Prevention of the spread of porcine reproductive and respiratory syndrome virus in endemically infected pig herds by nursery depopulation

Abstract

An attempt was made to prevent the spread of the virus of porcine reproductive and respiratory syndrome (PRRS) on three Minnesota pig farms that had been experiencing chronic nursing pig problems, including poor growth rates and increased mortality of post weaning pigs. The PRRS virus and different bacterial pathogens were isolated from all three farms during the initial investigation, and all the farms had a high prevalence of PRRS virus-seronegative breeding animals. All the pigs tested within one week after weaning when they were 18 to 22 days old, were seronegative, whereas 80 to 100 per cent of the pigs tested at eight to nine weeks had antibody titres ranging from 1:64 to 1:1024 by an indirect fluorescent antibody method. The seroprevalence among the finishing pigs on the three farms ranged from 25 to 50 per cent. An eradication protocol was established on each farm, involving emptying the nurseries, followed by pumping out the slurry pits and cleaning, washing and disinfecting three times in 14 days. After the nurseries were repopulated there were improvements in nursery mortality and average daily weight gain, and no seropositive animals were detected in the nurseries on any of the farms; the seronegative status was maintained for the six-month testing period.

A review of evidence for immunosuppression due to Porcine Reproductive and Respiratory Syndrome Virus

“…Circumstantial evidence for an interaction between PRRSV and other disease agents is borne out by the observation that the elimination of PRRSV on farms, by nursery depopulation, resulted in improved growth with decreased isolation and association of disease with secondary pathogens [23,24]. It could be argued, however, that such husbandry control methods, designed to eliminate PRRSV, would also reduce the transmission of these other pathogens.…”

Evaluation of Enzyme-Linked Immunosorbent Assay (ELISA)and Immunofluorescent Antibody (IFA) Test for the Detection of Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) Antibody in Pigs from Conventional Farms.

“…It was recommended to segregate non-infected weaning group from the elder infected group to prevent the spread of PRRSV. Nursery depopulation and multiple site production system were designed for this purpose [10]. However, the varying onset time of infection makes a PRRSV control programs of the segregated production system very difficult.…”

Evaluation of the effects of nursery depopulation on the persistence of porcine reproductive and respiratory syndrome virus and the productivity of 34 farms

“…Before the study began, 10 blood samples were taken from eight-to 10-week-old nursery pigs, serum was collected by centrifugation and sent to the University of Minnesota swine virology laboratory for IFA analysis. The protocol for nursery depopulation previously described involved housing the depopulated pigs in facilities on a different site (Dee and Joo 1994). Nurseries were also allowed to remain empty for 14 days after they were depopulated (downtime).…”