This study aimed to (1) identify the status of reproductive tract of repeat-breeder heifers (RBH) ultrasonography, as well as (2) determinethe variations in steroid hormones, oxidative stress biomarkers, and cell-free RNA in serum.These culled animals from400 heifers at the breeding stationwere examined ultrasonography, and whole blood samples were collected. Theultrasonic diagnosed heifers as paraovarian cyst (POC, n=18) associated with genital pathological conditionswere 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 withCL absence (POC-CL). Heifers with POC-CLhad 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 proteinslevels recorded lower valuesin POC+CL compared to that in follicular phase. There was a significant positive relationship between POCsize, 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.