New Test May Help Veterinarians Identify Life-Threatening Hormone Dysfunction in Sick Foals

Every minute counts when a newborn foal becomes critically ill. While veterinarians often focus on fighting infection, supporting blood pressure, and maintaining hydration, another vital system may quietly determine whether that foal survives: the endocrine system.

New research published in the Journal of Veterinary Internal Medicine suggests that a simple arginine vasopressin (AVP) stimulation test could provide veterinarians with a more reliable way to identify hypothalamic-pituitary-adrenal axis (HPAA) dysfunction in hospitalized foals—potentially allowing earlier treatment and improved survival.

Why the Endocrine System Matters

Newborn foals enter the world with an endocrine system that is still developing. During severe illness, the hypothalamic-pituitary-adrenal axis (HPAA) normally responds by releasing a cascade of hormones, including corticotropin-releasing hormone (CRH), adrenocorticotropic hormone (ACTH), arginine vasopressin (AVP), and cortisol.

Cortisol plays a critical role in helping the body respond to stress, maintain blood pressure, regulate metabolism, and survive critical illness. If a foal cannot produce an adequate hormonal response, its prognosis worsens significantly.

"Proper HPAA function is essential for survival in sick foals," explained lead investigator Dr. Katarzyna Dembek, associate professor of equine medicine at North Carolina State University.

The Problem with Current Testing

Veterinarians have traditionally relied on ACTH stimulation testing to evaluate adrenal function in horses. However, previous studies have shown that this test is often unreliable in critically ill neonatal foals.

Because AVP naturally stimulates ACTH release—and serves as the primary ACTH-releasing hormone in horses—the research team wanted to determine whether an AVP stimulation test could provide a more accurate picture of endocrine function.

Inside the Study

Researchers evaluated 60 foals less than one week of age:

• 15 healthy foals

• 19 septic foals

• 26 hospitalized foals that were ill but not septic

Each foal received a 5 IU dose of arginine vasopressin. Blood samples were collected before administration and again at 15, 30, 60, and 90 minutes to measure ACTH and cortisol concentrations.

What They Found

Healthy foals showed a rapid increase in both ACTH and cortisol within 15 to 30 minutes after receiving AVP.

Hospitalized foals also responded, but septic foals demonstrated a markedly weaker hormonal response. Their ACTH and cortisol concentrations were significantly lower than those of healthy foals, and the hormones increased more slowly following stimulation.

Researchers found that both diminished ACTH release and reduced cortisol production closely correlated with disease severity.

Perhaps even more intriguing, foals that showed little or no cortisol response after stimulation may have been premature, suggesting the test could provide valuable diagnostic information beyond identifying critical illness.

Why This Matters Clinically

The findings could have important implications for neonatal intensive care.

Detecting HPAA dysfunction earlier would allow veterinarians to identify foals that may benefit from hydrocortisone supplementation before endocrine failure becomes life-threatening.

Hydrocortisone therapy is already recognized as a valuable treatment option in foals with adrenal insufficiency, but identifying which patients need it has remained challenging.

The AVP stimulation test may help bridge that gap.

Researchers also note that the same diagnostic approach is currently being investigated for critically ill adult horses, potentially expanding its usefulness beyond neonatal medicine.

A Practical Diagnostic Tool

One of the advantages of AVP is that it is already widely available, relatively inexpensive, and compatible with equine patients.

While additional research is still needed before the test becomes routine clinical practice, the study suggests AVP stimulation testing could become an important addition to equine critical care.

For veterinarians managing septic or critically ill foals, having a better method to evaluate adrenal function may ultimately mean earlier intervention—and more foals surviving those critical first days of life.

The study, "Vasopressin Stimulation Testing in Hospitalized Foals," was published July 27, 2026, in the Journal of Veterinary Internal Medicine. The research was supported by the Morris Animal Foundation and Zomedica Inc.