Abstract
Herd differences in disease incidence in 70 Norwegian pig herds were assessed by health card registrations. Such differences proved to be considerable. The incidence of the MMA-syndrome, mastitis, metritis and neonatal diarrhoea was higher in herds producing only weaners ("weaner herds") than in herds with combined production. The mean disease incidence in herds providing breeding stock for the Norwegian Pig Breeders' Association ("breeding herds") was at the same level as in ordinary combined production herds. There was no consistent relationship between changes in disease incidence and herd size, though the incidence of the MMA-syndrome was lower in the largest herds.