Collagen and Microvascularization in Placentas From Young and Older Mares

Abstract

In older mares, increasing collagen fibers (fibrosis) in the endometrium and oviduct predisposes to sub-fertility and infertility. In this study, (i) gene transcription of collagen (qPCR: COL1A1, COL1A2, COL3A1, COL5A1); (ii) total collagen protein (hydroxyproline); (iii) collagen distribution (Picrosirius red staining; polarized light microscopy); and (iv) microvascular density (Periodic acid-Schiff staining), were evaluated in mares' placenta, and related to mares age, and placenta and neonate weights. Samples were collected from the gravid horn, non-gravid horn, and body of the placenta from younger (n = 7), and older mares (n = 9) of different breeds. Transcripts of COL1A1, COL3A1 and COL5A1, total collagen protein, chorionic plate connective tissue thickness, and microvascularization increased in the gravid horn of older mares' placentas, compared to the youngest (P < 0.05). Although in other species placenta fibrosis may indicate placental insufficiency and reduced neonate weight, this was not observed here. It appears that older fertile mares, with more parities, may develop a heavier, more vascularized functional placenta with more collagen, throughout a longer gestation, which enables the delivery of heavier foals. Thus, these features might represent morphological and physiological adaptations of older fertile mares' placentas to provide the appropriate nutrition to the equine fetus.

Evolution of the Concepts of Endometrosis, Post Breeding Endometritis, and Susceptibility of Mares

“…Since equine conceptus development relies initially on the nutrients that derive from exocrine secretions of endometrial glands (histotroph), and later on the placenta, endometrium and placenta's health are intertwined [83]. A study was carried out in the laboratory of Ferreira-Dias and her group to evaluate COL in placenta from young and older mares [84]. Although COL increased in the pregnant horn of the placenta of mares between 10 and 15 years of age, it did not appear to impair fertility [84].…”

“…A study was carried out in the laboratory of Ferreira-Dias and her group to evaluate COL in placenta from young and older mares [84]. Although COL increased in the pregnant horn of the placenta of mares between 10 and 15 years of age, it did not appear to impair fertility [84]. However, in this study the maximum age of the mares was 15 years, the age after which mares are more likely to develop endometrosis, placental malfunction, and placenta with histopathological lesions related to infertility [36,85].…”

Collagen Type III as a Possible Blood Biomarker of Fibrosis in Equine Endometrium

“…Due to the highly restricted distribution of hydroxyproline in collagen and elastin, the hydroxyproline content generally reflects the amount of collagen in samples. Therefore, since quantification of hydroxyproline has been utilized for evaluating tissue fibrosis or collagen deposition [ 34 , 35 , 36 ], it was used in this study. As the degree of endometrosis in mares increases with age [ 3 , 5 , 6 ], the age effect was also studied.…”