Isolation and characterization of porcine circovirus type 2 from pigs showing signs of post‐weaning multisystemic wasting syndrome in the Netherlands

Summary

Pigs with wasting syndrome were examined for macroscopic and histopathological lesions, and for porcine circovirus (PCV). Histopathological lesions were comparable to those previously documented for post‐weaning multisystemic wasting syndrome (PMWS). In addition, in seven out of ten examined PMWS‐affected pigs focal‐to‐slight mononuclear meningitis and focal cerebral mononuclear infiltrates (4 out of 10) were observed. A virus was isolated from organs and sera from pigs showing wasting syndrome. An immunoperoxidase monolayer assay and an indirect immunofluorescence assay were performed on the infected PK‐15 and Dulac cell cultures, respectively, and both assays indicated the presence of PCV type 2 (PCV2). The nested‐polymerase chain reaction (nPCR) technique, based on the use of PCV2 specific oligonucleotides, revealed specific amplified products of 481 bp. Nucleotide sequence analysis of the entire genome of the Dutch PCV isolate 24657 NL showed a homology with known nucleotide sequences of porcine PCV type 1 (PCV1) and PCV2 isolates of 77.1% and >96%, respectively. This is the first report of the isolation and characterization of PCV2 in PMWS‐affected pigs in the Netherlands.     

Oral transmission of porcine reproductive and respiratory syndrome virus by muscle of experimentally infected pigs

The current study was performed to determine if porcine reproductive and respiratory syndrome virus (PRRSV) could be transmitted to pigs by feeding muscle tissue obtained from recently infected pigs. Muscle obtained from pigs infected with either a European strain (EU donor pigs) or American strain (US donor pigs) of PRRSV was fed to PRRSV-free receiver pigs. The donor pigs were slaughtered 11 days post-infection (dpi). PRRSV was detected by conventional virus isolation in muscle at 11 dpi from 7 of 12 EU donor pigs and 5 of 12 US donor pigs. In contrast to conventional virus isolation, all muscle samples from infected pigs were positive for viral nucleic acid by PCR, except for muscle from one animal infected with the American strain of PRRSV. Five hundred grams of raw semimembranosus muscle from each of the donor pigs was fed over a 2 days period (250 g per day) to each of two receiver pigs (48 receiver pigs). The receiver pigs were housed separately in five groups. One of the five groups was fed muscle obtained from US donor pigs that was also spiked with the American strain of PRRSV. Sentinel pigs were placed in-contact with the group of receiver pigs fed spiked muscle. All receiver pigs became viraemic by 6 days post-feeding (dpf). There was evidence of horizontal transmission with sentinel pigs, in-contact with receiver pigs, becoming viraemic. The study demonstrates that PRRSV could be infectious through the oral route via the feeding of meat obtained from recently infected pigs.     

Stochastic simulation of dairy cattle nucleus breeding schemes: Influence of breeding strategy and biased breeding values in the population

