Inflammation: friend or foe of bovine reproduction?

Sylvie Chastant,Marie Saint-Dizier

doi:10.21451/1984-3143-ar2019-0057

Abstract

Inflammation is not only the first line of defense of the organism but is also required in many reproductive processes such as ovulation, corpus luteum development, luteolysis, uterine clearance after insemination and post partum. Nevertheless, if excessive or persistent, inflammation can switch from a positive mechanism to a deleterious process, impairing oocyte quality and embryo development. Not only uterine but also non genital inflammatory sites can depreciate reproductive performances, with a carry over effect of 2 to 4 months. Since the metabolic challenges of the peripartum transition period make difficult for the cow to control inflammation, dairy cows are frequently in a pro-inflammatory stage, suggesting that inflammation, rather than infection, is a limiting factor of fertility in modern dairy cows. Within the first week after calving, cows have to mount an intense inflammatory response to the bacterial invasion of the uterine cavity with the challenge of being able to switch it off in no more than 5-6 weeks. The absence of neutrophils on endometrial smear is associated with the highest success rate at insemination. Since a fine tuning – rather than an absence - of inflammation is required along the reproductive cycle, anti-inflammatory drugs do not allow any improvement of pregnancy rate, except in the specific case of embryo transfer. Appropriate management of the transition period (especially nutritional) and in a long term perspective, genetic selection contribute to improve the aptitude of cows to controls the intensity of inflammatory process.

Highlights

Inflammation is the first line of defense of the organism but is required in many reproductive processes such as ovulation, corpus luteum development, luteolysis, uterine clearance after insemination and post partum
The objective of this paper is to review the positive and negative relationships between inflammation and cow reproduction, to question the rationale of the use of anti-inflammatory drugs to improve reproductive performances
The tendency to an overactivity of proinflammatory systems and the instability of inflammation control in post partum dairy cows are pictured in endometrial smears follow-up: even when cows solved their uterine inflammation at 40-45 days post partum (0% PMN), transient episodes of reactivation of the uterine inflammation were observed after 60 days post partum

Summary

Introduction

Inflammation is the first line of defense of the organism but is required in many reproductive processes such as ovulation, corpus luteum development, luteolysis, uterine clearance after insemination and post partum. Transmembrane toll-like receptors (TLRs) are probably the most classical PRRs and are expressed by bovine granulosa cells (Price and Sheldon, 2013), bovine oviductal epithelial cells, epithelial and stromal cells of the endometrium (Herath et al, 2009; Turner et al, 2014; Dadarwal et al, 2017; Danesh Mesgaran et al, 2018). These different compartments are able to mount an early immune response: recognition of MAMPs or DAMPs by the genital cells initiate several signaling cascades (through NFκB or MAPkinase pathways for example), resulting in the expression of pro-inflammatory mediators (e.g. Tumor Necrosis Factor α -TNFα-, interleukin- IL 1 and 8), Chastant and Saint-Dizier. Pro-inflammatory cytokines induce important microcirculatory events, at short (vasodilation) and long term (neoangiogenesis contributing to tissue healing)

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Conclusion