Perinatal Stress in Immature Foals May Lead to Endocrine Dysregulation in Adults

Perinatal Stress in Immature Foals May Lead to Subclinical Adrenocortical Dysregulation in Adult Horses: Pilot Study
J Equine Vet Sci. 2022 Jan 21;103869. doi: 10.1016/j.jevs.2022.103869. Online ahead of print.
Authors
Jane Clothier 1 , Alison Small 2 , Geoff Hinch 3 , Wendy Y Brown 4
Affiliations

1 Agriculture and Food, CSIRO, New England Highway, Armidale, NSW 2350, Australia; Canine and Equine Research Group, University of New England, Armidale, NSW 2351; School of Environmental and Rural Science, University of New England, Armidale, NSW 2351. Electronic address: jane@equinehealthworks.com.
2 Agriculture and Food, CSIRO, New England Highway, Armidale, NSW 2350, Australia; Canine and Equine Research Group, University of New England, Armidale, NSW 2351.
3 School of Environmental and Rural Science, University of New England, Armidale, NSW 2351.
4 Canine and Equine Research Group, University of New England, Armidale, NSW 2351; School of Environmental and Rural Science, University of New England, Armidale, NSW 2351.

Abstract

The persistent endocrinological effects of perinatal stress due to gestational immaturity in horses are unknown, although effects have been reported in other livestock species. This pilot study tested the hypothesis that persistent adrenocortical dysregulation is present in horses that were gestationally immature at birth by assessing the salivary cortisol response to exogenous ACTH. Case horses (n = 10) were recruited with histories of gestation length < 315 d or dysmaturity observable through neonatal signs. Positive controls (n = 7) and negative controls (n = 5) were recruited where possible from related horses at the same locations. Cases and positive controls received an intramuscular, low-dose (0.1 ug/kg) of synthetic ACTH (Tetracosactrin 250 mg/mL, Synacthen®); negative controls received no ACTH. Saliva samples were collected from all horses at baseline T = 0 and at 30 min intervals post injection from T = 30 to T = 150. These were assayed for salivary cortisol concentration (SCC) using a commercially available ELISA kit (Salimetrics®). All baseline values (T = 0) were within normal published ranges. Peak and AUC values (corrected for baseline) for case horses were significantly different (ANOVA P < 0.001) to positive controls, with either higher (H-cases) or lower (L-cases) SCC values, outside the 95% Confidence Interval of the reference population. There was no significant effect of breed, age, sex, test month, or location on results. The results suggest that gestational immaturity may lead to subclinical adrenocortical dysregulation, with affected horses presenting an elevated or blunted response to a low-dose ACTH stimulation, despite normal basal levels. Keywords: Premature foals; developmental programming; dysmature foals; fetal programming; hypoadrenocorticism; relative adrenal insufficiency.