STUDIES ON OCCURRENCE OF SPONTANEOUS TWIN PREGNANCIES IN MARES, WITH REFERENCE TO PMSG FORMATION

An account is given in this paper of studies conducted on some 300 mar es that are exclusively used for PMSG collection at Impfstoffwerk Dess au-Tomau. A total of 3552 pregnancies was recorded between 1975 and 19 85, among them 82 twin pregnancies. Repetitive twin pregnancy occurred to seven mares and was more frequent in animals aged 13 to 14 years. Twin pregnancy was increased with significance, following serving in F ebruary. Thirty-five twin pairs were examined, with 65.7% of them bein g of both sexes. PMSG formation in mares with spontaneous twin pregnan cies was higher than that in animals with single pregnancies.