Impact of a natural bluetongue serotype 8 infection on semen quality of Belgian rams in 2007

In 2006, bluetongue (BT) virus serotype 8 emerged in northern Europe and numerous ruminants were affected in the following year. Infertility in males is one of the consequences of BT, although its severity and duration after natural infection has not been documented. In this report, the impact of BT-8 on clinical signs and semen quality of naturally infected rams is described through a longitudinal study of two Belgian ram populations (n=12 and n=24) and a cross sectional study in a further ram population (n=43). Macroscopic semen characteristics, semen concentration, motility, percentage of living and dead spermatozoa were assessed in 167 semen samples collected on 1-6 occasions from 79 BT-8 infected rams within 5-138 days after onset of clinical disease. These were compared with healthy control animals. Significant changes in all variables were observed after natural BT-8 infection. Total recovery occurred around 85 days after clinical disease in animals undergoing a close follow-up of semen quality. Good correspondence between the results of the longitudinal and cross sectional studies suggests that semen quality of BT-8 affected rams reached normal references values 63-138 days after clinical diagnosis of BT. In addition, semen concentration seems to be a sound epidemiological indicator of ram semen quality.