Effect of lactation on conceptus-maternal interactions at the initiation of implantation in cattle: Effects on the conceptus transcriptome

The hypothesis tested was that the uterine environment of lactating cows would affect conceptus gene expression. Approximately 65-75 days post-partum (dpp) the estrous cycles of non-lactating (dried off immediately post partum: n=12) and lactating (n=13) cows were synchronized and on Day 7 a high quality blastocyst derived from superovulated heifers was transferred. A control group of maiden heifers (n=8) were synchronized, inseminated to a standing heat and slaughtered on the same day as non-lactating and lactating recipients (Day 19; estrus=Day 0). The ipsilateral uterine horn was flushed with 10 ml PBS and the conceptus, when present, and uterine luminal fluid (ULF) snap frozen in liquid nitrogen prior to analysis. Gene expression analysis of the conceptus was performed by RNA sequencing analysis while amino acid (aa) composition of ULF was determined by High Performance Liquid Chromatography (HPLC). Eight differentially expressed genes (DEGs) were identified between conceptuses recovered from non-lactating cows versus heifers while 269 DEGs (100 up-regulated and 169 down-regulated) were identified between conceptuses recovered from lactating cows compared to heifers. The aa, alanine, glycine, serine and threonine, arginine, leucine and valine, were significantly lower in abundance in ULF recovered from heifers compared to both non-lactating or lactating cows. Glutamic acid, glutamine and lysine concentrations were lowest in heifers compared to both cow groups. This study demonstrates that exposure of a grade one embryo to a uterine environment that has been exposed to the metabolic stresses associated with lactation modifies the transcriptome of the conceptus and aa composition of the ULF. Overall design: Comparison of differences in mRNA in bovine conceptuses recovered from the uterus of dry and lactating dairy cows on Day 19 following embryo transfer of blastocysts from maiden heifers on Day 7 along with Day 19 conceptuses recovered from maiden heifers following AI.