ENDOMETRIAL VASCULAR PERFUSION DURING EARLY PREGNANCY IN HEIFERS ASSESSED BY COLOR-DOPPLER ULTRASONOGRAPHY

Abstract

Conceptus-mediated endometrial vascular changes in mares are transiently higher in the horn containing the embryo during the embryo mobility phase and remain higher in the embryo-containing horn than in the opposite horn after fixation. It was hypothesized in this study that endometrial vascular perfusion during early gestation in heifers is also conceptus-mediated. Heifers were inseminated and data collected until Day 60 (Day 0 = ovulation) in pregnant heifers or until the second ovulation in nonpregnant heifers. Endometrial perfusion was subjectively evaluated by color-Doppler scanning of each uterine horn (scored 1–4; none to maximal, respectively). Blood samples were collected daily for progesterone (P4) and estradiol (E2) assay. Heifers were retrospectively assigned to pregnant (n = 11) or nonpregnant (n = 6) groups after pregnancy diagnosis on Day 25, and horns ipsilateral and contralateral to the corpus luteum were compared. The data were partitioned for Days 0 to 18 so retrospective comparisons could be made between pregnant and nonpregnant status. Endometrial perfusion scores were not different (P>0.05) between uterine horns within each group until Day 18, so data were combined for the two horns for group comparisons. There was an increase (P<0.001) in endometrial perfusion scores in nonpregnant heifers between Days 14 to 18 that was temporally associated with the preovulatory rise in estradiol. When data from the nonpregnant group were normalized to the day of second ovulation, the increase in endometrial perfusion scores was first detected between Days -4 to -1. Plasma P4 decreased sharply between Day -4 and -3 and plasma E2 increased sharply between Day -5 and -4. There was no evidence for a similar increase in endometrial perfusion scores in pregnant heifers at this time. In the pregnant heifers, endometrial perfusion scores were compared between ipsilateral and contralateral horns from Days 0 to 60. Increased endometrial perfusion scores in the ipsilateral horn were detected between Days 18 and 20, and continued to increase until Day 40. Perfusion scores of the contralateral horn remained low until Day 32, when they began to rise, reaching perfusion scores approximately similar to the ipsilateral horn around Day 40, then declining until Day 60. In summary, an increase in endometrial vascular perfusion in nonpregnant heifers was temporally associated with decreased P4 concentrations and increased E2 concentrations. In contrast, increased endometrial perfusion scores were detected later, around Day 20, in pregnant heifers only in the horn ipsilateral to the corpus luteum and conceptus, and without temporal association with increased E2 or decreased P4. The hypothesis that an increase in endometrial vascular perfusion is conceptus-mediated in heifers was supported. These findings suggest different pathways of endometrial vascular perfusion stimulation in pregnant and nonpregnant heifers. (LAS: Supported by CAPES/Brazil scholarship.) (poster)