Immediately after the end of Exp. 2 (d 28),
heifers (mean BW = 462 ± 14 kg) received a new CIDR
and were evaluated via transrectal ultrasonography (5.0-
MHz transducer, 500V; Aloka) to confi rm the absence
of a corpus luteum. Again, none of the heifers ovulated
and developed a corpus luteum during Exp. 2 and were
therefore immediately assigned to Exp. 3 (d 28 to d 55).