Indirect conclusions can be drawn only about the time frame during which maternal recognition of pregnancy occurs. The conceptus has to be recognized before Day 14 after ovulation, as this is the time that luteolysis is initiated in the mare (Ginther et al. 2011). Although expression of oxytocin receptors is similar for nonpregnant and pregnant mares on Days 10 and 12 after ovulation, expression of oxytocin receptors is less for pregnant than cyclic mares on Day 14 after ovulation (de Ruijter-Villani et al. 2014; Sharp et al. 1997; Starbuck et al. 1998). Continuous infusions of oxytocin from 8 days after ovulation prolong luteal phase, whereas continuous infusions of oxytocin from 10 days after ovulation initiate luteolysis (Stout et al. 1999), indicating that maternal recognition of pregnancy is initiated by Day 10 postovulation. Wilsher and coworkers (2010) recently suggested reevaluation of the concept that maternal recognition of pregnancy occurs on or before Day 10. Surprisingly, all six asynchronous transfers of 10-day-old blastocysts into recipient mares on Day 12 of diestrus resulted in establishment of pregnancy and survival of the conceptus to the “heartbeat stage” of development of the embryo (end of observation period). Notwithstanding, various mechanisms lead to luteal maintenance when using repeated/continuous administration of oxytocin versus transfer of a blastocyst as in vitro factors secreted by the conceptus lead to a rapid (within 24 h) reduction in secretion of PGF2α by endometrial explant cultures (Ealy et al. 2010). It seems likely that the mechanism leading to luteal maintenance via repeated or continuous treatments with oxytocin must be initiated well before maternal recognition of pregnancy occurs.