SUMMARY: A stochastic simulation model of an open nucleus scheme was used to study the consequences of the breeding strategy and biased lactation records for population cows. Selection was for a single sex-limited trait with a heritability of 0.25 and based on animal model breeding value estimates. Selection of dams was across age classes while sires were required to have a progeny test before they could be selected as proven bull or bull sire. Dams to breed nucleus replacements and young bulls could be selected from the nucleus and the top population which contained 240 and 1600 replacement heifers annually. The first 15 years of the simulated period was used to reach a population with an equilibrium genetic progress for a progeny testing scheme. Comparisons were based on the 25 year period after an alternative breeding scheme was adopted. The annual genetic gain was calculated from the last 10 years of that period. The annual genetic gain in an open nucleus breeding scheme was .247 σ(a) . The annual genetic gain increased 5.4% when MOET was also used on cows selected to breed replacements for the top population. When, in addition the number of sires used on top population cows was reduced from 8 to 4, that being the number used in the nucleus, the annual genetic gain increased by another 2.8%. The reduction in annual genetic gain due to biased lactation records of top population cows ranged from 4.6 to 15.4%. The average bias in estimated breeding values of the top population dams selected to breed nucleus replacements ranged from 0.53 to 2,52 σ(a) . The regression coefficient of the EBV of the bull after progeny testing on the EBV of the dam at the time of selection was 0.55 without biased lactations and ranged from 0.10 to 0.27 with biased lactations. The reduction in genetic gain was especially related to the regression coefficient and to a lesser extent to the average bias. In practice, the expected reduction in annual genetic gain from biased lactation records of population cows is expected to be between 5 and 10 %. ZUSAMMENFASSUNG: Stochastische Simulation von Milchvieh-Nukleussystemen: Einflu? der Zuchtstrategie und verzerrter Zuchtwerte in der Population Eine stochastische Simulation eines offenen Nukleussystems wurde zur Untersuchung der Konsequenzen der Zuchtstrategie und verzerrter Laktationsabschlüsse für Populationskühe untersucht. Selektion bezog sich auf ein einzelnes weibliches Merkmal mit Heritabilit?t von 1/4 und gründete auf Tiermodell Zuchtwertsch?tzungen, Selektion von Muttertieren über Altersklassen, w?hrend Stiere vor der Selektion einen Nachkommenschaftstest haben mu?ten. Muttertiere für Nukleus- und Jungstiere kommen vom Nukleus und Spitzen der Population, die 240 und 1600 nachgestellte Kalbinnen umfa?ten. Die ersten 15 Jahre der simulierten Periode wurden zum Erreichen einer Population mit Gleichgewichtsfortschritt für ein Nachkommenschaftsprüfsystem verwendet. Vergleiche beruhten auf einer 25-Jahre-Periode nach Einrichtung des alternativen Zuchtsystems, und der j?hrliche Zuchtfortschritt wurde für die letzten 10 Jahre berechnet. Der j?hrliche Zuchtfortschritt im offenen Nukleussystem war 0,247 σ(a) und nahm um 5,4% zu, wenn MOETauch für Kühe zum Ersatz der Spitzenpopulation verwendet wurde. Wenn darüber hinaus die Zahl der Vatertiere in der Spitzenpopulation von 8 auf 4 reduziert wurde, die Zahl der im Nukleus verwendeten, konnte der j?hrliche genetische Fortschritt um weitere 2, 8% gesteigert werden. Die Verminderung des Zuchtfortschrittes auf Grund von verzerrten Laktationsabschlüssen der Spitzenkühe der Population variierte von 4,6 bis 15,4%. Die durchschnittliche Verzerrung der gesch?tzten Zuchtwerte der Populationsspitzenkühe für die Nukleusremonte bewegte sich von 0,53 bis 2,52 σ(a) . Der Regressionskoeffizient von EBV der Stiere auf Grund von Nachkommenschaftsprüfung auf EBV der Muttertiere beim Zeitpunkt der Selektion war 0,55 ohne verzerrte Laktationen und schwankte zwischen 0,10 und 0,27 bei verzerrten Laktationen. Die Verminderung des genetischen Fortschritts hing deutlich mit dem Regressionskoeffizient zusammen und weniger mit der durchschnittlichen Verzerrung. In der Praxis ist zu erwarten, da? die Reduktion des Zuchtfortschrittes durch verzerrte Laktationsabschlüsse der Population zwischen 5 und 10% liegt.     

Duration of estrus in relation to reproduction results in pigs on commercial farms.

