Circadian Variation of Peripheral Blood Cells in Horses Maintained in Different Environmental and Management Conditions.
Authors: Aragona Francesca, Arfuso Francesca, Fazio Francesco, De Caro Salvatore, Giudice Elisabetta, Monteverde Vincenzo, Piccione Giuseppe, Giannetto Claudia
Journal: Animals : an open access journal from MDPI
Summary
# Editorial Summary Researchers tracked blood cell profiles in horses over 48-hour periods across all four seasons, comparing animals housed in loose boxes versus paddocks and sampling every four hours to capture circadian rhythms. Housing conditions significantly influenced most haematological parameters (red cells, haemoglobin, haematocrit, platelets, and leukocyte populations), with seasonal changes also evident—particularly for red cells, haematocrit, platelets, and all white cell types except basophils. Circadian rhythm analysis revealed daily oscillations in blood parameters during spring in both housing types, whilst lymphocytes and neutrophils showed pronounced diurnal variation during spring and summer in stabled horses, and during winter in paddocked animals. These findings underscore that immune function and blood cell dynamics follow predictable circadian patterns influenced by both environmental exposure and management practices, suggesting that single-point blood samples may misrepresent an animal's true haematological status and that time of sampling warrants consideration in clinical assessment and comparative evaluations.
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Practical Takeaways
- •Timing of blood sampling matters: hematological values vary significantly by time of day and season, so standardize sampling times when comparing results or establishing baselines for individual horses
- •Housing conditions (loose box vs paddock) significantly affect immune parameters, suggesting that pasture access and movement opportunity influence overall health status beyond clinical observation
- •When evaluating a horse's health status or immune competence, consider the season and current housing/management conditions as these substantially alter normal reference ranges for WBC counts and differential populations
Key Findings
- •Housing conditions significantly affected all hematological values except WBC in winter (p<0.0001), indicating management environment influences immune parameters
- •Seasonal variation was significant for RBC, hematocrit, and platelets, with all leukocyte populations showing seasonal differences except basophils (p<0.0001)
- •Daily rhythms in hematological parameters were observed during spring in both housing groups, with lymphocytes and neutrophils showing circadian patterns that varied by season and housing type
- •Circadian physiology regulates immune system responses, demonstrating that temporal structure of adaptation to environmental conditions affects blood cell populations