Serum vitamin D, calcium, and phosphorus concentrations in ponies, horses and foals from the United States and Thailand.
Authors: Pozza Megan E, Kaewsakhorn Thattawan, Trinarong Chumnan, Inpanbutr Nongnuch, Toribio Ramiro E
Journal: Veterinary journal (London, England : 1997)
Summary
# Editorial Summary Vitamin D's role in calcium-phosphorus homeostasis and skeletal development makes understanding its status across different age groups and environments critical for equine practitioners, yet comparative data have remained limited—particularly for growing horses and in tropical climates. Researchers measured serum 25(OH)D₃, calcium, and phosphorus concentrations in Thoroughbred foals, yearlings, and adult horses from both the United States (Ohio/Kentucky) and Thailand (Chiang Rai and Kanchanaburi), sampling approximately 50 animals per region during the same seasonal period. Age emerged as a significant factor: foals consistently demonstrated lower 25(OH)D₃ concentrations than yearlings and adults in both countries, whilst phosphorus levels followed the inverse pattern, being elevated in foals regardless of geography; calcium concentrations remained stable across age groups and locations. These findings suggest that lower vitamin D status in young horses may represent a physiological norm rather than a geographic phenomenon, though the clinical implications of this age-related variation—particularly whether supplementation strategies should differ between foals and mature animals—warrant investigation in future studies. For practitioners, this work establishes reference data that will help distinguish normal developmental patterns from pathological dysregulation in calcium-phosphorus metabolism, informing nutritional and supplementation protocols for growing stock.
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Practical Takeaways
- •Young foals have lower vitamin D status than older horses regardless of climate; supplementation strategies may need to be age-adjusted to prevent calcium-phosphorus dysregulation during growth
- •Elevated phosphorus in foals is a normal age-related finding; monitor calcium-phosphorus ratios during development rather than focusing on absolute phosphorus values
- •Geographic location (temperate vs tropical) does not substantially alter vitamin D dynamics in horses, suggesting dietary and management factors may be more important than sunlight exposure alone
Key Findings
- •Serum 25(OH)D3 concentrations were significantly lower in foals compared to yearlings and adult horses in both US and Thailand locations
- •Phosphorus concentrations were higher in foals than older age groups in both countries, while calcium concentrations remained consistent across all groups
- •Age-related differences in 25(OH)D3 were independent of geographic location, with no significant differences between US and Thai horses