Insulin resistance in pregnant mares: the influence of body condition

Abstract

Pregnancy is characterized by slight insulin resistance (IR), impaired glucose clearance and compensatory increased insulin secretion. More severe IR may, however, result in pancreatic β cell failure during pregnancy, and in turn leads to prolonged insulin insensitivity after birth, and/or an increased risk of diabetes in later life. This condition is known as gestational diabetes mellitus (GDM) in pregnant women those, in particular, who suffer from obesity. Although IR has been considered as a factor to increase the risk of laminitis and osteochondritis dissecans (OCD) in horses, there is no reported direct evidence showing that GDM occurs in pregnant mares. Hence, the present research aimed to study the occurrence of IR in pregnant mares with different body condition score (BCS) and potential long-term effects in the subsequent pregnancy.Experiment 1: In the first year, 13 pregnant mares were allocated into either a high body condition group (HBCS, n=6) or low body condition group (LBCS, n=7) based on BCS assessed at mid gestation on a scale of 1 to 9. The two groups were fed separately with either a high energy diet (150 % DE requirements) or a moderate energy diet (100 % DE requirements) to attain a BCS of HBCS ≥ 6 and LBCS ≤ 4, respectively, during the last trimester of pregnancy. Weekly blood samples were taken from week 41 to 46 of pregnancy to confirm the differences between the groups by determining the basal leptin concentrations. Frequently sampled intravenous glucose tolerance tests (FSIGTT) were performed at day 290 and 320 of gestation while insulin and glucose responses were analyzed by minimal model analyses to determine insulin sensitivity (Si), glucose effectiveness (Sg), acute insulin response to glucose (AIRg) and disposition index (DI).Experiment 2: In the subsequent year, lactating mares from the previous experiment were mated again prior to examinations for ongoing dysfunction of pancreatic β cell. Four mares from each of the previous HBCS and LBCS groups were selected for the study. During pregnancy animals were individually fed to ensure similarity in BCS between the groups and BCS were evaluated frequently.An oral glucose tolerance test (OGTT) was carried out at day 325 of gestation to study the insulin and glucose responses in late pregnancy.ii It was found in Experiment 1 that the BCS in the HBCS group was significantly (P<0.001) higher than those in the LBCS group at day 290 (6.3±0.4 vs. 4.1±0.3) and day 320 (7.2±0.5 vs. 3.3±0.3) of gestation. It was noted that BCS in the HBCS group was significantly (P<0.05) increased, whilst those in LBCS group significantly (P<0.01) decreased over the period. Live weight was, however, similar (p>0.05) between the groups during the period. In addition, Plasma leptin was significantly higher (P<0.05) in the HBCS group as compared to those in the LBCS group from week 41 to 46 of gestation. There was no significant difference found (p>0.05) in basal insulin or glucose levels between the groups at either day 290 or day 320 of gestation. No sig...

Glucose and insulin curve in pregnant mares and its relationship with clinical and biometric features of newborn foals

“…Metabolic dysregulation was associated with obesity in pregnant mares and women in other studies (George et al 2009, Catalano 2010, Peugnet et al 2015. Conversely, Song (2014) found insulin dysregulation in mares with low BCS due to β-pancreatic cell deficiency.…”