Effect of exogenous progesterone on embryo size and ewe uterine gene expression in an ovine ‘dam size' model of maternal constraint

Abstract

Progesterone (P4), acting via its receptor, regulates uterine function and histotroph production, which are crucial to embryo growth. This study aimed to examine exogenous P4 effects on embryo size and differential endometrial gene expression at Day 19 of gestation using a 'dam size' sheep model of maternal constraint. Purebred Suffolk (S, genotypically large) embryos were transferred into recipient groups of Cheviot (C, genotypically small) or Suffolk ewes that had, or had not, been pre-treated with P4 from Days 0 to 6 of pregnancy. At Day 19S embryos were collected from four experimental groups: P4 pretreated S ewes (SP4; n=5), untreated S ewes (SnP4; n=15), P4 pretreated C ewes (CP4; n=7) and untreated C ewes (CnP4; n=21). Day-19 embryos from CP4 ewes were larger (P<0.05) than those from CnP4 ewes and similar in size (P>0.05) to embryos from SnP4 and SP4 ewes. Expression of mucin 1 (MUC1) and prostaglandin-endoperoxide synthase 2 (PTGS2) was upregulated in uterine horns ipsilateral to the corpus luteum from CP4 ewes. Prostaglandin receptor (PGR), MUC1 and PTGS2 expression was upregulated, whilst cathepsin L (CTSL) and radical S-adenosyl methionine domain-containing 2 (RSAD2) expression was downregulated in the ipsilateral horn of SP4 ewes. This suggests that pretreating ewes with exogenous P4 may alleviate early pregnancy maternal constraint via mechanisms that alter uterine function. However, further research is required to investigate the timing of P4 administration and its impact on conception rates.

Embryo development and survival in peripubertal ewe lambs

“…We observed a positive relationship between progesterone concentrations and conceptus size/development on Day 3, but not Day 14, of pregnancy. The effects of supplementary progesterone on increasing conceptus/fetal size is well documented in both sheep and cattle (Kleemann et al 1994;Mann et al 2006;Satterfield et al 2006;Fermin et al 2018aFermin et al , 2018b. Additionally, Shorten et al (2018a) showed a link between increased concentrations of progesterone in recipients and increased conceptus length when examining bovine embryos collected on Day 15 of pregnancy that had been transferred into recipients on Day 7 of pregnancy.…”

“…We observed a positive relationship between liveweight of the ewe and embryo development on Day 3 in the first year of the trial, but this was not extended to the second year or Day 14. Previous studies have shown differences in embryo size following transfer of embryos into different sheep breeds with a small or large body size, with the larger ewes having longer conceptuses on Day 19 (Sharma et al 2013;Fermin et al 2018b). Thus, increased liveweight may advance embryo development.…”