All cows were subjected to the standard Ovsynch timed
AI protocol , of which 718 were enrolled for the first
postpartum AI and 1,007 were enrolled during a
resynchronized insemination after diagnosed as nonpregnant.
Cows receiving the first AI postpartum had their
estrous cycle presynchronized with injections of 25 mg
PGF2a intramuscularly administered 14 days
apart, at 38 3 and 52 3 days in milk in herds 1, 2,
and 4, or at 44 3 and 58 3 DIM in herd 3.