The effect of prostaglandin F(2α) during various stages of the oestrous cycle of beef heifers

Abstract

The effects of prostaglandin F(2α) on peripheral plasma progesterone and estrogen levels, incidence of estrous cycle alteration, and fertility were examined in 30 beef heifers. The PGF(2α) was administered by insertion of an insemination pipette into the lumen of the uterus during 3 periods of the estrous cycle: Days 3 to 5, Days 9 and 10, and Days 16 and 17. Estrus occurred within 2 to 5 days in all animals treated except those treated on Days 3 and 4. Plasma progesterone levels had fallen significantly by the day following treatment and continued to fall in those heifers returning to estrus. As progesterone fell, plasma estrogen increased to a peak level on the day before or the day of estrus. The hormone patterns were quite similar to those of the untreated animals as they approached estrus and during the 16 day period after mating. The pregnancy rate was significantly lower in the treated heifers than in the untreated heifers. This was probably due to uterine infections rather than to the drug per se.