(Savio et al., 1988) and thus a longer interval to estrus compared with cows in earlier or later stages of
the estrous cycle. Comparable with the short interval to estrus when beef cows were treated with PGF2α on
d 6 to 9 of the cycle in the present study, dairy heifers treated on d 5 to 7 of the cycle (Johnson, 1978; Watts and Fuquay, 1985), and beef cows treated on d 5 to 9 of the estrous cycle (King et al., 1982) commenced estrus in 57 to 60 h after treatment. Stevenson et al. (1984) found a 61-h interval to estrus when Holstein heifers were treated with PGF2α on d 14 to 16 of the cycle.