Blood perfusion and diameter of bovine corpus luteum as predictors of luteal function in early pregnancy.

A feasible and non-invasive luteal function assessment which enables timely intervention to improve progesterone (P4) support at early pregnancy is not well-established. The aim of this study was to determine the correlation among morphological and functional assessment methods of corpus luteum (CL) on Day 5 (D5) following timed-artificial insemination effect on luteal blood perfusion (LBP), CL diameter and serum P4 concentration. Beef heifers (n = 89) were synchronized and inseminated (D0). On D5, CL was scanned by colour-Doppler ultrasonography using an LBP score (0 = absent; 3 = high blood perfusion); CL diameter was obtained and blood was collected. Diameter of CL had a positive linear effect on P4 concentration (p < .001); and larger CL diameter increased the probability to become pregnant (p < .05; odds ratio =1.21). Heifers with a CL larger than 14.95 mm had a higher pregnancy rate than heifers with a 14.95 mm or smaller CL (p < .05). Animals with LBP 2 and 3 had larger CL when compared to scores 0 and 1 (p < .001). Scores 1, 2 and 3 can accurately estimate heifers with higher P4 (accuracy =0.79, 0.72 and 0.61 respectively). In conclusion, LBP on Day 5 post-TAI allows to estimate heifers with higher P4 and larger CL size, and a larger CL diameter was positively associated with pregnancy rate.