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Recent data obtained in our laboratory suggest that feeding pregnant broodmares with cereal concentrates may affect both mare and foal metabolism in the short and long term. Here, we investigated feto-placental biometry and placental function at term in mares fed with cereals and forage or forage only. Twenty-two multiparous mares inseminated with the same stallion were allocated to 1 of 2 groups from 7 months of gestation: group F (n = 10) were fed forage only, whereas group B (n = 12) received forage and cracked barley until foaling. At 3 and 9 months of gestation, a glucose tolerance test (IVGTT) was performed to evaluate the insulin resistance of pregnant mares. At birth, placentas and foals were weighed and measured. Placental samples were collected above the umbilical cord insertion and snap frozen. An RNA sequencing (RNAseq) analysis was performed on 9 placentas of each group. After normalization, gene levels were analysed using the DESEqn 2 package of R software (https://www.r-project.org/). Enrichment of gene sets was analysed using the Gene Set Enrichment Analysis (GSEA) software using the Kyoto Encyclopaedia of Genes and Genomes (KEGG) and Gene Ontology [GO, biological processes (bp), molecular function (mf) and cellular components (cc)] databases. Gene analysis statistical results were considered significant for P-values

Modifications of maternal environment could alter fetal growth and development through the placenta and thus health in adulthood. The developmental origins of health and disease suggest that maternal nutrition during pregnancy may affect offspring development and subsequent energy metabolism. To understand the effect of common feeding practices during gestation, 24 saddlebred mares were allocated to 1 of 2 groups: group B was supplemented twice a day with barley (B) and group F was fed only with fodder (F) between month 7 of gestation and foaling. B mares maintained an optimal body condition score through gestation, with an increase in glycaemia and insulinemia after each meal and insulin resistance in month 9 of gestation. F mares lost condition as assessed by body condition score in the last part of gestation, leading to a moderate undernutrition and a transitional increase in nonesterified fatty acid plasma concentrations. Diets had no effect on feto-placental biometry or on placental structure. In contrast, an increase in microcotyledonary vessel volume was observed in F placentas, indicating placental adaptation, possibly to increase fetomaternal exchanges. There was no overall difference in the expression of genes involved in vascularization, nutrient transfer, growth, and development between placentas from B and F mares. Nevertheless, as seen in other species, sex-specific effects of maternal nutrition were observed in placentas from female foals, with differences in the expression of endogline, kinase insert domain receptor, insulin-like growth factor 2 and insulin-like growth factor 1 receptor genes. This study demonstrates that breeding practices such as supplementation in concentrate at mid-gestation do not seem to affect fetal development. More work is ongoing to evaluate postnatal health.

In equids, placentation is diffuse and the nutrient supply to the fetus is determined by uterine size, which is correlated with maternal size. The size of the mare affects fetal development as shown by embryo transfer (ET) between Ponies and Thoroughbreds. In turn, insulin sensitivity in the newborn foal and subsequent postnatal growth rate are affected. We enhanced or restricted fetal growth through ET using Pony (P), Saddlebred (S), and Draft (D) horses and investigated placental morphology, structure, and function at term. Control pregnancies of P-P (n = 21), S-S (n = 28), and D-D (n = 8) were obtained by AI. Enhanced and restricted pregnancies were obtained by transferring P (P-D, n = 6) and S embryos (S-D, n = 8) into D mares or S embryos into P mares (S-P, n = 6), respectively. Placental weight and surface were recorded at delivery. Samples were collected for stereology and RT-qPCR analysis of expression of genes involved in placental growth, vascularization, and nutrient transport. Housekeeping genes were RPL32, SCAMP3, and B2M. Data were analysed by Kruskal-Wallis followed by Dunn's post hoc test. Placental weight and surface were increased in S-S and in D-D compared with P-P, whereas S-S and D-D were not different. No histological changes were observed among controls, but most genes had their expression decreased in P-P compared with S-S and D-D. The P-D foals had a 57% increased birthweight with heavier and larger placentas than P-P foals. The S-D foals were similar to both S-S and D-D in terms of birthweight and placental weight and surface. No major modifications in placental histology or transcript levels were observed in both enhanced groups. In contrast, S-P foals had a 37% decreased birthweight with lighter and smaller placentas compared with S-S and S-D foals. There was no gross histological difference between S-P and S-S but the microcotyledonary surface density was higher in S-P compared with S-D. Moreover, the expression of IGF2, IGF2R, SLC2A1, and eNOS was decreased in S-P compared with S-S. There was no difference in gene expression between S-P and P-P. In conclusion, intrauterine growth restriction led to marked changes in placental morphology, histology, and gene expression. The increased microcotyledonary surface density suggests a lengthening of villi, which could increase feto-maternal contact surface as a compensatory mechanism for the restricted uterine capacity. Surprisingly, placental adaptation to the restricted intrauterine environment in S-P induced gene profiles resembling that of control P, whereas no difference was observed in enhanced pregnancies.

In equids, the size of the uterus determines fetal intrauterine development, which in turn affects postnatal insulin sensitivity and growth rate. We induced intrauterine growth enhancement through embryo transfer using Pony (P), Saddlebred (S), and Draft (D) horses and studied growth and insulin sensitivity in foals from birth to one year of age. Control pregnancies of S-in-S (n = 14) and P-in-P (n = 10) were obtained by AI. Enhanced fetal growth was obtained by transferring S (S-in-D, n = 7) and P embryos (P-in-D, n = 5) into D mares. From birth to weaning (180 days), each foal was kept with its surrogate P, S, or D dam. At 3, 140, and 380 days, glucose clearance and pancreatic beta cell response to exogenous glucose were assessed with an intravenous glucose tolerance test (IVGTT). At 200 days, the euglycemic-hyperinsulinemic clamp method was used to determine the sensitivity and responsiveness of tissues to exogenous insulin. Plasma T3, T4, and IGF1 were assayed at 3 and 180 days. Data were analysed using one-way ANOVA and Tukey post hoc tests. S-in-S were heavier and taller than P-in-P from birth to 380 days (P