Relationship between IFNγ production, antibody and hormone levels in naturally Neospora caninum-infected pregnant dairy cows

Neosporosis is a widespread parasitic disease caused by Neospora caninum, an intracellular protozoan parasite. It causes economic losses due to reproductive failure. The potential relationship between pregnancy outcomes and levels of IFNγ, hormones, and antibodies in naturally N. caninum-infected cows was examined in the blood samples collected every 2 or 4 weeks in 26 pregnant cows from 4 different farms. The mean S/P value of seropositive nonaborting animals (n = 14) reached peak levels 15 weeks prior to parturition, and declined thereafter to parturition. The S/P value 13 weeks prior to abortion in seropositive aborting cows (n=3) remained at high levels, and abortions occurred at 20 (142 days), 26 (185 days), and 28 weeks (199 days) after artificial insemination. IFNγ levels in the seropositive non-aborting group varied by individuals and gestational periods; IFNγ levels stayed at elevated levels or increased abruptly close to abortion in seropositive aborting cows. IFNγ level patterns in the seronegative group (n = 9) were similar to the seropositive non-aborting group, although IFNγ amounts were lower than the seropositive group. The mean progesterone levels in the seropositive non-aborting and seronegative groups decreased markedly 7 weeks priorto parturition. The mean progesterone levels 5 and 7 weeks prior to abortion were lower than the other groups 5and 7 weeks prior to parturition. The mean 17β-estradiol levels in the seropositive aborting cows increasedclose to abortion; the produced amounts were lower than those of seropositive non-aborting and seronegative groups close toparturition. These results suggested that lower levels of progesterone and β-estradiol in Neospora-infected cows may lead to increases in IFNγ production and in turn may result in abortion.