Interplay Among the Daily Rhythm of the Thyroid Hormones, Uncoupling Protein 1 and the Clock Gene Per2 in Horses.
Authors: Giannetto Claudia, Arfuso Francesca, Giudice Elisabetta, Guercio Annalisa, Cannella Vincenza, Monteverde Vincenzo, Piccione Giuseppe
Journal: Journal of equine veterinary science
Summary
# Editorial Summary Maintaining thermal homeostasis is fundamental to equine health, yet how this regulatory system fluctuates across the 24-hour cycle remains poorly understood in horses. Giannetto and colleagues measured serum concentrations of thyroid hormones (T3 and T4), uncoupling protein 1 (UCP1), and the circadian clock gene Per2 in seven healthy mares housed under natural light and temperature conditions, with blood sampling every four hours across 48 hours. Both thyroid hormones demonstrated robust circadian rhythmicity—T3 peaked approximately five hours after sunrise whilst T4 peaked mid-night—with the Per2 clock gene expression synchronising near sunrise, yet UCP1 concentrations remained stable throughout the measurement period. These findings suggest that in horses maintained under naturalistic conditions without thermal stress, thyroid hormone secretion is tightly coordinated with circadian gene expression, potentially optimising metabolic heat production in response to anticipated daily temperature changes. For practitioners managing stabled horses, this work highlights that disrupted photoperiod or environmental instability could desynchronise these important regulatory rhythms, warranting consideration of natural lighting and temperature stability as components of injury prevention and general welfare management.
Read the full abstract on PubMed
Practical Takeaways
- •Thyroid hormone levels in horses naturally fluctuate throughout the day under normal housing conditions; timing of blood sampling for thyroid assessment should account for these circadian variations to avoid misinterpretation
- •Housing horses under natural photoperiod supports normal circadian organization of thyroid function and clock gene expression, which may contribute to improved thermal comfort and welfare
- •UCP1 stability suggests that in horses without thermal stress, metabolic heat production regulation may depend more on thyroid hormone dynamics than brown adipose tissue uncoupling protein expression
Key Findings
- •T3 demonstrates a diurnal rhythm with peak concentration approximately 5 hours after sunrise in healthy horses
- •T4 peaks during the middle of the dark phase (scotophase) showing nocturnal rhythm pattern
- •Clock gene Per2 expression peaks near sunrise, synchronizing with light-dark cycle
- •UCP1 (uncoupling protein 1) remained constant throughout the 48-hour observation period with no significant daily fluctuation