Fig. 1

Macroanatomical images of the bovine CL. The CL was cut through an equatorial plane. The color of the CL during the early-luteal (EL) stage is bloody or flesh and size was less than 2.0 cm (a). The CL during the mid-luteal (ML) and late-luteal (LL) stages increased in size to more than 2.0 cm in diameter (b, c). The color of the CL during the ML stage is flesh or orange (b), while that during the LL stage turns to yellow (c). Regressed CLs are small with a diameter of less than 1.5 cm and show various colors such as ocher (d), brown (e), or white (f). Arrows in E and F show connective tissue in the CL parenchyma