Importance of twinning in horse breeding

Twinning is highly undesirable, even considered to be a pathological condit ion in horse. In most cases twin pregnancies terminate in abortion, stillbi rth, perinatal losses, or delivery of weak and deformed foals. Genetic fact ors, feeding, intrauterine nutrition, age and possibly uterine size influen ces the occurrence of twinning in mares. Data of breeding (pedigree analysi s) from 1963 to 1994 and of twinning reproduction management (sonographic a nd rectal diagnosis, prostaglandin induced embryonic death and restricted f eeding) from 1995 to 2000 were collected and analysed in a Hungarian Thorou ghbred stud. High twinning rate (4%) was succesfully managed and decreased to 1% without selection of twinners. A hereditary predisposition (frequent twinning) was revealed and proved in various mare family lines and amoung d oughters of presumebly carrier stallions (Table and Figure). A possible mod e of inheritance (major gene?) as well as genetic and other practical metho ds of twinning prevention are discussed in details.