Giving magnesium and boron can benefit headshaking horses, the findings of research suggest.
Trigeminal‐mediated headshaking, which used to be called idiopathic headshaking, is caused by a low threshold of firing of the trigeminal nerve in the face.
In most cases, the condition is worse during spring and summer, and geldings are over-represented.
Various treatments have been tried, including face masks with ultraviolet light protection, nose nets, nutritional supplements, antihistamines, corticosteroids, neuromodulation, and even surgery on the nerve.
Results have been variable.
Unsuccessful management can leave horses with uncontrollable clinical signs, often leading to poor performance, wastage, and, in severe cases, euthanasia.
Owners in a survey indicated that magnesium supplementation decreased headshaking behavior in 40% of horses with an over-sensitive trigeminal nerve.
Some horses affected with trigeminal‐mediated headshaking have ionized magnesium concentrations below normal levels, and giving them an infusion of magnesium sulfate has been shown in a study to decrease headshaking by 29%.
Researchers at the University of California, Davis, set out to see whether adding magnesium and boron to the diet of affected horses would influence headshaking behavior.
Their study, reported in the Journal of Veterinary Internal Medicine, also included boron supplementation, as it is known to increase ionized magnesium concentrations in the blood.
Shara Sheldon and her colleagues hypothesized that magnesium supplementation with or without boron would decrease headshaking. They also hypothesized that boron would enhance magnesium absorption, further increasing blood concentrations of ionized magnesium and further decrease headshaking.
Their study involved six healthy geldings used as controls and six geldings diagnosed with trigeminal‐mediated headshaking.
The experiment ran over 42 days, with the horses divided into three groups to be rotated through three week-long diets.
One diet comprising hay and a pelleted feed combined with a quarter of a cup of canola oil and two tablespoons applesauce. Another comprised hay and the pelleted feed combination supplemented with magnesium. The third diet comprised hay and the pelleted feed combination supplemented with both magnesium and boron.
The magnesium was given in the form of magnesium citrate, at a rate of 24.2 milligrams per kilogram of body weight, and the boron was given as boron citrate at a rate of 2 milligrams per kilogram of body weight.
The horses had a washout period of a week between each diet, during which they received only hay.
Blood samples were taken for biochemical analysis at the start of the study, when horses had been on a hay-only diet for a week, and after each week of supplementation.
All three diets were found to increase the levels of ionized and total magnesium in blood when compared to the baseline hay diet. However, these levels were highest in the horses receiving the magnesium and magnesium-boron combination.
Horses receiving the three treatments had a significant reduction in headshaking when compared to the hay-only diet.
Magnesium in combination with boron had the greatest effect, assessed as a 64% reduction in headshaking when compared to the hay diet only. This combination reduced headshaking by 36% when compared to the diet of hay and pelleted feed.
The most severely affected horses were found to enjoy the greatest benefit of magnesium supplementation.
“Oral supplementation with magnesium or magnesium in combination with boron should be considered in horses affected with headshaking,” they said.
“The increased response to boron should be investigated further,” they added.
The researchers acknowledged that their study involved a small number of horses and only short‐term supplementation.
“A longer duration of magnesium supplementation would have been useful to investigate the long‐term effects in headshaking behavior,” they said.
“Although the overall decrease in headshaking behavior in this group of six horses might not reflect the effects on the headshaking population at large, this is a promising therapeutic option that should be investigated in a broader population of horses affected with trigeminal‐mediated headshaking.
“Although magnesium supplementation did not completely alleviate all headshaking behavior, a reduction might improve the horse’s quality of life and performance, make a horse rideable or manageable, and avoid euthanasia.”
Magnesium supplementation could be considered, especially if ionized magnesium was low, as was found in the horses with headshaking in this study, they said.
Supplementation with magnesium could be considered as an adjunct to other treatment attempts for the management of the condition, they said.
The full study team comprised Sheldon, Monica Aleman, Lais Costa, Kalie Weich, Quinn Howey and John Madigan, all with the University of California, Davis.
Effects of magnesium with or without boron on headshaking behavior in horses with trigeminal‐mediated headshaking
Shara A. Sheldon, Monica Aleman, Lais R.R. Costa, Kalie Weich, Quinn Howey, John E. Madigan
Journal of Veterinary Internal Medicine, 16 April 2019, https://doi.org/10.1111/jvim.15499