sentences:  However, subsequent foals that are by the same stallion or a different stallion that carries the same incompatible blood group, are at risk, and as such this disease is most commonly seen in foals out of multiparous mares.Additionally, exposure can occur due to placental abnormalities in early gestation that allow the foal's red blood cells to leak into the mare's circulation, or if the mare is exposed through blood transfusion.Because this exposure occurs well before the foal receives colostrum, the mare will have circulating antibodies at the time of parturition and therefore the foal is at risk of developing NI.