Abstract:
Under field conditions, majority of the replacement gilts are culled due to anoestrus. The ovaries in most gilt are non-cyclic and contain numerous small and medium size follicles, but fail to ovulate and attain puberty. Alteration of ovarian steroids production which regulates reproductive function may be the cause. To understand the mechanisms underlying follicular maturation, proliferating and apoptotic cell markers, estrogen receptor β (ERβ) and luteinizing hormone receptor (LHR) were investigated. Proliferating cell nuclear antigen (PCNA) was used to determine the number and type of follicles in gilt ovarian tissues associated with the number of follicles and reproductive performances. The percentage of apoptotic cells and the immunoexpression of ERβ were examined using terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) and anti-ERβ immunohistochemistry, respectively. Additionally, the LHR immuno-staining in preantral and antral follicles was investigated. It was found that the proportions of primordial, primary and growing follicles were 64.2%, 32.7% and 3.1%, respectively. The number of primary follicles was positively correlated with body weight but negatively correlated with age at first observed oestrus (P < 0.05). Gilts with a heavy body weight and attain puberty early have a higher density of primary follicles. The proportion of apoptotic cells in preantral follicles was higher than antral follicles. Moreover, the proportion of apoptotic cells in non-cyclic gilts was higher than cyclic gilts in both granulosa and theca cell layers (P < 0.001). Apoptosis associated with anoestrus or non-cyclic gilts. In addition, the ERβ immunoexpression in the theca cells of antral follicles in non-cyclic gilts was lower than that in cyclic gilts (P < 0.001). The LHR immuno-staining in the theca interna layer of antral follicles was higher than preantral follicles (65.4% vs 38.3%, P < 0.01) and it was higher in follicular phase than the luteal phase (58.6% vs 45.2%, P < 0.05). In conclusion, inactive ovaries in the anoestrus culled gilts were associated with low density of primary follicles, high proportion of apoptotic cells and poor immmunoexpression of ERβ and LHR.
