Previous reports have discussed the optimal timing of AI relative to estrus behaviors. The most optimal interval for AI after the onset of visually detected estrus was 7 to 12 h (Hall et al., 1959). Another study reported the greatest conception rates for inseminations occurring 4 to 12 h after the onset of estrus using a pressure-sensing system (Dransfield et al., 1998). Using an automated activity monitor (AAM), Stevenson et al.