Use of an intra-uterine glass ball protocol to extend luteal function in mares

SUMMARY A 25- or 35-mm diameter glass ball was placed in the uterus of mares to observe the effect on interovulatory interval, luteal function, estrous behavior, the endometrium, and subsequent fertility. The 25-mm glass ball was spontaneously expelled from the uterus of 6 of 12 mares (50%), whereas none of the 35-mm glass balls was expelled. Teasing results were consistent with the concentration of circulating progesterone. Luteal function was extended in 7 of 18 mares (39%) maintaining a glass ball, whereas an extended luteal period occurred in 4 of 32 mares (13%) observed as controls. Extended luteal function occurred in 7 of 62 diestrus periods (11%) among mares following ball placement, whereas 4 of 50 diestrus periods (8%) were extended in control cycles. The mean luteal life span in mares with a glass ball and extended luteal function was 87 days (range, 76 to 109 days); there were no significant differences in length of luteal function in both groups of mares that received the 2 different ball sizes. Endometrial changes observed between preplacement and postremoval samples were minimal. When mares were bred in the season subsequent to glass ball removal, 17 of 23 (74%) conceived. Placing an intrauterine glass ball in a mare may be an alternative to exogenous hormone therapy to prevent cycling in some mares. Luteal function was extended to nearly 90 days in approximately 40% of mares. The 35-mm diameter glass ball appeared to have an advantage for retention over the 25-mm size. Results of our study could not completely