Experimental challenge of pregnant gilts with swine influenza virus after vaccination

Inactivated swine influenza virus was concentrated by filtration. Two 5 ml doses given subcutaneously two to three weeks apart to SPF gilts of breeding age of bred gilts was antigenic as measured by the hemagglutination-inhibition (HI) test. Higher HI titers of longer duration were produced in unvaccinated gilts after experimental challenge. Vaccinated gilts reverted to negative (less than 1:20) HI tests after challenge. Pigs from vaccinated gilts were heavier when weaned at five weeks of age than pigs from unvaccinated gilts. No swine influenza virus was isolated after challenge from placentas or pigs born dead or that died after farrowing.