133 COMPARISON OF ENDOMETRIAL TRANSCRIPTOME CHANGES BETWEEN IPSI- AND CONTRALATERAL HORNS DURING DIESTROUS AND ITS RELATIONSHIP WITH THE ABILITY TO SUPPORT CONCEPTUS ELONGATION IN CATTLE

Data from embryo transfer studies indicate that transfer to the uterine horn contralateral to the ovary containing the corpus luteum (CL) reduces pregnancy rate. The aim of this study was to compare the ipsi- v. contralateral horns in terms of (1) endometrial gene expression and (2) the ability to support conceptus growth to Day 14. In Experiment 1, endometrial samples from the ipsi- and contralateral horns were collected from synchronized nonpregnant heifers slaughtered on Day 5, 7, 13 or 16 post-oestrus (n = 5 per time point) and snap frozen for subsequent analysis. In Experiment 2, fresh Day 7 in vitro-produced blastocysts were transferred to the uterine horn(s) ipsilateral (Group I, n = 9 recipients) or contralateral to the CL (Group C, n = 8) or to both horns (i.e. bilateral, Group B, n = 9) of synchronized recipients (10 embryos transferred per horn per recipient). All recipients were slaughtered on Day 14. Reproductive tracts were recovered and each horn was flushed independently. The number and dimensions (length and width) of recovered conceptuses were recorded independently for each horn. Embryo data were analysed using PROC MIXED in SAS (SAS Institute Inc., Cary, NC, USA). The model had treatment as a fixed effect and heifer within treatment as a random effect. Experiment 1, RNA-Seq analysis of endometrium, detected 217, 54, 14, and 18 differentially expressed genes (>2-fold change, false discovery rate P   0.05). Thus, significant differences in endometrial gene expression exist between the uterine horns ipsi- and contralateral to the CL in cattle, but those differences do not affect conceptus elongation on Day 14. Research was supported by Science Foundation Ireland (13/IA/1983) and the Irish Department of Agriculture, Food and The Marine (13S528).