the status of the host and its environment is an important factor in the development of clinical PMWS.

Appearance of interferon-α in serum and signs of reduced immune function in pigs after transport and installation in a fattening farm

Pigs were transported from several breeding facilities at the age of 10-12 weeks and regrouped in a fattening farm, specialized in breeding pigs for subsequent slaughter. Blood samples were obtained from the animals just before transport and daily for 17 days after installation in the fattening farm. On each occasion a group of ten animals (170 animals in total) was sampled. The levels of interferon-alpha (IFN-alpha) in serum were measured as antiviral activity in a cytopathic effect inhibition assay. Beginning at day 4 after installation, a significant proportion of sera contained IFN-alpha, with the highest incidence of IFN-alpha positive animals (25%) and IFN-alpha titers on days 5-10. This indicates a high frequency of viral infections in the animals. The in vitro ability of peripheral blood mononuclear leukocytes (PBMCs) to produce IFN-alpha after stimulation by glutaraldehyde-fixed pseudorabies virus-infected PK15 cells and their proliferative response to the T-cell mitogen leukoagglutinin (LA) was also monitored. There was a significant, but moderate decrease in the ability of PBMCs to produce IFN-alpha during the observation period. In contrast, the response to the mitogen LA decreased markedly during the first 5 days, and thereafter remained at the same low level. The proliferative response to LA was significantly lower for PBMCs from serum of IFN-alpha-positive than from IFN-alpha-negative animals. These impaired PBMC responses could indicate a stress-induced immune depression, possibly contributing to the high incidence of viral infections.

Interleukin 6, serum amyloid A and haptoglobin as markers of treatment efficacy in pigs experimentally infected with Actinobacillus pleuropneumoniae

The possibility to use acute phase proteins to monitor the elimination of a bacterial infection in pigs would facilitate an objective assessment of treatment with various antimicrobial substances. To examine this possibility, the acute phase response (IL-6, serum amyloid A (SAA), and haptoglobin) elicited by Actinobacillus pleuropneumoniae and its reduction on treatment with various antibiotics was studied in serum from specific pathogen free (SPF) pigs. Pigs were infected intranasally with A. pleuropneumoniae serotype 2, and either left as non-treated control pigs or treated with different antibiotics intramuscularly at onset of respiratory disease (20h post-infection). Pigs responded to the infection with prominent increases in activity and concentrations of IL-6, SAA, and haptoglobin. These responses were to a certain extent overlapping and covered the time span from a few hours after infection until development of detectable levels of specific antibodies (7-10 days post-infection in untreated pigs). The haptoglobin response lasted until the end of the study on day 17 and thereby partly coincided with the antibody response. Treatment with antimicrobials that effectively reduced establishment of the infection with A. pleuropneumoniae also reduced the duration of all three acute phase responses, and reduced the concentration of serum haptoglobin. In contrast, less efficacious treatments did not reduce these acute phase responses. Thus, acute phase reactants can be applied to monitor therapeutic effects of antimicrobial drugs in the pig and measurements of IL-6, SAA and haptoglobin could add valuable information about the stage of infection during a disease outbreak.

Influence of experimentally induced endogenous production of cortisol on the immune capacity in swine.

Abstract Field studies have suggested that ‘stressors’, such as transportation and mixing, might interfere with the immune competence of pigs. Therefore, an experimental model was established to study the influence of elevated concentrations of circulating cortisol on the immune capacity in swine. Three experimental groups, with six pigs in each, were immunized twice, 4 weeks apart, with Mycoplasma hyopneumoniae antigen. Endogenous production of cortisol was induced by intramuscular injection of adrenocorticotropic hormone (ACTH) twice daily. One group received ACTH during the week before and after the second immunization, one group during the week after the second immunization only, while one group served as untreated controls. The treatment with ACTH induced high, but physiological, concentrations of cortisol in plasma. Simultaneously, the number of lymphocytes per milliliter blood decreased while the neutrophil number increased. The elevated concentrations of cortisol also coincided with reduced proliferation and interleukin-2 production by blood lymphocytes stimulated with the mitogens concanavalin A and phytohemagglutinin in vitro, while the responses to pokeweed mitogen were less affected. The suppression of mitogen responses was more pronounced in cultures of whole blood than in cultures of purified peripheral blood mononuclear cells (PBMC). Antibody production, induced by M. hyopneumoniae in cultures of purified PBMC was also inhibited by ACTH treatment. Both the rate of increase and the magnitude of the antibody production induced by the primary immunization were reduced. In contrast, no effects of ACTH treatment were recorded for the response to the second immunization or on the serum levels of antibodies to M. hyopneumoniae. The ability of blood leukocytes to produce interferon-α (IFN-α) at exposure in vitro to fixed pseudorabies virus adsorbed to porcine kidney cells increased in all animals shortly after the second immunization with M. hyopneumoniae. The influence of cortisol on the IFN-α-producing capacity was dependent on whether the test was carried out in whole blood cultures or in cultures with purified PBMC. This finding further emphasizes that the relevance of in vitro assays for measuring in vivo phenomena must be carefully scrutinized.

Serodiagnosis of sarcoptic mange in pigs

A serodiagnostic test (ELISA) for detecting antibodies to Sarcoptes scabiei in the sera of pigs was evaluated. The ELISA results from 221 specific pathogen-free pigs of three different age categories were used to establish a cut-off value for the assay. Background optical density values differed significantly between the three groups, the sows having the highest values. The mean + 3 sd of their values was chosen as the cut-off. Four farrow-to-finish herds of pigs with sarcoptic mange were investigated. Skin scrapings were taken from each animal for the demonstration of S scabiei and their sera were assayed for the presence of antibodies to the mite. All the herds had active infections with S scabiei and antibodies to S scabiei were found in a significant number of the animals sampled. The sensitivity and specificity of the ELISA were 87.8 and 99.5 per cent, respectively, employing clinical diagnosis as the gold standard. A higher sensitivity (100 per cent), but a lower specificity (32.8 per cent) was obtained when the results of skin scrapings were used as the gold standard.