Plasma progesterone concentrations in each pregnancy status of cattle after AI or ET. Plasma progesterone concentration (mean ± S.E.M.) on days 7, 12, 16, 18, 21, and 25 after standing estrus in pregnant, extended interestrous interval (≥ 25 d, eIEI), and normal interestrous interval (< 25 d, nIEI) cattle after AI (A) or ET (B). Comparisons were made within each day. Different letters indicate a significant (P < 0.05) difference between values.