Effects of obesity and hyperleptinemia on progesterone, equine chorionic gonadotropin, and fetal biometry during the first 70 days of pregnancy

Abstract

While consequences of equine obesity are well defined, the extent to which persistent hyperleptinemia (HL) affects the fetal-maternal environment warrants further exploration as HL and often accompanying leptin (Lep) resistance have been shown to perturb processes such as angiogenesis in the developing placentae of other species. Therefore, this study aims to compare endocrine, fetal, placental, and uterine factors during the first 70 d of pregnancy of mares with persistent HL versus mares with normal Lep (NL) concentrations. Plasma Lep and body condition scores (BCS; 1–9) were determined throughout the year to confirm persistent HL and obesity. Percentile-based cutoffs were used to divide mares into 2 groups. Fourteen resident mares were identified as either HL (n = 8; mean Lep 8.6 ng/mL ± 0.8; BCS 7.5; median age 15) or NL (n = 6; mean Lep 1.2 ng/mL ± 0.2; BCS 5.3; median age 16). Before breeding, plasma Lep was greater (P < 0.0001), and BCS was higher (P < 0.01) in mares with HL compared with NL-mares based on t-tests. Mares were artificially inseminated with at least 500 × 10⁶ progressively motile sperm from one proven stallion upon detection of a follicle ≥35 mm and uterine edema. Ovulation was induced with 2500 IU hCG and blood samples were collected for 6 successive days starting on the day of ovulation. Additional blood sampling occurred on d 12 and 25 and every 10 d thereafter until d 70 to characterize progesterone and eCG. Embryonic vesicle diameter was recorded on d 14 and 25. On d 70, fetuses were collected transcervically, and crown-rump length, fetal weight, and placental weight were determined. Placental and endometrial tissues were frozen for later analyses. Two-way ANOVA and t-tests were used to compare progesterone over time and eCG and fetal growth parameters, respectively. No differences were observed in vesicle diameter on d 14 or 25. Plasma progesterone increased after ovulation and was greater (P < 0.001) in HL-mares on d 70. Concentrations of eCG were first detected on d 45 and remained elevated until d 70; however, no differences were found between groups. Crown-rump length, and fetal and placental membrane weights did not differ between the groups. Ongoing analyses aim to compare the transcriptome of fetal and maternal tissues between mares with HL and NL. In this study, pre-existing obesity and HL did not alter fetal biometry within the first 70 d of pregnancy, nor did they alter eCG secretion into peripheral circulation. Plasma progesterone did appear to diverge on d 70; however, further sampling would be required to determine if the divergence continues thereafter.