Artificial insemination of cows with semen in vitro contaminated with Neospora caninum tachyzoites failed to induce neosporosis

Neosporosis is a major cause of abortion in cattle all over the world. Congenital transmission as well as horizontal transmission by ingestion of oocysts has been described. The detection of Neospora caninum DNA in bull semen warrants the investigation of possible transmission through the use of contaminated semen. In this experiment four cows were artificially inseminated with frozen-thawed semen contaminated in vitro with viable N. caninum tachyzoites (group A) and four control cows were inseminated with tachyzoites-free frozen-thawed semen, from the same bull (group B). Serum samples were collected 15 days before the artificial insemination (AI) and at days 10, 14, 21, 28, 45, 60 and 75 post-insemination. All sera samples were tested for neosporosis by direct agglutination test (DAT). Three of the cows from group A had negative DAT titers (≤1:20) in all of the samples, while the fourth cow from this group had a low titer of antibodies (1:80) at day 10, and became negative at day 45, suggesting a stimulation of the immune system by the tachyzoites placed in uterus, rather than the induction of an infection. All of the cows from group B had negative DAT titers (≤1:20) in all of the samples. These results suggest that transmission of neosporosis by artificial insemination with frozen-thawed semen is an unlikely event.