Semen quality of stallions challenged with the Kentucky 84 strain of equine arteritis virus

Equine arteritis virus (EAV) is the causal agent of equine viral arteritis (EVA), a respiratory and reproductive disease of equids. Some strains of EAV can cause fever, leukopenia, and dependent edema of the limbs, scrotum, and preputium in the acutely infected stallion. We hypothesized that fever and scrotal edema observed during the acute phase of the infection, but not the presence of EAV, have an adverse effect on semen quality. A group of seven stallions were intranasally inoculated with the Kentucky 84 (KY84) strain of EAV. Stallions were monitored for clinical signs of EVA until 42days postinoculation (dpi). Semen was collected every other day for the first 15days and 2 times a week up to 79dpi. Additional samples were collected at 147, 149, and 151dpi. Semen from each stallion was evaluated on the basis of motion characteristics, total number of spermatozoa, membrane integrity, and morphology. Virus infectivity titers were determined in RK-13 cells. Significant decreases in sperm quality were observed between 9 and 76dpi. LOWESS (locally weighted scatterplot smoothing) curves for each horse were fit and integrated to quantify spermatozoa exposure to fever, virus, and edema over a period of 67days before each ejaculation. Linear mixed models were then fit to isolate the effects of each factor on semen quality. Scrotal edema and fever were found to exert independent effects on all the semen quality parameters (P≤0.002), whereas virus seems to exert little to no direct effect, as virus titers remained high long after semen quality returned to baseline.