Volume of luteal tissue and concentration of serum progesterone in cows bearing homogeneous corpus luteum or corpus luteum with cavity

Ultrasonographical examinations of ovarian structures were performed in 27 inseminated cows at estrus days and on days 4, 9, 20, 25, 30, and 40 after ovulation. Three cows were used twice. Corpora lutea (CLs) with a cavity were compared with homogeneous CLs in pregnant and nonpregnant cows. Diameters and volumes of CLs and cavities, as well as volumes of luteal tissue and concentrations of serum progesterone were determined. The volumes of the structures were calculated using a mathematical formula for a rotary ellipsoid. Homogeneous CLs and CLs with a cavity and their luteal tissue reached a maximum volume in nonpregnant and pregnant cows on day 9 after ovulation. At this time, CLs volumes were 7.52 ± 3.14 (homogeneous CLs, n = 4) and 4.54 cm3 (CLs with a cavity, n = 1) in nonpregnant cows, and 6.05 ± 1.71 (homogeneous CLs, n = 10) and 9.54 ± 2.67 cm3 (CLs with a cavity, n = 15) in pregnant cows. The volumes of luteal tissue were 7.52 ± 3.14 and 4.33 cm3 in nonpregnant cows and 6.05 ± 1.71 and 8.62 ± 3.46 cm3 in pregnant cows. Concentrations of progesterone in peripheral blood in pregnant cows bearing a homogeneous CLs or CLs with a cavity on day 9 were 3.15 ± 0.69 ng ml−1 and 4.12 ± 1.28 ng ml−1, respectively. The concentrations of progesterone were higher in pregnant cows in comparison with nonpregnant cows. CLs with a cavity in pregnant cows contained a higher volume of luteal tissue and higher secretory activity compared to homogeneous CLs.