Impact of PRRS virus infection in the replacement gilts on number and development of follicles in the ovarian tissues

Abstract

Replacement gilts are a major source of introducing the porcine reproductive and respiratory syndrome (PRRS) virus into the swine breeding herd. The objective of the present study was to determine the prevalence of PRRS virus antigen by detection in the ovary of gilts culled due to reproductive disturbances. Ovarian tissues were collected from 100 Landrace x Yorkshire crossbred slaughtered gilts in Thailand. PRRS virus antigen in the ovarian tissues were detected by using immunohistochemistry. On average, the gilts were culled at 277 days of age at a body weight of 148 kg. Of these gilts, 75 had attained puberty and 25 had not attained puberty. PRRS virus antigens were detected in the macrophages within the ovary. The histological morphology of macrophages containing the PRRS virus in ovarian tissue was similar to that found in lung tissue. Of all the ovarian tissues (n = 100), the PRRS virus was detected in 70 (70.0%) ovaries. The detection frequency of the PRRS virus in the ovarian tissue of gilts did not differ significantly among the culling reasons (P = 0.496). The gilts that had exhibited standing oestrus had a lower PRRS virus detection than those that had never exhibited standing oestrus (62.8% versus 92.0%, respectively, P = 0.005). Gilts with a body weight of 151 – 160 kg had a higher frequency of PRRS virus detection (89.5%) than gilts with a body weight of ≤130 kg (52.9%, P = 0.025) and 131–140 kg (50.0%, P = 0.032). The ovulation rate in the ovary containing the PRRS virus tended to be lower than the ovary without the PRRS virus (14.8 and 16.7 CL, respectively, P = 0.196). These findings indicated that the natural exposure to PRRS virus in the replacement gilts caused an existence of the virus in the ovarian tissues and may subsequently influence the ovarian function.