Herd factors associated with the seroprevalences of four major respiratory pathogens in slaughter pigs from farrow-to-finish pig herds Dominiek Maes, Hubert Deluyker, Marc Verdonck, Frans Castryck, Cora Miry, Bernard Vrijens and Aart de Kruif Vet. Res., 31 3 (2000) 313-327 DOI: 10.1051/vetres:2000122