Cervical immune activation during the luteal phase may compromise subsequent trans-cervical ram sperm transport

Abstract

Worldwide, cervical artificial insemination (AI) using frozen–thawed semen yields low pregnancy rates. The only exception to this is in Norway, where vaginal insemination with frozen–thawed semen yields pregnancy rates in excess of 60% and which has been attributed to the specific ewe breed used. Our previous work demonstrated differences in cervical gene expression at the follicular phase of the oestrous cycle in ewe breeds with known differences in pregnancy rates. In this study, we characterised the cervical transcriptome of the same ewe breeds (Suffolk, Belclare, Fur and Norwegian White Sheep (NWS)) during the luteal phase, as an optimal environment at the luteal phase could better prepare the cervix for sperm migration through the cervix at the subsequent follicular phase. High-quality-RNA extracted from post-mortem cervical tissue was analysed by RNA-sequencing. After stringent filtering, 1051, 1924 and 611 differentially expressed genes (DEGs) were detected in the low fertility Suffolk breed compared to Belclare, Fur and NWS, respectively. Gene ontology analysis identified increased humoral adaptive immune response pathways in Suffolk. Increased expression of multiple immune genes supports the presence of an active immune response in the cervix of Suffolk ewes which differentiates them significantly from the other three ewe breeds. Inflammatory pathways were up-regulated in the Suffolk, resulting in higher expression of the potent pro-inflammatory cytokines. Therefore, higher levels of pro-inflammatory cytokines indicate unresolved inflammation in the cervix of the low fertility Suffolk breed that could contribute to reduced cervical sperm transport in the next follicular phase.

Exploring Endogenous and Exogenous Factors for Successful Artificial Insemination in Sheep: A Global Overview

“…Sheep are associated with several endogenous and exogenous factors that can vary significantly between individuals and breeds, affecting the effectiveness of AI [ 5 , 6 ]. The impact of exogenous factors, such as estrus induction, synchronization [ 7 , 8 ], semen collection methods [ 9 ], and choices between fresh, chilled, or frozen semen [ 10 ], has been the subject of extensive studies in the context of ovine AI. However, it is equally important to recognize the impact of endogenous factors to the success of ovine AI programs.…”