Glucagon, insulin, adrenocorticotropic hormone, and cortisol in response to carbohydrates and fasting in healthy neonatal foals.
Authors: Kinsella Hannah M, Hostnik Laura D, Rings Lindsey M, Swink Jacob M, Burns Teresa A, Toribio Ramiro E
Journal: Journal of veterinary internal medicine
Summary
# Editorial Summary Healthy newborn foals undergo substantial metabolic adjustments during their first days of life, yet characterising their hormonal responses to different feeding and fasting conditions has remained largely unexplored. Researchers administered either intravenous glucose, oral glucose, oral lactose, or fasting protocols to 22 neonatal Standardbreds (≤4 days old) and measured plasma glucagon, insulin, ACTH and cortisol every 15 minutes over 210 minutes, with nursing permitted in the final half hour. Whilst oral lactose suppressed glucagon concentration at 45, 90 and 180 minutes compared to baseline, the most striking finding was nursing's dramatic effect: all foals showed marked increases in both glucagon and insulin within minutes of nursing (P <0.001), alongside simultaneous reductions in stress hormones ACTH and cortisol (P <0.01). These results suggest that bioactive components in mare's milk—beyond simple carbohydrates—potently regulate both pancreatic and hypothalamic-pituitary-adrenal function in the immediate postnatal period. For practitioners monitoring neonatal foal health, this reinforces the critical metabolic importance of early, frequent nursing and highlights that disrupted nursing patterns may compromise endocrine homeostasis; additionally, interventions using simple carbohydrate supplementation alone may be insufficient to replicate milk's complex hormonal signalling effects.
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Practical Takeaways
- •Nursing in newborn foals triggers substantially greater endocrine responses than administration of carbohydrates alone, indicating that milk composition beyond glucose and lactose is critical for normal metabolic adaptation in the immediate postnatal period
- •Understanding that neonatal foals suppress ACTH and cortisol during nursing while increasing insulin and glucagon suggests milk provides signals that shift metabolism away from stress response toward anabolic processes
- •Orphaned or bottle-fed foals may require specific attention to replicating milk constituents beyond carbohydrates to ensure appropriate endocrine responses during critical early development
Key Findings
- •Nursing stimulated marked increases in plasma glucagon, serum insulin, and glucose concentrations across all test groups (P<0.001), with greater effect than carbohydrate administration alone
- •Plasma ACTH and serum cortisol increased at 180 minutes during fasting and oral lactose administration (P<0.05 and P=0.04 respectively), but decreased following nursing (P<0.01)
- •Oral lactose administration decreased plasma glucagon at 45, 90, and 180 minutes relative to baseline (P=0.03), whereas IV and oral glucose administration showed no significant glucagon suppression
- •Factors in milk beyond carbohydrates appear to be strong direct or indirect stimulators of the endocrine pancreas and hypothalamic-pituitary-adrenal axis in neonatal foals