Researchers have found that an arginine vasopressin stimulation (AVP) test offers a reliable way to test the endocrine function of sick foals. The work could lead to faster identification, treatment and improved survival rates for foals with hypothalamic-pituitary-adrenal gland axis (HPAA) dysfunction.
Proper function of the endocrine system – responsible for releasing hormones into the bloodstream – is critical to the survival of newborn foals. Unfortunately, these same foals are at the greatest risk of hormonal dysfunction because their endocrine systems are not fully developed when they are born. If a newborn foal falls ill and their endocrine system doesn’t respond appropriately, their chances of survival go down.
“The HPAA in particular is important for foal survival,” says Katarzyna Dembek, associate professor of equine medicine at North Carolina State University. “That’s because when a foal is sick, it stimulates the HPAA to release a cocktail of hormones: adrenocorticotropic hormone (ACTH); corticotropin-releasing hormone (CRH); arginine-vasopressin (AVP); and cortisol, the stress hormone, which helps the body survive critical illnesses.”
“ACTH stimulation – which tells the adrenal cortex to produce cortisol – is the current gold standard method for testing endocrine function in horses, although studies have shown poor reliability and performance in critically ill foals,” Dembek says.
“Arginine vasopressin (AVP) stimulates ACTH release and it has the additional advantage of being the primary adrenocorticotropin-releasing hormone in horses. We wanted to determine whether AVP stimulation would be useful for testing endocrine function in foals.”
Dembek and the research team looked at a cohort of 60 newborn (less than 1-week-old) foals: 15 healthy, 19 septic, and 26 sick but not septic. They administered AVP and then measured both ACTH and cortisol levels in the blood at 15-, 30-, 60- and 90-minute intervals following administration.
They found that ACTH and cortisol concentrations increased in all groups 15 to 30 minutes after AVP administration. In septic foals, they saw that both the ACTH and cortisol levels were lower than in other groups, and that they didn’t increase as rapidly as in other groups.
The researchers found the results promising, not just for diagnosing HPAA dysfunction, but as a potential indicator of prematurity in foals.
“This study shows that AVP stimulation is promising in determining how sick a foal may be, and could aid in early intervention, particularly in foals without a lot of clinical signs of illness,” Dembek says. “And in foals where we saw no real change from baseline, the lack of cortisol production could indicate that they are premature.”
Early diagnosis of HPAA dysfunction and lack of cortisol enables the use of hydrocortisone therapy in sick foals to enhance their chances of survival. A similar approach – currently being studied by Dembek – can also be applied to critically ill adult horses.
“AVP is widely available for use, compatible with horses, and largely affordable,” Dembek says. “Its use in diagnosing HPAA dysfunction warrants further exploration.”
The work appears in the Journal of Veterinary Internal Medicine and was supported by the Morris Animal Foundation and Zomedica Inc. First author Myriah Albrecht is currently a resident at The Ohio State University. Other contributors include Javier Perez DVM in private practice; David Wong from Iowa State University; Nimet Browne from the Hagyard Equine Medical Institute; Teresa Burns from The Ohio State University; and Maddie Edwards Stevens from the Oklahoma City Equine Clinic.
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