Late gestation maternal overnutrition alters gene expression and histomorphology in neonatal foal testes

Abstract

While obesity has deleterious effects on metabolism, performance, lameness, and health in mature horses, little is known about the impacts to reproductive health in foals from overfed dams. The objective of this study was to determine the effects of maternal overnutrition on neonatal foal testicular development. To test this, 16 Quarter horse mares were used in a completely randomized design and stratified by expected foaling date, body weight, and body condition score into one of two dietary treatments offered twice daily beginning on gestational d 235: control (CON; n = 8) fed to meet nutrient requirements and overfed (HIGH; n = 8) fed 40% above CON. At 5 h postpartum, foals were humanely euthanized, and testes were harvested, weighed, and stored for analyses. RNA was extracted and submitted for RNA sequencing. Histomorphometric evaluations were performed using a hematoxylin & eosin stain. ImageJ software was used to evaluate individual seminiferous tubule (ST) area, ST number, and % area of STs relative to interstitial tissue, as well as Sertoli cell numbers per ST. Data were analyzed using the MIXED procedure in SAS. Testes from HIGH male foals (n = 4) were 61% larger than testes from CON male foals (n = 4; P < 0.01). RNA sequencing revealed 56 differentially expressed genes between HIGH and CON groups (P-adjusted < 0.05). These genes represent biochemical pathways involved in oxidative phosphorylation, fatty acid metabolism, and thermogenesis, which are integral for testicular development and function. Gene ontology analyses revealed differential gene expression was associated with biological processes relevant to reproductive function and spermatogenesis, including cellular respiration and mitochondrial function. Histological analyses revealed no difference in individual ST area (P = 0.76) or Sertoli cell number within STs (P = 0.57); however, testes from CON foals had 2.3x more STs per 10X field than HIGH foals (P = 0.01) along with STs representing a greater percentage of the image area relative to interstitial tissue (P = 0.05). These data from the neonatal foal indicate that late- gestation maternal overnutrition alters fetal testicular development with potential long-term implications.