Insulin sensitivity decreases during pregnancy, presumably an adaptation ensuring sufficient glucose supply to feto-placental tissues. Feeds high in non-structural carbohydrates are also linked to diminished insulin sensitivity in horses. Because the equine fetus is highly glucose reliant, maternal glucose and insulin dynamics during pregnancy may have implications for optimal fetal development in horses. Mismanagement of maternal nutrition during gestation could predispose the offspring to metabolic disorders (e.g. insulin resistance) later in life. In horses, insulin resistance is associated with increased risk for development of laminitis. These studies measured insulin sensitivity and glucose dynamics in pregnant and non-pregnant mares fed high sugar and starch (SS) or high fat and fiber (FF) feeds, as well as neonatal foals born from pregnant mares fed SS and FF feed. Insulin modified frequently sampled intravenous glucose tolerance tests (FSIGT) were applied to pregnant Thoroughbred mares (n = 22) at 28 ± 3 wks (Period 1) and 47 wks (Period 2) gestation, as well as non-pregnant mares (n=10) measured simultaneously. Following the first FSIGT mares were fed SS or FF feed for the remainder of the study. After 11 wks adaptation to feeding, a subset of mares were evaluated with hourly blood samples for 24 h to assess glycemic and insulinemic response to three times daily feeding while on pasture. Neonatal foal FSIGTs (n=20) were conducted at 5 ± 1 d of age. The minimal model of glucose and insulin dynamics was used to determine insulin sensitivity (SI), glucose effectiveness (Sg), acute insulin response to glucose (AIRg) and disposition index (DI). Pregnant mares during Period 1 exhibited lowered SI, Sg and elevated AIRg relative to non-pregnant mares. Pregnant mares demonstrated greater glycemic and insulinemic responses to feeding of both SS and FF meals than non-pregnant mares consuming the same feeds. Also, SS feed elicited greater glycemic and insulinemic areas under the curve following feeding than FF feed in pregnant mares. These data support that pregnancy in mares in associated with lowered SI by 28 wks gestation and that altered SI, Sg and AIRg are associated with different responses to consuming SS and FF feeds. Foals exhibited high basal glucose, basal insulin, SI and Sg relative to mature horses, indicating a large capacity for glucose uptake with or without insulin. Basal glucose concentrations were higher and basal insulin concentrations tended to be higher in SS than FF foals (P = 0.016 and P = 0.071, respectively). Glucose and insulin dynamics in late gestation mares and neonatal foals exemplify the adaptive nature of energy metabolism in horses. Furthermore, dietary energy composition affects glucose and insulin responses to feeding in late gestation mares, which in turn was associated with different basal blood concentrations of these variables in the resulting neonatal foals. / Master of Science

Master of Science / Department of Animal Sciences and Industry / Timothy G. Rozell / Several alternatively-spliced mRNA transcripts of the follicle stimulating hormone receptor (FSHR) have been identified in sheep, including FSHR-1 (G protein-coupled form), FSHR-2 (dominant negative form), and FSHR-3 (growth factor type-1 form). Coupling of the FSHR to signaling pathways which activate different downstream effectors leads to speculation that specific splice variants may be transcribed under differing physiological conditions. This is the first study to correlate expression patterns of FSHR-1, FSHR-2, and FSHR-3 and development of follicles in the mature sheep ovary. In Experiment 1, 8 Suffolk-cross ewes were allowed to come into estrus naturally and were euthanized 24 (n=3), 36 (n=3), and 48 (n=2) hours after the onset of estrus. In Experiment 2, 7 Suffolk-cross ewes received CIDRs for 14 days. At CIDR removal, PMSG (500IU) was administered to treatment ewes (n=3), while controls (n=4) received no PMSG. Ewes were euthanized 24 (n=4; 2 CIDR only, 2 PMSG) or 36 (n=3; 2 CIDR only, 1 PMSG) hours later. All visible follicles were aspirated and pooled according to follicular diameter: small (≤ 2.0 mm), medium (2.1-4.0 mm), large (4.1-6.0 mm), and preovulatory (≥ 6.1 mm). Granulosa cells were separated from follicular fluid by centrifugation. Total RNA was extracted from granulosa cells (GC) and reversed transcribed. The resulting cDNA was subjected to qPCR, using primer sets designed to amplify each variant specifically. For Experiment 1, regardless of time after onset of estrus, relative expression of FSHR-3 exceeded that of both FSHR-1 and FSHR-2 in medium follicles (p < 0.01), and tended to be higher in small follicles (p=0.09). For Experiment 2, treatment with PMSG did not significantly alter expression patterns of FSHR variants (p=0.18). The FSHR-3 was expressed higher than FSHR-2 in all follicle sizes (p < 0.01) and was numerically more highly expressed than FSHR-1, although this difference was not significant (p > 0.11). These experiments show that in addition to the well characterized G protein-coupled form of the FSHR, alternatively spliced variants of the FSHR may participate in follicular dynamics during the first follicular wave of the sheep estrous cycle. Furthermore, these results would indicate that an “alternatively” spliced form of the FSHR (FSHR-3) is the predominant form of the FSHR in the sheep.