This research was conducted to determine factors that influence duration of estrus, AI strategy, and reproduction results between and within commercial swine farms that use AI. Data from 15,186 sows and gilts on 55 farms for a period of 6.1+/-4.2 mo per farm were used in this study. The average duration of estrus was 48.4+/-1.0 h, ranging from 31 to 64 h, and was consistent from month to month within a farm (repeatability of 86%). Differences in duration of estrus between farms accounted for 23% of the total variation in duration of estrus. On most farms (n = 45), gilts showed a shorter (P < .05) duration of estrus than sows (40.8+/-1.1 h vs 48.5+/-1.0 h). The duration of first estrus after weaning was longer (P < .0001) compared with that of repeat-breeder sows (50.2+/-1.0 h vs 46.8+/-1.0 h). Duration of estrus decreased (P < .05) when interval from weaning to estrus increased from 4 to 6 d (56.0 +/- 1.2 h vs 45.8 +/-1.2 h). The regression of interval from onset to estrus to first AI and interval from weaning to estrus varied between farms and ranged from -7.4 to +1.3 h/d; four farms had a positive relationship. Farrowing rate decreased (P < .05) from 89.7+/-2.7% to 78.2+/-5.74 when the interval from weaning to estrus increased from 4 to 10 d. The litter size decreased (P < .05) from 11.7 to 10.6 pigs when the interval from weaning to estrus increased from 4 to 7 d. Compared with a single AI, double AI in sows and gilts resulted in a 4.3 and 7.0% higher (P < .05) farrowing rate, respectively. When the first AI was performed after expected ovulation, reproduction results were lower than when AI was performed before or at expected ovulation in sows. Duration of estrus was not related to farrowing rate or litter size in individual pigs. Number of inseminations per estrus, time of AI, and duration of estrus were correlated, which made it difficult to assess which of these factors was primarily related to the farrowing rate or litter size. Knowledge of average duration of estrus on farms and of factors that influence the duration of estrus on commercial farms can help to improve the efficiency of the AI strategy specific for each farm.     

Isolation and characterization of porcine circovirus type 2 from pigs showing signs of post-weaning multisystemic wasting syndrome in The Netherlands

Pigs with wasting syndrome were examined for macroscopic and histopathological lesions, and for porcine circovirus (PCV). Histopathological lesions were comparable to those previously documented for post-weaning multisystemic wasting syndrome (PMWS). In addition, in seven out of ten examined PMWS-affected pigs focal-to-slight mononuclear meningitis and focal cerebral mononuclear infiltrates (4 out of 10) were observed. A virus was isolated from organs and sera from pigs showing wasting syndrome. An immunoperoxidase monolayer assay and an indirect immunofluorescence assay were performed on the infected PK-15 and Dulac cell cultures, respectively, and both assays indicated the presence of PCV type 2 (PCV2). The nested-polymerase chain reaction (nPCR) technique, based on the use of PCV2 specific oligonucleotides, revealed specific amplified products of 481 bp. Nucleotide sequence analysis of the entire genome of the Dutch PCV isolate 24657 NL showed a homology with known nucleotide sequences of porcine PCV type 1 (PCV1) and PCV2 isolates of 77.1% and >96%, respectively. This is the first report of the isolation and characterization of PCV2 in PMWS-affected pigs in the Netherlands.     

Sequence analysis of the membrane protein gene and nucleocapsid gene of porcine reproductive and respiratory syndrome virus isolated from a swine herd in Hungary

Porcine reproductive and respiratory syndrome virus (PRRSV) was isolated from blood samples taken at a pig farm in Hungary from pigs showing clinical signs of the disease. The virus (ABV 32) was identified as belonging to the European genotype by using type-specific monoclonal antibodies. This was confirmed by comparing the sequence of the membrane protein gene (ORF 6) and the nucleocapsid gene (ORF 7) with the American VR2332 and the European LV genotype reference strain, respectively. Analysis of the amino acid sequence of the ORF 6 and ORF 7 of ABV 32 revealed five amino acid changes in both ORFs when compared with LV, of which two changes in ORF 7 were only found in the Spanish isolates. Additionally, the ORF 7 sequence was compared with corresponding sequences of a total of 21 other European strains. Phylogenetic analysis using the PHYLIP package confirmed the close relationship between the Hungarian and the Spanish isolates. Of all the isolates analysed, ABV 32 and LV were the least related.