Horses in New Zealand should be grazed away from areas where they might ingest the seeds of sycamore maple and box elder trees, a veterinary journal report advises.
Horses that ingest the seeds are at risk of developing the serious muscle disease atypical myopathy. Clinical signs may include muscle weakness or stiffness, colic-like symptoms, laboured breathing, dark red-brown urine, recumbency or even sudden death.
The disease has been linked to the ingestion of seeds from the sycamore maple (Acer pseudoplatanus) and box elder (A. negundo) only in recent years. Evidence has been mounting that the disease is caused by the toxin hypoglycin A – an amino acid derivative – found in the seeds.
Dr Rabecca McKenzie and her colleagues, in a clinical communication in the New Zealand Veterinary Journal, reported that during April and May 2014, four horses in the Canterbury, Marlborough and Southland regions presented with a range of clinical signs including recumbency, stiffness, lethargy, dehydration, depression, and myoglobinuria (the presence of myoglobin in the urine) suggestive of acute muscle damage.
Two horses were euthanised while two recovered. Seeds of sycamore maple or box elder trees were present where the horse had been grazing in all cases, the researchers reported.
Hypoglycin A was detected in the serum of affected horses but not in healthy controls used in the study.
To determine if hypoglycin A was present in the seeds of Acer trees in New Zealand, 15 samples were collected from box elder and sycamore maple trees throughout the country that were associated with cases and analysed for the toxin. Hypoglycin A was detected in 10 of the samples.
The researchers reported that sycamore and box elder trees in New Zealand are a source of hypoglycin A associated with the development of atypical myopathy.
“If pastured horses present with clinical and biochemical signs of severe muscle damage then the environment should be checked for the presence of these trees,” they said.
Horses should be prevented from grazing seeds from the trees, which are prevalent in autumn.
Detection of hypoglycin A in the seeds of sycamore (Acer pseudoplatanus) and box elder (A. negundo) in New Zealand; the toxin associated with cases of equine atypical myopathy
R.K. McKenzie, F.I. Hill, J.A. Habyarimanac, F. Boemerd and D.M. Votione.
NZ Vet J. 2015 Nov 22:1-17.
The abstract can be read here.