Horses with previous episodes of laminitis have altered insulin responses to seasonal oral sugar testing and grazing compared to horses with no known history of laminitis.

Forage is essential for equine health and performance, but intake of elevated pasture nonstructural carbohydrates (NSC) may exacerbate metabolic disorders. This study aimed to investigate the influence of laminitis history on metabolic and morphometric responses in grazing horses. Twelve non-pregnant mares (15 ± 3.4 yrs) were selected based on previous diagnosis of laminitis (PRELAM; n=6) or not (NOLAM; n=6). Horses were maintained on 8.5-ha pasture. Weekly pasture samples were clipped at random for nutrient analysis. Monthly blood samples were collected and analyzed for glucose and insulin concentrations. Body weight (BW), body condition score (BCS), and cresty neck score (CNS) were evaluated monthly. Each month, a modified oral sugar test (OST) was used to assess basal (T0) and 75-minute (T75) insulin dynamics following 0.30 mL/kg BW Karo Light Corn Syrup. Data were analyzed using PROC MIXED with repeated measures (SAS Institute). PRELAM had greater CNS (P < 0.001), BW (P < 0.05), and BCS compared to NOLAM (P < 0.05). Non-fasted glucose was influenced by month (P < 0.001) while non-fasted insulin was affected by group by month (P = 0.004). Fasted insulin concentrations (T0) were affected by month and group (P < 0.001) where PRELAM had greater concentrations. T75 glucose and insulin concentrations were affected by month (P < 0.001 and P = 0.002, respectively) and were higher for PRELAM (P = 0.003). These data suggest horses with greater general and regional adiposity, and previous history of laminitis, often exhibit greater insulin concentrations on pasture and to OST.