# Omic technology to monitoring resilience and adaptation to exercise and heat stress in endurance horses

## TL;DR

This study explores how endurance horses adapt to heat and exercise stress by analyzing molecular changes in their blood.

## Contribution

The study identifies specific small RNAs and molecular pathways involved in resilience to combined heat and exercise stress in horses.

## Key findings

- Heat stress increases lactatemia and hematocrit in horses compared to thermoneutral conditions.
- Differentially expressed small RNAs like eca-mir-301 and eca-mir-144 are modulated by temperature and exercise.
- Molecular pathways related to immune regulation and oxidative stress are enriched under heat stress.

## Abstract

In horses, heat exposure modulates the hypothalamic-pituitary-adrenal axis, autonomic nervous system, and hypothalamic-pituitary-thyroid axis to maintain body temperature and prevent excessive heat accumulation. However, during strenuous exercise under hot and humid conditions, heat production may exceed dissipation, leading to heat stress, anhidrosis, heat stroke, or brain damage.

Incremental field standardized exercise tests (fSETs) provide a reliable approach to assess training and fitness levels. Six Arabian horses from Italia Endurance Stable and Academy were monitored during fSETs performed under heat stress (HS) and thermoneutral (TN) conditions, with blood samples collected before and after each test. Hematocrit, lactate, and biochemical parameters were measured, and total serum RNA was sequenced. A protein-protein interaction (PPI) network of miRNA targets was constructed and analyzed for Gene Ontology (GO) enrichment.

Lactatemia and hematocrit were significantly higher in HS vs. TN, while alanine aminotransferase, creatinine, and creatine kinase increased in HS POST vs. PRE fSET. Differentially expressed small RNAs included eca-myomir-206, eca-mir-301, eca-mir-3613-3p, eca-mir-142, and eca-mir-144, which were modulated by temperature and exercise. In POST vs. PRE fSET, enriched terms involved transcriptional regulation, glucose and LDL response, intracellular trafficking, cytoskeleton organization, cardiac conduction, ion channels, and immune regulation. In HS POST vs. PRE fSET, enrichment was observed for positive regulation of dendritic cell cytokine production, negative regulation of inflammation, and attenuation of oxidative stress-induced apoptotic signaling.

This study aimed to investigate the molecular features underlying resilience and adaptation to combined heat- and exercise-induced stress in horses. Overall, our findings indicate that heat amplifies the physiological burden of endurance exercise and alters the molecular mechanisms supporting performance and recovery. Circulating small RNAs may act as early signals for homeostatic restoration and could help elucidate adaptive responses to stress, guiding personalized training strategies.