Sub-clinical swine fever: a survey of neutralizing antibodies in ther sera of pigs from herds having reproductive failures.

Sera harvested from breeding farms where reproductive failures were observed but where swine fever vaccination was not carried out, where tested for the presence of neutralizing antibodies specific for swine fever virus. Neutralization tests were performed in tissue culture using two viruses strains: the american serological variant "331" strain isolated by MENGELING (1969) and the virulent "normal strain" Alfort. For comparison, sera harvested from healthy, vaccinated and unvaccinated breeding farms were also tested.