63 Impact of Endometrial Biopsy on Corpus Luteum Function

Abstract

Reproductive procedures involving uterine manipulation (UM), such as transcervical embryo transfer (TET) or the collection of an endometrial biopsy (EB) may cause trauma to the endometrium resulting in release of endogenous prostaglandin F_2α (PGF_2α) causing premature regression of the corpus luteum (CL). This study aimed to evaluate the effect of UM and EB on corpus luteum lifespan in tropically adapted beef heifers. In Experiment 1, pre-synchronised Droughtmaster heifers (n = 9; 25.8 ± 0.4 m, live weight 391 ± 21.5 kg) were randomly selected either at Day 4 (UM4 = 5) or at Day 7 (UM7 = 4) post-oestrus for transrectal uterine manipulation and transcervical passage of the biopsy Storz® device without sample collection. In Experiment 2, pre-synchronised Charbray heifers (n = 13, 2 to 3 years old, live weight 439.8 ± 17.2) were biopsied in the horn ipsilateral to the CL at Day 4 (B4 = 6) or at Day 7 (B7 = 7) post-oestrus. In both experiments, blood samples were taken from jugular/coccygeal vein throughout the oestrus cycle on Days 3, 4, 6, 7, 9, 11, 13, 16 and 19 (Day 0 = synchronised oestrous) for progesterone (P4) analysis. Signs of heat were visually detected daily and confirmed by ovarian ultrasound. For the PGF_2α metabolite 13,14-dihydro-15-keto-PGF_2α (PGFM) assessment, blood samples were collected before and after uterine trauma at –24, –12, 0 h and +6, +18, +24 h (Hour 0 = UM or EB either at Day 4 or Day 7). Progesterone was assessed by liquid chromatography-mass spectrometry (LC-MS) and PGFM using an enzyme immunoassay DetectX® kit (Arbor Assays, Ann Arbor, MI, USA). The intra- and interassay coefficients of variations were 3.7% and 12.8%, respectively. A series of generalized additive mixed effect models (GAMM) were created to quantify P4 differences for UM and EB. The results showed that oestrous cycle length was not affected by UM or EB conducted at Day 4 or at Day 7, because P4 concentration remained above 1 ng mL⁻¹ after uterine trauma during dioestrus. Also, UM and EB did not induce the release of luteolytic pulses of PGF_2α. Although P4 concentration followed the normal cycling pattern throughout the oestrus cycle, the shape of the curve in EB4 and UM4 heifers showed higher concentrations of P4 compared with EB7 and UM7 heifers. In conclusion, UM and EB with Storz® device during metoestrus or early dioestrus had minimal or nil effects on CL activity. Whether lower P4 profiles affect embryo development after uterine trauma needs to be further elucidated.