Management of twin conceptuses by manual embryonic reduction: comparison of two techniques and three hormone treatments.

One hundred mares carrying twin conceptuses between gestation days (GD) 12 and 30 were assigned to 4 groups. Group-1 mares (n = 20) were given a placebo (sterile saline solution, IV, and sesame oil, IM). Group-2 mares (n = 32) were given a single dose of progesterone (625 mg, IM) in sesame oil. Group-3 mares (n = 28) were given multiple progesterone treatments (625 mg, IM) at 6-day intervals until GD 42. Group-4 mares (n = 20) were given a single treatment of flunixin meglumine (500 mg, IV) and progesterone (625 mg, IM). Each group was further assigned to equal subgroups A and B according to the age of the embryos. In subgroup A, with embryos at GD 12 to 16, embryonic vesicle rupture was performed after the selected conceptus was moved to the tip of a uterine horn. In subgroup B, with embryos at GD 17 to 30, embryonic vesicle rupture was performed on the selected conceptus in situ. An additional 6 mares carrying single conceptuses (GD 12, 14, 16, 20, 25, and 30) were used as subjects for sham embryonic vesicle rupture. Both rupture techniques usually caused the release of prostaglandin (PG) F2 alpha for up to 90 minutes. Amounts of PGF2 alpha were directly correlated with the pressure required to effect embryonic vesicle rupture. Sham embryonic vesicle rupture attempts caused small PGF2 alpha releases after each manipulation, which rapidly returned to basal values. All 6 mares were still pregnant at GD 42. Flunixin meglumine inhibited PGF2 alpha release after embryonic vesicle rupture, regardless of the technique.(ABSTRACT TRUNCATED AT 250 WORDS)