Ultrasound-guided biopsies of corpora lutea have been previously used for research purposes in the mare and cow. However, the health effects and fertility after transvaginal luteal biopsies (TVLB) or transvaginal ovarian biopsies (TVOB) obtained for diagnostic purposes in cases of suspected ovarian tumors have not been previously evaluated in the horse. The aim of this study was to determine the effects on health and fertility of TVLB and TVOB in mares; 53 mares were included in the study (11 control non-biopsied mares, 37 TVLB mares biopsied on one or more of the following Days 8, 10, 12, 15, 21, and 5 TVOB mares with ovarian abnormalities), resulting in a total of 108 TVLB and TVOB cycles and 183 procedures. Mares were divided into Groups 1 to 3 by the number of TVLB per estrous cycle (mare in Group 1 had 1 TVLB procedure, mares in Group 2 had 2 TVLB procedures, and mares in Group 3 had 3 TVLB procedures). Group 4 comprised TVOB mare cycles with ovarian abnormalities (n = 5). Mares were examined to determine day of ovulation (Day 0) and the presence of a corpora lutea using transrectal ultrasonography. Mares were sedated, and an ultrasound-guided transvaginal biopsy was performed of luteal or ovarian tissue. Health effects of TVLB or TVOB were assessed by daily rectal temperatures, appetite, and general demeanor for 72 hours post-procedure, and 3 mares were examined at necropsy. Fertility was not significantly different in control and TVLB Groups 1 to 3 (P = 0.7648) and in the first or subsequent cycles where the ovulation was from an ovary that had a previous TVLB (P = 0.7147). A TVLB on Day 8 post-ovulation may induce an early return to estrus. In conclusion, the TVLB or TVOB procedure had no effect on health and fertility in this study if the procedure was correctly performed with good technique. Because of the low number of cycles (n = 37), the fertility data should be interpreted with caution. The TVOB may be applied in the diagnosis of mares with ovarian abnormalities, and no adverse health effects were associated with TVOB of mares with granulosa theca cell tumor.
