Variations in the concentration of zinc in the blood of Icelandic horses.
Authors: Kolm G, Helsberg A, Gemeiner M
Journal: The Veterinary record
Summary
# Editorial Summary: Zinc Distribution in Icelandic Horses Plasma zinc concentrations in horses vary substantially depending on farm management and environmental factors, yet this variation doesn't necessarily reflect whole blood or cellular zinc status—a distinction with important implications for interpreting diagnostic samples. Kolm and colleagues examined 104 Icelandic horses to understand how farm location, sex, age, and sweet itch susceptibility influence zinc distribution across plasma, whole blood, and blood cells, finding that whilst plasma zinc differed significantly between farms (P<0.01), the zinc content of whole blood and cells remained relatively stable. The researchers identified a striking disparity in compartmentalisation: blood cells contained 10.5 times more zinc than plasma, yet plasma zinc showed no correlation with either whole blood or cellular zinc due to highly variable proportions of total blood zinc in the plasma fraction (ranging from 9–24 per cent). This proportional variability was significantly influenced by a complex three-way interaction between farm, sex, and sweet itch status (P<0.05), with relative plasma zinc positively correlated to absolute plasma values (r=0.78) but negatively correlated to both whole blood and cellular zinc (r=-0.58 and -0.71 respectively). For practitioners relying on blood zinc assays for nutritional assessment or diagnosis, these findings suggest that farm-based and individual factors substantially affect how zinc distributes between plasma and cellular compartments, meaning single plasma measurements may not reliably indicate overall zinc status and should be interpreted cautiously alongside clinical signs and whole blood assessment.
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Practical Takeaways
- •Plasma zinc alone is not a reliable indicator of total body zinc status in horses; the distribution between plasma and cellular compartments varies substantially between individual animals
- •Farm environment appears to influence circulating plasma zinc levels, suggesting management or dietary factors warrant investigation in horses with suspected zinc deficiency
- •When interpreting zinc blood results in Icelandic horses, clinicians should consider that relative plasma zinc varies by sex and sweet itch status, potentially affecting diagnostic interpretation
Key Findings
- •Plasma zinc concentration varied significantly between farms (P<0.01), but whole blood and blood cell zinc were not influenced by farm, sex, age, or sweet itch status
- •Blood cell zinc concentration was 10.5 times greater than plasma zinc concentration
- •Relative plasma zinc (proportion of whole blood zinc present in plasma) ranged between 9-24% and was significantly influenced by three-way interaction of farm, sex, and sweet itch (P<0.05)
- •Relative plasma zinc was positively correlated with absolute plasma zinc (r=0.78, P<0.001) but negatively correlated with whole blood and cellular zinc (r=-0.58 to -0.71, P<0.001)