Granulosa cell proliferation in the gilt ovary associated with ovarian status and porcine reproductive and respiratory syndrome virus detection

The aims of the present study were to quantify the number of follicles and determine granulosa cell proliferation in the ovaries of gilts in relation to ovarian status and porcine reproductive and respiratory syndrome (PRRS) virus infection. Ovarian tissues were obtained from 37 Landrace × Yorkshire crossbred gilts aged 270.7 ± 24.5 days and weighing 144.5 ± 15.0 kg (27 cycling and 10 prepubertal gilts). PRRS virus was detected using immunohistochemistry, and the ovaries were classified as negative (n = 17) or positive (n = 20) to PRRS virus. Granulosa cell proliferation was determined by proliferating cell nuclear antigen (PCNA) immunostaining. The proportion of PCNA-expressing granulosa cells in pre-antral (n = 197) and antral follicles (n = 76) was determined using Image-Pro® Plus software. The number of follicles in ovarian tissue containing PRRS virus did not differ significantly compared with those without PRRS virus. Granulosa cell proliferation was influenced by the type of follicle (P < 0.05), ovarian status (P < 0.05), the age of the gilt (P < 0.05), and the interaction between ovarian status and PRRS virus detection (P = 0.06). Granulosa cell proliferation in cycling ovaries was higher than in prepubertal ovaries (84.0 ± 5.1 and 35.2 ± 8.0 %, P < 0.05) in gilts without PRRS virus but not in ovaries containing PRRS virus (68.5 ± 4.3 and 44.4 ± 9.2 %, P > 0.05). It can be concluded that the detection of PRRS virus in the gilt’s ovarian tissue was not associated with the number of follicles but was associated with the proliferation of granulosa cells in the cycling ovaries. This might subsequently cause delayed follicle development, reduced oocyte quality, and infertility in gilts.