Relationship between ultrasonic characteristics of the corpus luteum, plasma progesterone concentration and early pregnancy diagnosis in Friesian mares

The purpose of the present study was to evaluate the change in cross-sectio nal area of the early corpus luteum (CL) and progesterone production in rel ation to subsequent pregnancy diagnosis. The cross-sectional area of the CL of 75 Friesian brood mares was measured by ultrasonography on Day 1 or 2 a nd Day 8 or 9 after ovulation. The change in cross-sectional area was expre ssed in a volume ratio. Plasma progesterone concentrations were measured on Days 8 to 9, and ultrasonography to determine pregnancy status was carried out on Day 17. The data obtained were analyzed by using a multiple logisti c regression model. There were significant differences in the age, volume ratio and progesteron e concentration between pregnant and nonpregnant mares Pregnancy on Day 17 was related to the change in size of the CL up to Days 8 to 9 and progester one concentration on Days 8 to 9. These differences between pregnant and no npregnant mares might reflect the first luteal response to pregnancy. (C) 1 999 by Elsevier Science Inc.