Abstract
Early Pregnancy Factor (EPF) has been detected in the pregnant sera of almost all the species examined. Yet no EPF of mare sera had been reported prior to this study, because the method of examination had not yet been established. The present study was carried out to examine various factors which influence the rosette inhibition test of mares and to establish a reliable assay system for Rosette Inhibition Titre (RIT). The following items were found optimal for the detection of RIT in mare sera: human erythrocytes (red blood cells) showed the best reactivity among human, sheep, and rat erythrocytes; the ratio of lymphocytes to erythrocytes of 1:20 was proven to show better results; and Guinea Pig Complement (GPC) was not necessary. When the rosette inhibition test was performed on 10 pregnant and 9 nonpregnant sera, the RIT values ranged from 6 to 8 (7.2 ± 1.0) in nonpregnant sera, and from 9 to 12 (9.5 ± 1.0) in pregnant sera, with a significant difference (p<0.01). These results suggested the availability of the RIT for pregnant mare sera as an index of early detection of pregnancy in mare.
