Progesterone,LH,Estrus and Ovulation after Prostaglandin F 2α in Heifers 1

Summary

PGF_2α (30 mg Tham salt) was injected im into five heifers during diestrus (Days 9 to 13 of the estrous cycle), im into six heifers during metestrus (Day 3), and intravaginally into six heifers during diestrus. After im PGF_2α during diestrus, (a) luteal diameter decreased from 2.3 ± 0.1 cm to 1.8 ± 0.1 cm at 24 hr and to 0.6 ± 0.3 cm at 72 hr, (b) blood serum progesterone fell from 4.0 ± 0.4 ng/ml to 1.5 ± 0.2 ng/ml at 12 hr and to 1.0 ± 0.2 ng/ml at 72 hr, and (c) estrus began at 74 ± 3 hr and ovulation occurred at 104 ± 6 hr. After intravaginal PGF_2α during diestrus, one heifer failed to respond; the other five responded similarly to those given im PGF_2α during diestrus except that luteolysis was more variable and delayed about 1 or 2 days compared to that after im PGF_2α. PGF_2α (im) was neither luteolytic nor luteostatic in metestrus. We conclude that 30 mg PGF_2α is luteolytic during diestrus in heifers, but im administration is more effective than intravaginal administration.