Effects of age on serum glucose and insulin concentrations and glucose/insulin ratios in neonatal foals and their dams during the first 2 weeks postpartum.

Maintaining serum glucose concentrations is critical in neonatal foals and is often dysregulated in illness; however, few studies have assessed the effects of age, or variation of glucose and insulin, in neonates and their postpartum dams. This study aimed to serially evaluate serum glucose and insulin concentrations and glucose/insulin (G/I) ratios in seven healthy foals and their dams immediately postpartum and at 1-2 and 10-12days of age. The hypotheses were that: (1) there would be wide temporal variation in hourly glucose and insulin measurements among foals; and (2) measured parameters in foals would differ from those of postpartum mares. Pre-suckle glucose concentrations were lower than post-suckle (5.15±1.61mmol/L and 7.16±3.13mmol/L, respectively, P=0.0377). Glucose remained >5mmol/L but varied hourly by up to 4.22mmol/L and 2.93mmol/L for individual foals 1-2 and 10-12days old, respectively. There were no significant changes in insulin over time (median 8.50 [4.32-18.4]μU/mL, 1-2days old) in foals. The maximum hourly variation of insulin for an individual foal was 7.53μU/mL and 14.78μU/mL (1-2days and 10-12days old, respectively). Glucose/insulin ratios increased from pre- and post-suckle to the 1-2days old period, with no significant changes thereafter. Mares had highest glucose and insulin concentrations and lowest G/I ratios immediately postpartum compared to later time points and to foals (median 7.37 [range, 4.34-8.78]mmol/L, median 30.94 [range, 20.35-49.20]μU/mL, 4.3 [2.43-7.04], respectively). In conclusion, neonatal foals exhibited wide variation in serum glucose and insulin concentrations but were not hypoglycemic. Mares developed transient insulin resistance in the immediate post-partum period.