Study Design

In total, eight sows and their offspring were used in this study. The multiparous sows were purchased in late pregnancy from a commercial breeding farm with a high veterinary hygiene standard (Bundes Hybrid Zucht Programm, BHZP, Dahlenburg-Ellringen, Germany). They were transported to the high containment facilities at the Friedrich-Loeffler-Institute Greifswald, Insel Riems, Germany, five weeks before farrowing. According to EU legislation, the animals were kept in open pens in sets of two before they were moved to commercial farrowing pens one week before farrowing. Two farrowing pens were integrated in one stable room so that each experimental group could be kept together. All animals had access to water ad libitum and were fed with commercial feed for breeding sows and after farrowing for lactating sows. All applicable animal welfare regulations, including EU-Directive 2010/63/EC and institutional guidelines, were taken into consideration. The animal experiment was approved by the competent authority, Landesamt für Landwirtschaft, Lebensmittelsicherheit und Fischerei Mecklenburg-Vorpommern (LALLF MV), under reference number LALLF 7221.3-1-059/16.

All animals were tested prior to arrival with negative PCR-results for PEDV and antibodies against PEDV. After arrival, the animals were randomly assigned to four treatment groups. Two sows (ear tags 1871 and 4249) were orally inoculated with cell culture adapted PEDV (PEDV EU) four weeks before farrowing to induce MDA-positive piglets (group A1). Another two sows (ear tags 4423 and 6150) were treated the same way orally with German field material (organ suspension and fecal homogenate; DE) containing PEDV to also obtain MDA-positive piglets (group B1). The remaining four sows stayed untreated to obtain MDA-negative piglets (group A2: ear tags 4343 and 4454; group B2: ear tags 1866 and 4365).

All piglets born alive were individually ear tagged prior to challenge inoculation. Piglets born to sows of groups A1 (9 piglets of sow 4249 and 12 piglets of sow 1871) and A2 (7 piglets of sow 4454 and 7 piglets of sow 4343) were orally challenged with PEDV EU at an age of three to six days whereas piglets born to sows of groups B1 (7 piglets of sow 6150 and 5 piglets of sow 4423) and B2 (8 piglets of sow 4365 and 8 piglets of sow 1866) received the German field material (DE).

During the whole trial, daily rectal swabs (COPAN plain cotton swabs without medium) were taken of all animals for real-time reverse transcription polymerase chain reaction (RT-qPCR) analyses. Samples of days 0 to 7 post inoculation (pi) as well as days 10 pi and 13 pi were tested. Moreover, samples were tested from day 21 pi till the end of the trial.

Additional rectal swabs were taken of four randomly chosen piglets of each sow prior to inoculation and two days afterwards for bacteriological examination. Moreover, clinical signs indicative for PED were recorded using a standardized score system (see Table 2). Blood samples were taken at the day of inoculation and the day of slaughter or euthanasia. Additional blood and colostrum samples were collected from all sows during farrowing. Furthermore, milk samples were collected from all but two sows at the day of slaughter (samples missing from sow 4249 which died from septicemia, and sow 1871 which milk production had already ceased). At the end of the trial, all remaining piglets were euthanized and seven sows were slaughtered (electro-stunning and subsequent exsanguination). All animals were necropsied and samples of the small intestine were taken.