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.
Authors: Berryhill E H, Magdesian K G, Tadros E M, Edman J E
Journal: Veterinary journal (London, England : 1997)
Summary
# Editorial Summary Understanding glucose regulation in neonatal foals is essential for early detection of metabolic compromise, yet longitudinal data on healthy neonates remain limited. Berryhill and colleagues serially measured serum glucose, insulin and glucose/insulin ratios in seven foal–dam pairs at birth, days 1–2, and days 10–12 postpartum, sampling both pre- and post-suckling to capture the dynamic nature of neonatal metabolism. Whilst foals maintained glucose above 5 mmol/L throughout, they demonstrated substantial hourly fluctuations (up to 4.22 mmol/L in early life), with insulin varying maximally by 14.78 μU/mL by days 10–12; critically, glucose/insulin ratios increased significantly between birth and days 1–2, then stabilised. Mares exhibited pronounced transient insulin resistance immediately postpartum (median insulin 30.94 μU/mL and G/I ratio of 4.3), which resolved by later timepoints—a physiological adaptation distinct from their foals' metabolic profiles. These findings provide important reference ranges for clinicians evaluating sick neonates and suggest that wide glucose and insulin oscillations are normal in healthy foals rather than markers of pathology; practitioners should consider serial sampling and timing relative to feeding when interpreting metabolic bloodwork in neonates, and recognise that postpartum mares require monitoring for metabolic dysfunction independent of foal status.
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Practical Takeaways
- •Neonatal foals naturally exhibit wide glucose fluctuations in the first 2 weeks of life but this variability does not indicate pathology; baseline glucose should remain >5 mmol/L to rule out clinically significant hypoglycemia
- •Monitor postpartum mares for transient insulin resistance in the immediate post-partum period, which may influence metabolic management during this critical window
- •Suckling significantly elevates foal serum glucose compared to pre-suckle measurements, emphasizing the importance of adequate colostrum and early nursing for metabolic stability
Key Findings
- •Pre-suckle glucose concentrations in foals were significantly lower than post-suckle (5.15±1.61 mmol/L vs 7.16±3.13 mmol/L, P=0.0377)
- •Neonatal foals exhibited wide hourly variation in glucose (up to 4.22 mmol/L at 1-2 days and 2.93 mmol/L at 10-12 days) but remained >5 mmol/L with no hypoglycemia
- •Glucose/insulin ratios increased significantly from pre- and post-suckle periods to day 1-2 of age with no further changes
- •Postpartum mares demonstrated transient insulin resistance immediately post-partum with highest glucose (7.37 mmol/L median) and insulin concentrations (30.94 μU/mL median) compared to later timepoints and foals