The effects of extended photoperiod and warmth on hair growth in ponies and horses at different times of year.
Authors: O'Brien Christiane, Darcy-Dunne Megan Ruth, Murphy Barbara Anne
Journal: PloS one
Summary
# Editorial Summary: Extended Photoperiod and Coat Management in Horses and Ponies Seasonal coat changes in equines are primarily driven by photoperiod, with lengthening or shortening days triggering shifts in melatonin and prolactin that regulate moulting and winter coat development. O'Brien and colleagues conducted four separate longitudinal studies using commercially available head-mounted light masks delivering approximately 15 hours of daily light exposure, combined with rugs where necessary, to determine whether artificial photoperiod extension could manipulate coat growth patterns when applied at different times of year. Results demonstrated markedly variable outcomes depending on timing: artificial light proved ineffective at preventing winter coat initiation when applied from the autumn equinox, successfully maintained summer coats in stabled horses when begun one month after the summer solstice, accelerated shedding in outdoor-living horses started one month before the winter solstice, yet failed to enhance shedding in ponies regardless of timing or housing. The critical practical implication is that light therapy efficacy is highly dependent on both application timing and environmental temperature management; farriers, veterinarians and yard managers cannot assume a one-size-fits-all approach to coat control, particularly for breeding mares or competition horses requiring consistent cosmetic or thermoregulatory status. Future work examining breed-specific responses and management variations would help refine protocols for practitioners seeking to optimise coat management whilst maintaining appropriate thermal regulation.
Read the full abstract on PubMed
Practical Takeaways
- •Light masks can maintain summer coats in competition horses if started early (one month after summer solstice), but timing is critical—starting too late won't work
- •For horses that need to shed winter coats, light masks work best when applied one month before winter solstice; effectiveness varies with housing (outdoor horses respond better than indoor)
- •Combining light extension with temperature management is essential—you cannot rely on light masks alone without considering the horse's thermal needs and living conditions
Key Findings
- •Extended photoperiod initiated one month post-summer solstice effectively maintained summer coat in stabled horses
- •Extended photoperiod initiated one month pre-winter solstice accelerated shedding in outdoor-living horses
- •Extended photoperiod initiated at autumnal equinox did not reverse winter coat growth
- •Timing of light application is crucial for successful management of equine coat growth while preserving thermoregulation