This study aimed to (1) identify the status of reproductive tract of repeat-breeder heifers (RBH) ultrasonography, as well as (2) determine the variations in steroid hormones, oxidative stress biomarkers, and cell-free RNA in serum. These culled animals from400 heifers at the breeding station were examined ultrasonography, and whole blood samples were collected. The ultrasonic diagnosed heifers as paraovarian cyst (POC, n=18) associated with genital pathological conditions were compared with groups of control heifers at follicular(n=6), luteal (n=6), and early pregnant (n=10). The POC appeared as anechoic circumscribed masses located nearby, but separated from the ovary. Follicular number, corpus luteum size, serum cell-free RNA, and ovarian steroids were not affected by POC, although dominant follicle size tended to be lower (P= 0.069)in POC with CL absence (POC-CL). Heifers with POC-CL had lower MDA levels than pregnant ones. Buffaloes that had POC in the presence of CL (POC+CL) were found to have higher SOD activity than luteal and pregnant cases. Total serum proteins levels recorded lower values in POC+CL compared to that in follicular phase. There was a significant positive relationship between POC size, and GPx activity and CL size, but negative correlations with dominate follicles size. The POC might interfere with ovarian function, via alterations in antioxidant levels.