Background: Oral administration of magnesium and boron might have a beneficial effect on headshaking behavior in horses. Objective: Evaluate the effects of oral magnesium alone or in combination with boron on headshaking behavior in affected horses. Animals: Twelve geldings (6 healthy controls and 6 affected). Methods: Prospective randomized controlled dietary trial over 42 days in 12 horses (6 horses diagnosed with trigeminal-mediated headshaking and 6 unaffected healthy controls). All horses received a hay diet and were randomized into 3 treatment groups: pelleted feed combination (PF), pelleted feed combination with magnesium (M), and pelleted feed combination with magnesium-boron (MB) with a week washout of hay only between treatments. Headshaking behavior and biochemical blood variables were assessed at baseline (hay only) and then after each week of supplementation. Results: All 3 diet interventions increased blood ionized and total magnesium. Groups M and MB further increased Mg 2+ when compared to PF. Horses receiving treatments had a significant reduction in headshaking behavior, as measured by incidence rate ratio (IRR), when compared to unsupplemented hay diet (44% for PF, IRR, 0.558; CI, 0.44, 0.72; P <.001; 52% for M, IRR, 0.476; CI, 0.37, 0.62; P <.001; and 64% for MB, IRR, 0.358; CI, 0.27, 0.48; P <.001). Conclusions and Clinical Importance: Magnesium in combination with boron had the greatest decrease in headshaking. Oral supplementation with magnesium or magnesium in combination with boron should be considered in horses affected with headshaking.
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