How early can nonpregnant ewes be detected based on the blood flow of the corpus luteum?

The study aimed to characterize morpho-functional changes in corpus luteum (CL) in pregnant and non-pregnant sheep, propose diagnostic criteria for non-pregnancy, and assess diagnostic accuracy around the expected luteolysis period. Crossbred ewes (n = 34) underwent estrous synchronization, divided into G1 (unmated, n = 20) and G2 (mated, n = 14). The day of ovulation was considered as day 0 (D0). Luteal dynamic was monitored from D0 to D17, with blood samples collected every 72 h for progesterone (P4). Pregnancy was definitively diagnosed at day 30. Analyses included CL area (CLA), CL blood flow (CLBF), CLBF:CLA ratio, and serum P4. Statistical models considered group, day, and interactions. Accuracy for early pregnancy diagnosis (days 12–17) was assessed. CLBF:CLA ratio (14.3 ± 8.1 vs. 20.3 ± 10.7; 10.2 ± 10.4 vs. 17.8 ± 9.4; 1.3 ± 4.1 vs. 16.0 ± 8.2%), CLBF (0.41 ± 0.3 vs. 0.49 ± 0.3; 0.26 ± 0.3 vs. 0.45 ± 0.3; 0.06 ± 0.2 vs. 0.34 ± 0.2 cm2), and CLA (2.5 ± 1.1 vs. 2.3 ± 0.9; 1.9 ± 1.1 vs. 2.3 ± 1.1; 0.9 ± 1.2 vs. 2.0 ± 1.2 cm2) differed (P 90% from day 15 on for CLBF and CLBF:CLA ratio, but not for CLA. At this day, CLBF and CLBF:CLA ratio were circa 50-fold greater in pregnant than in nonpregnant ewes (p