Progesterone, LH, Estrus and Ovulation after Prostaglandin F2 in Heifers

Abstract

PGF2α (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 PGF2α 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 PGF2α during diestrus, one heifer failed to respond; the other five responded similarly to those given im PGF2α during diestrus except that luteolysis was more variable and delayed about 1 or 2 days compared to that after im PGF2α. PGF2α (im) was neither luteolytic nor luteostatic in metestrus. We conclude that 30 mg PGF2α is luteolytic during diestrus in heifers, but im administration is more effective than intravaginal administration.