Placental alterations in structure and function in intra-uterine growth-retarded horses.

The research investigates the effects of embryo transfer (ET) on the placenta of horses, with particular focus on the influence of the breed and size of the recipient mare on fetal development, postnatal growth rate, and insulin sensitivity in foals. The researchers found that placental structure and gene expression are modified after ET into a smaller or larger breed than that of the embryo, leading to either restricted or enhanced foal growth.

Research Methods

This in vivo study analyses the placental adaptation in pregnancies where increased or restricted fetal growth was induced via ET between Pony, Saddlebred, and Draught horses. Here’s how the researchers proceeded:

• Artificial insemination was used to obtain control Pony (P, n = 21) and Saddlebred (S, n = 28) pregnancies.
• In order to induce increased fetal growth, Pony (P-D, n = 6) and Saddlebred (S-D, n = 8) embryos were transferred into Draught mares.
• Restricted growth pregnancies were obtained by transferring Saddlebred embryos into Pony mares (S-P, n = 6).
• Data was collected on placental weight, surface, and stereologic characteristics, as well as gene expressions relevant to placental growth, vascularization, and nutrient transport.
• Data was then analysed using a linear model.

Results

The researchers noted the following outcomes:

• Foals that resulted from Saddlebred embryos transferred into Pony mares (S-P) were growth-restricted compared to controls. This happened despite their having increased gestational length.
• The placental weight in such foals (S-P) was reduced, but the surface density and volume fraction of the placenta increased.
• The expression of genes involved in placental growth, development, and nutrient transfer was markedly reduced in these foals (S-P).
• Conversely, placental size and weight increased in foals resulting from Pony and Saddlebred embryos placed in Draught mares (P-D and S-D).
• In these enhanced-growth foals (P-D and S-D), the density of the trophoblastic surface and the allantoic vessels surface decreased, with few modifications noted in gene expression.

Conclusions

The research concludes that control embryos produced by artificial insemination differ significantly in placental structure and gene expression from those produced by ET into a smaller or larger breed than that of the embryo. These adaptations play a pivotal role in the observed phenotypes of foal growth restriction or enhanced growth at birth.