Background Trigeminal‐mediated headshaking results from low‐threshold firing of the trigeminal nerve resulting in apparent facial pain. Magnesium may have neuroprotective effects on nerve firing that potentially dampen signs of neuropathic pain. This hypothesis has not been investigated in horses with trigeminal‐mediated headshaking. Objective To investigate head‐shaking behavior in affected horses after IV magnesium sulfate infusion. Animals Six geldings with trigeminal‐mediated headshaking. Methods Prospective randomized crossover study. Horses were controlled for diet and infused IV with 5% dextrose solution (DS; control solution at 2 mL/kg body weight [BW]) and MgSO4 50% solution (MSS at 40 mg/kg BW). Head‐shaking behavior was recorded at times T0 (baseline, before infusion) and T15, T30, T60, and T120 minutes post‐infusion. Venous blood variables such as pH, HCO3−, standard base excess (SBE), Na+, Cl−, K+, Ca2+, Mg2+, total magnesium (tMg), glucose, and lactate were measured; strong ion difference (SID) and anion gap (AG) were calculated for each time point. Results Blood variables including pH, Na+, Cl−, K+, SID, AG, lactate, Ca2+, tMg, and Mg2+ had significant changes with MSS as compared to DS treatment. Glucose, SBE, and HCO3− did not have significant changes. A 29% reduction in head‐shaking rate occurred after MSS treatment but no change occurred after DS treatment. Conclusions and Clinical Importance Administration of MSS IV increased plasma total and ionized magnesium concentrations and significantly decreased head‐shaking behavior in horses with trigeminal‐mediated headshaking.

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.

Simple SummaryHorses with trigeminal-mediated headshaking syndrome suffer from pain and electric-shock-like sensation in the nerve that runs across their faces (trigeminal nerve), leading to violent head jerking that impairs their performance and quality of life. This condition has no curative treatments and often leads to euthanasia of the animal. Changes in blood components (pH, electrolytes) are known to affect nerve pain. To investigate this, three different kinds of fluids (with varying pH and electrolytes) were given in the vein to horses affected with trigeminal-mediated headshaking. The headshaking behaviors and changes in blood composition were assessed after each treatment. Changes in blood composition were transient, and there was a greater than 50% decrease in headshakes/minute with a high pH treatment. The limited effects following these fluids were likely due to normal mechanisms of regulation of blood levels of these salts and minerals. Further investigations of changes in electrolytes that might affect nerve firing should be explored.AbstractTrigeminal-nerve-mediated headshaking represents a major welfare challenge for owners and veterinarians and is caused by a low threshold firing of the trigeminal nerve resulting in pain manifested as violent head jerking that often terminates the horse’s career and life due to poor quality of life and suffering. As metabolic changes such as acid–base status and electrolytes play a role in nerve firing, this study sought to assess the effects following administration of hypertonic solutions on headshaking behavior in affected horses. This prospective randomized controlled crossover design utilized six horses affected with trigeminal-mediated headshaking and three treatment groups receiving intravenous administration of 5% dextrose solution at 2 mL/kg bwt (DS), NaCl 7.5% at 4 mL/kg bwt (HS), or NaHCO3 8.4% at 2 mmol/kg bwt (HB). Horses were assessed for headshaking behavior changes at times T0 (baseline, before infusion) and T15, 30, 60, 120 min post infusion. Venous blood variables: pH, HCO3−, standard base excess (SBE), Na+, Cl−, K+, Ca2+, Mg2+, total magnesium (tMg), glucose, and lactate were measured at T0 (baseline, before infusion) and T5, 15, 30, 60, 120 min post infusion. Strong ion difference (SID) and anion gap (AG) were calculated for each time point. With HB treatment, there was greater than 50% reduction in headshaking rate. There was an effect of time on increasing headshaking rate. There was an effect of breed on headshaking rate. Changes in blood parameters following DS were virtually absent. Infusion of HS caused mild changes and did not vary much from baseline except for SID and AG. Only infusion of HB caused blood pH and HCO3− to be outside of the physiologic range (alkalemia and metabolic alkalosis, respectively), SBE to double or triple, AG to decrease, and SID to increase compared to baseline. Infusion of DS was followed by increase in blood glucose and decrease in blood Na+. Infusion of HS was followed by increase in Na+ and Cl− and decrea...

Thirty-six volatile compounds were positively identified in the dichloromethane extract of an aqueous solution of L-cysteine that was irradiated with UV light at 253.7nm for 24hr. The irradiated solution was colorless but has a cooked meat-like flavor. The compounds identified were thiophenes, pyrazines, thiazoles, thiazolines, thiazolidines, and polymethylene sulfides. 2-Methylthiazole was found in the largest quantity, approximately 40%of the extract. Proposed photochemical reactions of cysteine included Strecker degradation, isomerization, dimerization, and homolytic fission of CC , C-S, or S-H bonding.

Background Trigeminal‐mediated headshaking results from a low threshold for firing of the trigeminal nerve. A seasonal component has been implicated in onset of clinical signs, which occur during the spring and summer months. Geldings are overrepresented in the affected population and hormonal differences as compared to a healthy control population of geldings might contribute to headshaking. Objective/Hypothesis To assess concentrations of luteinizing hormone (LH) over an 8‐hour period in gelded healthy controls and horses affected with headshaking. Our hypothesis was that geldings with seasonal headshaking would have higher concentrations of LH over an 8‐hour period compared to control horses during the summer when affected horses manifested headshaking. Animals Twelve geldings (6 controls and 6 affected). Methods Prospective controlled trial. Blood samples were drawn every 15 minutes over an 8‐hour time period during summer from all horses to measure circulating LH concentrations by using a radioimmunoassay for equine LH. All affected horses were actively affected by headshaking at the time of sample collection. Results No statistically significant differences in LH concentrations were found throughout the study period in headshakers as compared to control horses. Time had no significant effect, but a slight decrease in LH concentrations was observed for all horses. The main limitation of the study was the low number of horses. Conclusions and Clinical Importance Horses affected with headshaking did not have significant differences in circulating LH during the late summer as compared to control horses.