Immunology of infective preterm delivery in the mare.
Authors: Lyle S K
Journal: Equine veterinary journal
Summary
# Editorial Summary: Immunology of Infective Preterm Delivery in the Mare Placentitis accounts for between 10 and 34% of equine reproductive losses, with bacterial infection—particularly *Streptococcus equi* subspecies *zooepidemicus*—driving more than half of these cases. Lyle's 2014 review synthesises current understanding of how bacterial placentitis triggers premature delivery through three interconnected pathological mechanisms: direct stimulation of uterine contractions, local and systemic inflammatory signalling, and activation of the fetal hypothalamic-pituitary-adrenal axis via proinflammatory cytokine cascades. The evidence demonstrates that infectious placentitis initiates a complex immunological cascade rather than simple mechanical placental failure, with cytokine-mediated signalling being a critical driver of both myometrial activation and fetal stress responses that precipitate preterm labour. For practitioners managing mares presenting with prepartum udder development, premature lactation or vaginal discharge, understanding that bacterial placentitis engages these specific immunological pathways has direct implications for therapeutic timing and selection—suggesting that broad-spectrum antimicrobial coverage alone may be insufficient without addressing the underlying inflammatory signalling mechanisms. This mechanistic insight underscores why early detection and aggressive treatment protocols targeting both infection and inflammatory response remain essential to improving outcomes in infectious preterm delivery cases.
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Practical Takeaways
- •Recognize clinical signs of placentitis (vaginal discharge, udder development, premature lactation, delivery of premature/dead foals) as indicators requiring immediate intervention to prevent preterm loss
- •Understanding inflammatory mechanisms in equine placentitis can guide therapeutic targeting of myometrial contraction and cytokine-mediated fetal stress responses
- •Bacterial placentitis, particularly streptococcal infections, represents a significant and manageable cause of pregnancy loss that warrants investigation and prevention strategies
Key Findings
- •Placentitis accounts for 9.8-33.5% of equine abortions, stillbirths and perinatal losses
- •Bacterial infections cause 53% of placentitis cases, with Streptococcus equi ssp. zooepidemicus isolated in 28% of bacterial cases
- •Proinflammatory cytokine signalling activates the fetal hypothalamic-pituitary-adrenal axis, contributing to preterm delivery
- •Loss of myometrial quiescence secondary to inflammatory signalling is a major pathogenic mechanism in infectious preterm delivery