Different humoral mechanisms against Neospora caninum infection in purebreed and crossbreed beef/dairy cattle pregnancies.

The antigen-specific IgG subclass response may be a convenient indicator of the underlying nature of T helper cell regulation. The aim of the present study was to identify possible differences in Neospora caninum-specific total plasma IgG, IgG1 and IgG2 antibody levels in purebreed and crossbreed pregnancies throughout gestation in beef and dairy cattle chronically infected with N. caninum. Comparisons were also made between aborting and non-aborting dams. The population examined comprised 96 pregnant parous cows seropositive for N. caninum. Plasma antibodies were determined on Days 90, 120, 150, 180 and 210 of gestation or until abortion. Of the 96 pregnancies examined, 12 ended in abortion. None of the 14 Holstein-Friesian (HF) cows inseminated with HF semen (HF-HF group) aborted, whereas 6 (11.0%) of the 54 HF cows inseminated with Limousin semen (HF-L group) and 6 (21.4%) of the 28 Rubia Gallega (RG) beef cows inseminated with RG semen (RG-RG group) aborted. In the 84 non-aborting cows, a significant positive effect of gestation day was observed on total IgG, IgG1 and IgG2 antibodies levels (P<0.0001 for the three variables). In RG-RG cows, significantly higher levels of IgG (P=0.003; d.f.=2; F-value=6.41), IgG1 (P<0.001; d.f.=2; F-value=10.55) and IgG2 (P=0.004; d.f.=2; F-value=5.82) antibodies against N. caninum were recorded throughout gestation compared to the other groups, whereas the levels of these antibodies were significantly lower in HF-HF on Days 180 and 210 of gestation. In aborting cows, significantly lower IgG (P=0.001; d.f.=1; F-value=25.21) and IgG2 (P=0.001; d.f.=1; F-value=20.39) antibody levels were observed in the RG-RG cows compared to the HF-L cows, whereas no significant effect on IgG1 antibody levels was detected in the two groups with aborting animals (RG-RG and HF-L). Our findings indicate that humoral mechanisms against N. caninum infection and abortion differ in purebreed pregnancies and crossbreed pregnancies in beef/dairy cattle.