(2014) reported a difference between primiparous and multiparous cows, where the optimal time for AI relative to onset of estrus was 13 to 16 h postalert, whereas primiparous cows had relatively stable conception risks when being inseminated any time between 0 to 16 h postalert. Using visual detection, Van Eerdenburg et al. (2002) reported that cows that ovulated between 0 and 24 h post-AI had greater conception rates and also had more estrous expression than those that ovulated before insemination or later than 24 h.