Transient adverse effects of an attenuated bluetongue virus vaccine on the quality of ram semen.

This study investigated the effects of the vaccination of rams with a serotype 2 bluetongue virus vaccine on the quality of their semen. One group of 23 rams was vaccinated on days 0 and 47, and 23 rams were left unvaccinated. Samples of blood, serum and semen were collected regularly in order to detect the virus genome, and to compare the quality of the semen from the vaccinated and unvaccinated rams. Segment 10 of the genome of the vaccine strain was detected in the blood of the vaccinated animals by reverse transcriptase-PCR (RT-PCR) on days 7, 13 and 19 after the first vaccination, but no virus was isolated from the RT-PCR-positive blood or from any of the semen samples from the vaccinated animals. There was a significant decrease in the concentration and motility of the spermatozoa and an increase in the proportion of abnormal and dead spermatozoa after the first vaccination; however, after the second vaccination only smaller, non-significant changes were observed. On day 69, the quality of the semen of the vaccinated animals was not significantly different from that of the controls.