FIG. 2.

Circulating concentrations of progesterone in nonpregnant (A) and pregnant (B) fertility-classified heifers. Fertility-classified heifers were synchronized to estrus and bred by artificial insemination (AI) at 12 and 24 h postestrus with semen from a high-fertility bull. Pregnancy was determined on Days 28 and 35 by ultrasound. An effect of day (P < 0.0001) was detected because progesterone concentrations increased after ovulation. There was an effect of day (P < 0.0001), but not fertility class (P = 0.86), on progesterone concentrations for HF and SF heifers diagnosed pregnant through Day 36. Progesterone concentrations were higher in SF than HF heifers on Day 36 (P = 0.04, day × fertility class). Data is presented as least squares means (LSM) with the standard error of the mean (SEM).