A cohort study about clinical post-weaning multisystemic wasting syndrome (PMWS) in pigs of different genetic background

1. A.I. Pietrain n=30 / batch 7 weeks 13 weeks 16 weeks 21 weeks Pregnancy weaning Slaughter house A.I. Current breed + individual weight + clinic n=30 / batch Figure 1: cohort study protocol within each farm Cox Proportional hazards regression model Hazard ratio C. I. (95%) 0.2-0.4 - 1.3-2.5 - 1.5-4.0 - 1.6-4.2 - PCV-2 status of the dams after farrowing Positive Negative PCV-2 status of the growing pigs (13 weeks-old) Positive Negative Parvovirus status of the dams (>1 month gestation) Titre10240 (highly positive) Titre <10240 Injuries as results of injections (dams’ neck) Presence Absence 0.2 1.0 1.8 1.0 2.4 1.0 2.6 1.0 • A cohort study about clinical post-weaning multisystemic wasting syndrome (PMWS) in pigs of different genetic background • Rose N., Chauvin, C., Abhervé-Guéguen A., Le Diguerher G., Eveno E., • Jolly J.P., Blanchard P., Oger, A., Jestin A., Madec F. French Agency for Food Safety, Zoopole, Ploufragan, B.P. 53, France, F22440 AIM We tested the effect of the implementation of the Pietrain breed in the boar on the occurrence of clinical PMWS in the offspring MATERIAL AND METHODS A cohort study was carried out in four farrow-to-finish commercial farms affected by the syndrome (the diagnosis at the farm level included necropsy and histology on clinically affected pigs and a significant increase in mortality due to PMWS). The study started before the insemination of sows with a random selection of the dams receiving Pietrain semen and those inseminated with semen from boars of the current breed in use on the farm. At birth, 30 pigs per genetic background were randomly selected and individually identified. Those piglets were followed from birth to slaughter (figure 1). Two successive batches were followed per farm. Statistical analysis was carried out using survival analysis (proc PHREG, SAS) taking into account correlation within farms through the robust sandwich estimate for the covariance matrix(1). The outcome was the time to event status which was defined as a change from a healthy to a clinically PMWS-affected status. A multivariable Cox proportional hazards model was built for selected variables (p<0.25) meeting the proportional-hazards assumption (2) using a stepwise-procedure elimination. RESULTS AND DISCUSSION The genetic background of the pigs was not significantly related to the time to PMWS clinic (p=0.48). When growing pigs tested positive for PCV-2 (13 weeks-old) and when their dams were negative after farrowing, the risk of clinical PMWS was increased. The risk was also increased when piglets were born from sows with high Parvovirus titre during gestation and exhibiting neck injuries as results of non properly performed injections (table 1). The quality of the vaccination against the Parvovirus might be of a great importance in this context. Table 1. Variables and variable categories in the final model for time to clinical PMWS. (n=279 followed pigs, 4 farrow-to-finish farms, France, 2002). REFERENCES 1 Lin D.Y., Wei L.J., 1989. The robust inference for the Cox Proportional Hazards Model, Journal of the American Statistical Association 84: 1074-1078. 2 Schoenfeld D., 1982. Partial residuals for the proportional hazards regression model, Biometrika 69: 239-241.