Abstract
When prostaglandin F2α (PGF2α) was injected (im) at three different stages of the cycle, estrus was synchronized within an 80-h period in a progressively, but nonsignificantly, higher percentage of heifers with each advancing stage: 86.0% at d 7, 90.0% at d 11 and 98.0% at d 15. Estrus was exhibited within a 48-h period for heifers treated on d 7, but extended over a 72-h period for heifers treated on either d 11 or 15. Stage of cycle when PGF2α was injected not only influenced the degree of estrous synchrony, but also influenced (P<.001) the time of estrous onsets. Within the 24-h interval from 32 to 56 h postinjection, the percentage of heifers exhibiting estrus from treatment on d 7, 11 or 15 varied widely: 88.4, 13.3 and 73.5, respectively. Induction of estrus was complete, or nearly so, by 72 h postinjection for heifers treated during the early (d 7 = 100.0%) or late (d 15 = 95.5%) stage of the cycle, but reached only midpoint for midcycle injections (d 11 = 48.9%), with the remaining one-half (51.1%) occurring 72 to 104 h later. Pregnancies arising from the first through the fifth services among the 150 PGF2α-treated heifers were as follows: 76.0, 10.0, 6.7, 4.0 and .7%, plus failure of pregnancy in 2.7%. These percentages were not different (P>.50) from those among the 50 control heifers. Copyright © 1984. American Society of Animal Science . Copyright 1984 by American Society of Animal Science