BackgroundThe enteroinsular axis (EIA) comprises intestinal factors (incretins) that stimulate insulin release after PO ingestion of nutrients. Glucose‐dependent insulinotropic polypeptide (GIP) and glucagon‐like peptide‐1 (GLP‐1) are the main incretins. The EIA has not been investigated in healthy neonatal foals but should be important because energy demands are high in healthy foals and dysregulation is frequent in sick foals.Objectives and HypothesisTo evaluate the EIA response to carbohydrates or fasting in newborn foals. We hypothesized that incretin secretion would be higher after PO versus IV carbohydrate administration or fasting.AnimalsThirty‐six healthy Standardbred foals ≤4 days of age.MethodsProspective study. Blood was collected before and after a PO glucose test (OGT; 300, 500, 1000 mg/kg), an IV glucose test (IVGT; 300, 500, 1000 mg/kg), a PO lactose test (OLT; 1000 mg/kg), and fasting. Foals were muzzled for 240 minutes. Blood was collected over 210 minutes glucose, insulin, GIP, and GLP‐1 concentrations were measured.ResultsOnly PO lactose caused a significant increase in blood glucose concentration (P < .05). All IV glucose doses induced hyperglycemia and hyperinsulinemia. Concentrations of GIP and GLP‐1 decreased until foals nursed (P < .05), at which time rapid increases in glucose, insulin, GIP, and GLP‐1 concentrations occurred (P < .05).Conclusions and Clinical ImportanceHealthy newborn foals have a functional EIA that is more responsive to milk and lactose than glucose. Non‐carbohydrate factors in mare's milk may be important for EIA activity. Constant exposure of intestinal cells to nutrients to maintain EIA activity could be relevant to management of sick foals. Foals can be fasted for 4 hours without experiencing hypoglycemia.

Background: The endocrine pancreas and hypothalamic-pituitary-adrenal axis (HPAA) are central to energy homeostasis, but information on their dynamics in response to energy challenges in healthy newborn foals is lacking. Objectives: To evaluate glucagon, insulin, ACTH, and cortisol response to fasting and carbohydrate administration in healthy foals. Animals: Twenty-two healthy Standardbred foals ≤4 days of age. Methods: Foals were assigned to fasted (n = 6), IV glucose (IVGT; n = 5), PO glucose (OGT; n = 5), and PO lactose (OLT; n = 6) test groups. Blood samples were collected frequently for 210 minutes. Nursing was allowed from 180 to 210 minutes. Plasma glucagon, ACTH, serum insulin, and cortisol concentrations were measured using immunoassays. Results: Plasma glucagon concentration decreased relative to baseline at 45, 90, and 180 minutes during the OLT (P = .03), but no differences occurred in other test groups. Nursing stimulated marked increases in plasma glucagon, serum insulin, and glucose concentrations in all test groups (P < .001). Plasma ACTH concentration increased relative to baseline at 180 minutes (P < .05) during fasting and OLT, but no differences occurred in other test groups. Serum cortisol concentration increased relative to baseline during OLT at 180 minutes (P = .04), but no differences occurred in other test groups. Nursing resulted in decreased plasma ACTH and serum cortisol concentrations in all test groups (P < .01). Conclusions and Clinical Importance: The endocrine response to enterally and parenterally administered carbohydrates, including the major endocrine response to nursing, suggests that factors in milk other than carbohydrates are strong stimulators (directly or indirectly) of the endocrine pancreas and HPAA.

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