Wilsher S, Allen W R
University of Cambridge, Department of Clinical Veterinary Medicine Equine Fertility Unit, Mertoun Paddocks, Woodditton Road, Newmarket, Suffolk CB8 9BH, UK.
Equine Vet J. 2003 Jul;35(5):476-83. doi: 10.2746/042516403775600550.
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.
Degenerative changes in the endometrium with increasing age and parity are reflected in the morphology and density of the placental microcotyledons.
To assess placental efficiency on the basis of foal birthweight as a function of total microscopic area of fetomaternal contact.
Stereology was used to examine the placentae of 84 Thoroughbred 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.
Mare age and parity influenced the development of the microcotyledons and microcotyledon surface density (Sv) was lowest in aged multiparous mares, presumably due to degenerative changes in their endometrium. However, primiparous mares also showed significantly lower Sv values than young multiparous mares, despite the virginal endometrium of the former group. This apparent 'priming' effect of a first pregnancy on microcotyledonary Sv was illustrated further by 11 maiden mares followed in 2 successive pregnancies. They all showed significant increases in Sv values in their second parity, with equivalent improvements in foal birthweight.
Foal birthweight 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.
Further work is needed to elucidate how such changes in microcotyledon morphology and efficiency are brought about.
马胎盘的正常状态对胎儿健康和发育至关重要。关于胎盘大体形态学状况已有大量信息，但很少有研究探讨干扰胎盘形态和胎盘效率的退行性病变问题。
随着年龄和胎次增加，子宫内膜的退行性变化反映在胎盘微叶的形态和密度上。
根据驹出生体重作为母胎接触总面积的函数来评估胎盘效率。
采用体视学方法检查84匹纯种母马的胎盘，这些母马按年龄和胎次分组。还测定了胎盘效率，通过将驹出生体重表示为母胎接触总面积的函数来评估。
母马年龄和胎次影响微叶的发育，老龄经产母马的微叶表面密度（Sv）最低，推测是由于其子宫内膜的退行性变化。然而，初产母马的Sv值也显著低于年轻经产母马，尽管前一组母马的子宫内膜为处女型。11匹未孕母马连续两次妊娠的情况进一步说明了首次妊娠对微叶Sv的这种明显“启动”效应。它们在第二胎时Sv值均显著增加，驹出生体重也有相应改善。
驹出生体重反映了母胎接触与胎盘效率之间的平衡。母胎接触增加与胎盘效率降低相关，这可能反映了胎盘改变其交换能力的能力。
需要进一步研究以阐明微叶形态和效率的这种变化是如何发生的。
