The effects of maternal age and parity on placental and fetal development in the mare

Abstract

Reasons for performing study: The normality of equine placentation is essential for fetal health and development. Substantial information exists on the gross morphological status of the placenta but few studies have addressed the problem of degenerative lesions that interfere with placental morphology and placental efficiency. Hypothesis: Degenerative changes in the endometrium with increasing age and parity are reflected in the morphology and density of the placental microcotyledons. Objective: To assess placental efficiency on the basis of foal b i rthweight as a function of total microscopic area of fetomaternal contact. Methods: Stereology was used to examine the placentae of 84Thoroughbred mares grouped on the basis of age and parity. Placental efficiency, assessed by expressing foal birthweight as a function of total microscopic area of fetomaternal contact, was also determined. Results: Mare age and parity influenced the development of the microcotyledons and microcotyledon surface density (S v ) was lowest in aged multiparous mares, presumably due to degenerative changes in their endometrium. However, primiparous mares also showed significantly lower S v values than young multiparous mares, despite the virginal endometrium of the former group. This apparent 'priming' effect of a first pregnancy on microcotyledonary S v was illustrated furt h e r by 11 maiden mares followed in 2 successive pregnancies. They all showed significant increases in S v values in their second parity, with equivalent improvements in foal birthweight. Conclusions: Foal birthweight is a reflection of the balance between fetomaternal contact and placental eff i c i e n c y. I n c reases in fetomaternal contact are correlated to reductions in placental efficiency, which may reflect the ability of the placenta to modify its exchange capabilities. Potential relevance: Further work is needed to elucidate how such changes in microcotyledon morphology and efficiency are brought about.

Gestational length in Carthusian broodmares: effects of breeding season, foal gender, age of mare, year of parturition, parity and sire

“…Moreover, foal birth weight is a reflection of the balance between fetomaternal contact and placental efficiency. Increases in fetomaternal contact are correlated to reductions in placental efficiency, which may reflect the ability of the placenta to modify its exchange capabilities and hence its influence upon fetal growth (Wilsher and Allen 2003). Furthermore, it has been postulated that the difference in foal gender is due to different endocrine functions of the fetus, interacting differently with the control of parturition (Jainudeen and Hafez 2000).…”

“…Younger animals, particularly if they are around 4-5 year-olds might not be completely developed yet, as the growth rate of Carthusian and Andalusian horses is slower than in other equine breeds. On the other hand, mares older than 13-14 years usually require more mating per conception, which is explained by progressive degenerative changes in the endometrium and increased susceptibility to infections (Pashan and Allen 1979, Rossdale et al 1992, Wilsher and Allen 2003, Gluckman and Hanson 2004. The degenerative changes in the endometrium might potentially reduce its nutritive capacity for the development of the fetus (Satué 2004).…”

Dysregulation of methylation and expression of imprinted genes in oocytes and reproductive tissues in mice of advanced maternal age

“…*, P<0.05 recovery from mice 6-8 weeks old was 39.5±7.4 oocytes compared to 4.4±3.6 oocytes from mice aged 16 months [30]. Fetal growth restriction is also associated with advanced maternal age in women [3,22,23] and mares [24], and there is a higher incidence of embryonic loss and miscarriage in older women [2][3][4]12] and mares [8,11], consistent with the increased number of degenerating implantation sites in aged mice observed in this experiment. Also in agreement with our findings, maternal age in women is associated with abnormal placental growth; women of advanced maternal age have increased placental weights compared to younger women [39].…”

“…There is a potential link between maternal age and imprinting disorders, such as Angelman syndrome and Beckwith-Wiedermann syndrome, as these disorders are more prevalent in the offspring from older women [20,21]. Furthermore, maternal age has been associated with developmental abnormalities, including low birth weight in women [3,22,23] and mares [24].…”

Eficiência placentária na espécie equina: quais fatores podem estar relacionados?

“…A paridade parece ser mais importante para determinar o peso ao nascer do que a idade materna, isso devido à redução da densidade microcotiledonária juntamente com a redução do volume do córion, diminuindo assim a área válida para trocas hemotrófi-cas de nutrientes e gases (WILSHER; ALLEN, 2000).…”