Objective—To assess pregnancy and live foaling rates after reduction of twin pregnancy via transvaginal ultrasound-guided aspiration (TUA) in mares and evaluate effects of gestational period, localization of conceptuses, fluid aspiration volume, and combination of TUA with embryonic or fetal puncture on these outcomes.
Animals—44 mares pregnant with twins (25 to 62 days of gestation).
Procedures—TUA was performed in all mares and combined with embryonic or fetal puncture in 13. Follow-up ultrasonographic examinations were performed by referring veterinarians. Effects of gestational period and TUA-related variables on pregnancy and foaling rates were assessed.
Results—Singleton pregnancy (32/44 [73%]), persistent twin pregnancy (3/44 [7%]), or loss of both conceptuses (9/44 [20%]) was confirmed 5 to 7 days after TUA. Two mares with persistent twin pregnancy underwent another TUA, and 1 underwent prostaglandin F2α–induced abortion; these were excluded from subsequent analyses. Eighteen of 24 mares reevaluated 3 to 4 weeks after TUA were pregnant with 1 conceptus. Twenty of 41 (49%) mares delivered live singleton foals. Gestational period of TUA did not affect early pregnancy rates. Foaling rate for mares that underwent TUA after day 42 (0/5) was lowest of all groups and was significantly lower than that of mares that underwent TUA between days 31 and 35 (9/14). Three of 13 mares that underwent TUA with embryonic or fetal puncture delivered live foals, compared with 17 of 28 that underwent TUA alone. Effects of other variables were nonsignificant.
Conclusions and Clinical Relevance—TUA was effective for reduction of twin pregnancy in mares, with best results achieved before gestational day 43.