Intrauterine growth restriction is associated with strong alterations in placental structure and function in horses

Abstract

In equids, placentation is diffuse and the nutrient supply to the fetus is determined by uterine size, which is correlated to maternal size and parity. That the size of the mare affects fetal development has previously been shown by embryo transfer (ET) between Ponies and Thoroughbreds [Allen WR, et al; Reproduction 2002;123:445-53.]. We enhanced or restricted fetal growth through ET using Pony (P), Saddlebred (S) and Draft (D) horses and investigated placental morphology, histology and function at term. Control pregnancies of P-P (n1⁄421), S-S (n1⁄428) and D-D (n1⁄48) were obtained by artificial insemination. Enhanced and restricted pregnancies were obtained by transferring P (P-D, n1⁄46) and S embryos (S-D, n1⁄48) into D mares or S embryos into P mares (S-P, n1⁄46), respectively. Placental weight and gross surface area were recorded at delivery. Samples were collected for stereology (quantitative histology) and RT-qPCR analysis of expression of genes involved in placental growth, vascularization and nutrient transport. Statistical analysis of data was performed by Kruskal-Wallis with Dunn’s posthoc test. Data are expressed as means SEM. Mean placental weight and gross surface area were higher in S-S and in D-D compared to P-P (p<0.05) whereas S-S and D-D were not different (4.6 0.17kg and 8046 176.1cm2 in S-S versus 4.9 0.41kg and 9229 596.2cm2 in D-D versus 2.5 0.14kg and 2940 111.7cm2 in P-P for placental weight and surface, respectively). No histological changes were observed among controls, but most genes had their expression decreased in P-P compared to S-S and D-D. P-D foals had a