MEDICINE POTPOURRI: NEUROLOGY, FOALS, MUSCLES, AND THE GUT


summer. Eight horses (47%) responded positively to melatonin within 1 to 4 weeks of therapy; marked improvement was seen in 1 horse (the horse given melatonin in the morning) and some improvement in the remaining 7 (including the horse given mela- tonin twice daily) (Table 2). No change in head- shaking was reported in 9 (53%) of horses. Seven horses (41%) had a longer hair coat or did not shed their winter coat whilst on melatonin.


Magnesium


Dietary supplementation with magnesium had been used by 58/128 (45%) of owners as a headshaking treatment. Magnesium oxide was the most com- mon formulation reported (26 responses) followed by malate (7 responses). Doses of 5 to 40 g were re- ported. A positive outcome was reported in 25 horses (43%) within 2 days to 4 weeks of initiating therapy; additionally 1 owner reported headshaking worsened within a couple of days of stopping mag- nesium supplementation. One horse completely stopped headshaking, 11 (19%) showed marked im- provement, and 13 (22%) showed mild improvement (Table 2). A negative outcome was noted in 33 horses (57%) in which no change in headshaking was observed. Two owners reported that their horse seemed calmer whilst on magnesium, whereas 1 owner each reported nervousness and diarrhea as adverse effects.


Melatonin and Magnesium


Only 11/122 (9%) owners had used melatonin and magnesium combination therapy to treat their horses’ headshaking. Six horses (55%) responded positively with 5 horses (45%) showing some im- provement and 1 horse (10%) marked improvement in headshaking whereas 5 horses (45%) had no change (Table 2). All respondents who gave data (n  7) used a dosage of 15 to 20 mg melatonin (median 15 mg) at 5 PM and 5 to 40 g magnesium. Two owners initiated combination therapy in spring, 5 in summer, and 4 in winter. Adverse effects were observed in 4 horses (36%), 3 of which did not shed their winter coat and 1 which gained weight and became lethargic approximately 1 month after ther- apy was initiated.


4. Discussion


Treatment of headshaking horses is challenging as therapies are largely directed towards managing clinical signs rather than treating the cause itself, which remains elusive. There are a plethora of treatments recommended and utilized for manage- ment of headshaking; however, reported rates of success of such treatments are rare and often con- tain limited numbers of horses. This study de- scribes the owner-reported outcome of 11 treatments used in the management of idiopathic headshaking in 130 horses. The demographics of the survey population and prevalence of clinical signs were similar to that de-


180 2014  Vol. 60  AAEP PROCEEDINGS


scribed in other headshaking studies.7,8 Some variation in observed clinical signs existed between horses diagnosed by owners and veterinarians, with the latter group representing a more severely af- fected cohort, as previously reported.10 Owners have proven reliable at using the clinical signs of vertical headshaking, rubbing the nose on the tho- racic limb, and snorting for the diagnosis of idio- pathic headshaking.10 As vertical headshaking was observed in over 90% of horses in this study, it is likely that owner-diagnosed horses were true id- iopathic headshakers; however, other causes of headshaking cannot be excluded. Likewise, details of the veterinary diagnostic procedure of the veteri- narian-diagnosed horses are also unknown. In field situations, veterinarian diagnosis of headshak- ing, like owner assessment, is usually based on ob- servation and history. A single veterinary exam has limitations, and there is no diagnostic test for headshaking. Idiopathic headshaking is a constel- lation of signs, which persist in the absence of a rider, independent of tack, and apparent lack of underlying pathology (i.e., sinus mass, iris cyst, etc.).4,11,12 The authors, therefore, feel that veteri- nary diagnosis and owner assessment of clinical signs, which are the basis of any headshaking diag- nosis, are both equally valid. Nose nets were the most frequently used treat-


ment for headshaking having been used by almost 90% of respondents. Whereas some degree of im- provement was seen in over 50% (58/110) of horses, complete resolution of headshaking was rare and observed in only 5%. These improvements are lower than that previously reported where use of nose nets resulted in some decrease in clinical signs in 75% of 36 headshakers in the UK13 but greater than the 33% improvement reported in the U.S.7 Geographical location was not analyzed in this study due to the heterogeneous nature of the data. In this study, nose nets resulted in one of the highest rates of positive outcome and, therefore, represent a simple first-line therapeutic option. Such physical treatments avoid competition medication regula- tions; indeed, the use of nose nets is now permitted in some equestrian disciplines. Adverse effects of nose nets have not been previously reported, to the authors’ knowledge, but were observed in approxi- mately 1


⁄3 of horses and were reported for both types


of nose net. Owners should, therefore, be advised of the possibility of irritation or panic upon their application. The method by which nose nets reduce clinical signs of headshaking is unknown; however, it is postulated that they reduce aversive stimula- tion of hyperesthetic areas or, alternatively, the con- stant presence of the net might work by adjacent receptor field inhibition or receptor adaptation of the contact area.14 Interestingly, some owners re- ported a waning of clinical effect with time raising the possibility of habituation. A positive treatment outcome of 53% (44/83) of headshaking horses with a face mask was similar to


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