Success Rate of Post-Fixation Twin Reduction Using Cranio-Cervical Dislocation

1. Introduction
The establishment and loss of twins, after 35 days of gestation, often results in a mare that is barren for a year and the associated economic loss. The incidence of twin births in the past has been documented as occurring in 1–2% of the equine population,¹  with twinning accounting for 6 –30% of abortions in the mare.^{2– 4}  Abortion or still birth resulted in 64.5% of twin conceptuses that were maintained for ≥8 mo, with only 14% of surviving foals reaching the second week of neonatal life.²  In another study, only 11% of 130 mares carrying twins produced viable foals, and only 38% of these mares produced viable foals the following year.⁵  When twins are present, gestation proceeds normally until the conceptuses begin to compete for uterine space or placenta. With or without mummification, death of one fetus leads to abortion, usually between 5 and 9 mo of gestation.⁶  Lactation commonly occurs after one foal dies, causing premature mammary gland development.⁶  If one or both foals are born alive, the mare may require assistance. Surviving foals are usually weaker, more susceptible to infection, and slower to develop than singletons. [...]