The pregnancy loss are common problems in the creation of equine, being the cause of concern among professionals, the numerous economic losses to the agribusiness sector. Early miscarriages are more incidents late, being attributed to maternal, environmental and embryonic factors. The factors include maternal reproductive tract changes, the mare's age, progesterone deficiency, when the cover reproductive status, failure in maternal recognition of pregnancy covering the foal heat, among others. Environmental factors include maternal stress, nutrition and effect of semen. Late pregnancy losses are fewer incidents and were attributed mainly to infectious disorders related to fetal-placental interactions, as ascending placentitis of origin. Equine herpesvirus type I and leptospirosis are the most common infectious causes, making essential health control and vaccination of the squad. Due to the alarming figures, the aim of this study, a literature review describing the main causes of pregnancy loss in the equine species.